This cultivation guide has been compiled by assembling information from experienced growers, industry professionals, and horticultural specialists. It has been tailored to the specific challenges of growing dahlias on Cape Cod with its unique maritime bordering on humid subtropical climate and poor soil conditions. The dahlia season here starts early in May and lasts well into Oct. The guide has been prepared by Ivan Bogdanov.
The key to growing dahlias well is full sun, rich well draining soil, and plenty of water and fertilizer.
Here on Cape Cod our soil is very poor (and often times acidic) and poses the biggest challenge. Augment your soil with plenty of rich organic matter and treat with lime if needed. You can also correct the soil problem by growing in raised beds which allows for the concentration of good loam and helps control soil temperature and drainage.
Place sturdy hardwood stakes where you want your dahlias to be, spacing them at least 2 feet apart for full size dahlias, and about 1 foot for smaller/border varieties. Mix a slow release fertilizer such as Osmocote Plus 15-9-12 (3-4mo) at a rate of 0.2lb per full size dahlia (half for smaller varieties) into the planting hole. Plant your dahlias 4-6” deep. Lay the tuber flat with the eye (or growth point) about an inch or so from the stake. Avoid watering until the dahlias sprout above the ground.
Bait for slugs as soon as the young shoots come up and throughout the season. To control insect pests and disease use a systemic insecticide and a dedicated fungicide (recommended Tristar/Eagle).
Top (stop/pinch) your dahlias at about 8-10” (~4 sets of leaves) for sturdier, bushier plants. For bigger blooms keep only the central bloom bud and remove the two side buds. Once the dahlias are in bloom, cut away, this will make the plant produce more laterals which results in more blooms. Side dress the plants with a low nitrogen fertilizer in Aug. Discontinue all fertilizer in Sep.
After a killing frost (usually late Oct/early Nov) cut the dahlias down to a few inches from the ground. Dig up the clumps in a week or so to allow for the plants to go dormant and divide the tubers making sure each gets a piece of the crown. If unsure where the eyes are, half or quarter the crowns. Label your tubers with the variety names and let them cure for a day or two by laying them on a flat surface or grate in a cool dry place away from sunlight. Store for the winter in coarse vermiculite or red cedar shavings and in a cool place ideally about 40-45 degrees. Cover but do not seal storage containers to allow air flow. Check periodically for rot and mold, and remove any affected tubers. Take out of storage in mid-April and plant in early to mid-May.
SUN: Full sun
SOIL: Rich well-draining soil (pH ~6.5)
FOOD: Heavy feeders. Need plenty of balanced fertilizer
WATER: Deep water every few days
SPECIAL CARE: Tender perennial. Lift up in fall and store for the winter. Replant in spring.
Plant in early-mid May once the soil has warmed up and all danger of frost has passed.
Site dahlias where they will receive full sun. 6-8 hours a day is ideal. Less sun will result in weaker plants and bloom. Dahlias will tend to stretch or become leggy if they don't receive enough light.
Augment the soil with a good garden soil product and/or compost and/or peat. Our soil in Ptown is very sandy, so anything to increase its nutrient content and moisture retaining will be extremely beneficial. In fact, if raised beds are an option, it's definitely the way to go. Liming the soil at the recommended rate to balance its pH is also often beneficial in our area.
Cultivate the soil. Tilling is preferred.
Staking is also recommended at this point for any dahlia that will reach over 3 ft (most dahlias will). Use sturdy stakes (6ft 1" hardwood stakes work great). Painting the stakes a dark green color will make them disappear in the foliage. Average spread for a mature dahlia plant is about 2 ft and average height about 4 ft. Keep that in mind when planning your dahlia beds.
Dahlias usually come in the form of tubers, cuttings, or nursery plants. Tubers need to be planted horizontally 4-6” deep and a couple of inches away from the stakes with the growth point (aka "eye") facing the stake and pointed up (don't worry too much if the eye doesn't face up, it will find its way). Cuttings and nursery plants are planted at soil level. Best to wait to plant those in late May.
DO NOT WATER newly planted tubers or they may rot. Wait for them to show above ground to start watering. The only exception to this rule is if spring has been unusually dry. In that case, a light watering is recommended but take care not to overdo it. There generally is enough moisture in the soil for early development. You can water cuttings and nursery plants normally. Cuttings will take a lot more water than nursery plants until fully established due to their limited root system.
Once dahlia sprouts show above ground you can begin watering. Water deeply and less frequently versus briefly and often. A good soaking once or twice a week should be plenty unless the weather turns hot and dry in which case you may need to water every other day or even daily. We generally have to water more than usual on Cape Cod because of the fast draining soil.
Setting up an irrigation system will be very beneficial since proper hand watering of half an hour per plant takes a really long time, if you have multiple plants. Focus on watering the root area more so than wetting the leaves.
Reduce water in the fall.
It is highly recommended that you mulch your dahlias as that will help keep the soil temperature even, maintain moisture, and control weeds. You can use several kinds of mulches but make sure that you do not use any mulch that contains weed killer (read the package, weed killer is usually listed at the bottom). Weed killer will destroy your dahlias. Straw mulch is generally considered best but you will have good results with pine, hemlock, cedar, or anything along the lines. Make sure to keep the mulch a couple of inches away from the dahlia stalk.
It's best to do a soil test (over the counter tests are available from nurseries) before deciding on what kind of fertilizer to use. A soil test will let you know what your soil pH is (ideal range for dahlias is 6.2-6.5.) and what nutrients are deficient in your soil. The soil pH not only determines the plant's "comfort zone" but also the availability of nutrients. If the pH is outside the ideal range, your fertilizer regimen will suffer because the plants cannot absorb the nutrients you're feeding them. Should your pH be lower than optimal, use a lime product at the recommended rate. PH is very unlikely to be too high in our area but use your acidifier of choice if that is the case. Here is a brief chemical break down of plant nutrition:
The primary macro-nutrients plants need are nitrogen (N), phosphorus (P), and potassium (K). Nitrogen is responsible for the green growth, phosphorous for flowering and rooting, and potassium for the overall health and vigor of the plant (including its pest/disease/drought resistance). Tissue analysis of plant matter shows that average macro nutrient ratio in actual plant matter is 20:3:14. Meaning that nitrogen is needed the most, followed by potassium, and phosphorus is needed the least. The secondary nutrients are calcium (Ca), magnesium (Mg), and sulfur (S). And the micro nutrients (which are only needed in trace amounts) are boron (Bo), manganese (Mn), copper (Cu), molybdenum (Mo), iron (Fe), zinc (Zn), chloride (Cl).
Fertilizers are listed in terms of their NPK content (example: 10-10-10) which tells you what % of the dry weight of the fertilizer each of the macro nutrients comprises in that order. Regardless of your soil test, you will need to add nitrogen to the soil since nitrogen depletes rapidly while phosphorus and potassium accumulate (in fact, P and K are often found in sufficient amounts in the soil around here). At the same time, you should be careful not to add too much nitrogen since it can result in lots of green growth but not many flowers and weak roots come fall. Each dahlia plants will need about 0.05lb of nitrogen per growing season. This translates into about 0.5lbs of 10-0-0 fertilizer, or 1lbs of 5-0-0. Because our soil on Cape Cod is sandy, acidic, and nutrient poor, supplying secondary (esp. Ca and Mg) and micro nutrients (esp. Fe) is also beneficial.
Conventional wisdom is to start dahlias off with a high nitrogen fertilizer to encourage green growth and then switch to a low nitrogen fertilizer later in the season to encourage flowering and better root formation. It is important to understand that lowering the nitrogen increases bloom not pumping up the plants with excessive phosphorus as manufacturers lead us to believe. This is because when nitrogen is reduced, it slows down green growth without slowing down photosynthesis, so the plant has a surplice of energy it can then put into flowering. A ratio of 1:2:2 is widely recommended in dahlia literature (especially: 5-10-10) but that seems to stem from incorrect application of nitrogen rather than actual plant needs. In fact, a ratio as high as 3:1:2 can be used to start, switching to a ratio of 1:2:2 or even 1:1:2 later in the season. Regardless of whether you use synthetic or organic fertilizer (your dahlias don't care, nutrients are nutrients), the total ratio of plant nutrients between what's available in your soil and fertilizer should be within these parameters. There are many products that can be effectively used to fertilize dahlias but generally no single product is appropriate for the entirety of the season and sticking to a twofold approach is ideal. Below are some different regimens that would produce similar results:
Pretreating the planting beds with bone meal is another thing you'll often find in dahlia publications. Bone meal supplies a little N, lots of P and Ca and they are bio available to the plants over a very long period of time. That's because organic fertilizers require microorganisms to break down the nutrients to a form the plants can utilize and that's a gradual process. There is very little risk of fertilizer burn when using bone meal (as is typically the case with most organic fertilizers). Note that fertilizers generally do not contain Ca, bone meal based ones are some of the few do. Ca can also be supplied if you apply lime to raise the pH of the soil (which again might be needed with the fairly acidic state of the local soils). Please be mindful, that if you do pre-treat with bone meal, you need to fertilize throughout the season with low phosphorous to balance the nutrients. That means supplying mostly nitrogen. Sources of high nitrogen based fertilizers are many: blood meal, fish meal, feather meal, bat guano, chicken manure, calcium nitrate, ammonium sulfate, urea, etc. Again, keep the nitrogen within the 0.05lb per plant per season limit and give it to the plants gradually. You might also need to supply micronutrients because none of the above contain these. Also be advised that a lot of critters will dig where bone meal is used. Sprinkling crushed red pepper on the ground will prevent that. After a couple of weeks it should no longer be needed.
Another (simpler but pricey) way to fertilize your dahlias is through resin coated slow release fertilizers such as Osmocote or Nutricote. They can be pre-mixed or applied during planting. You need only about 0.25lb per dahlia per season and it releases slowly over several months which greatly reduces the risk of fertilizer burn. Incorporate these in the top 3-4 inches of soil (above your planted tubers). This is a very safe way to fertilize your dahlias, however, it is more expensive than other synthetic methods. Please keep in mind, that the nutrient release is soil temperature based (warmer temperatures means more rapid nutrient release while the opposite is true when it's cooler). Recommended formulas are Osmocote Plus (15-9-12 + micros) or Nutricote Total (18-6-8 + micros). Generally you only use these once per season at planting (look for uncovered release in the range of 3-5 mo), but adding an extra scoop per plant around the beginning of August can be beneficial because it staggers the time release. You could also augment with a different low nitrogen product at that point.
If you decide to use commercial synthetic formulas (10-5-10, 10-5-5 etc) you need to understand that they are highly concentrated and release quickly, which means you have to incorporate these gradually over the course of the season. Top dress by using a small amount, broadcast it over a large area, and lightly scratch it in the soil. Do this every 4 weeks by dividing the recommended amount of nitrogen over the entire growing season. It is very easy to burn your dahlias with fast release synthetic fertilizers, and once stunted the plants take a very long time to recover (if they recover at all). These fertilizers, however, are the cheapest option when you have a larger number of plants. Unless cost is a limiting factor, this type of fertilization is best left to commercial/field growers and not recommended for the average home grower. Choose one of the other suggested methods instead.
MiracleGro liquid feed (24-8-16) can also be used to effectively fertilize dahlias. MiracleGro is designed to be used bi-weekly. You can also apply MiracleGro Bloom Booster (10-52-10) once the plants start budding but it has such an excess of phosphorous (too much phosphorus can lock up iron and other micronutrients) that it should not be used continually, and instead should be applied only once or twice.
A great organic supplemental product to try is Dr Earth Flower Girl (formerly known as Organic 8 Bud and Bloom Booster) with NPK of 3-9-4. This product comes packed with probiotics- a mix of beneficial bacteria and fungi that boost the plant's overall health (see below RE mycorrhizae). It can be used like bone meal above in a pre-treatment regimen, or as a finishing fertilizer to any of the above regimens (after Osmocote/Nutricote, after a synthetic, or after Miracle Gro). One can also make fertilizer tea with it and apply by watering or spraying the plants. Instructions for that can be found on the package and there is a video on the Dr Earth website.
Lastly, dahlias are endo mycorrhizal. What this means is that like many plants on earth their roots form a symbiotic relationship with beneficial fungi in the soil. These fungi attach themselves to the dahlia roots and greatly increase the ability of the roots to absorb water and nutrients. They also supply the plant disease fighting chemicals. In exchange the dahlias provide sugars to the fungi. Poor soils and regular cultivation decrease the amount of mycorrhizae in the soil so adding those can be beneficial. Because dahlias are a tuberous root crop, this supplementation has an even larger effect than it does on plants with fibrous roots. Even though this is not a fertilizer per se, it is a fertilizer enhancer. Out of the products above Dr Earth is the only one that has endo mycorrhizae, but these can be supplied by purchasing inoculum, or through some soil amendments (Coast of Maine Bumper Crop is an excellent choice).
Whichever fertilizer you decide to use, err on the side of caution and follow the product labels. Keep the total nitrogen within the recommended limits and provide sufficient amounts of the rest, and the dahlias will award you with excellent growth, health, and blooms.
Discontinue all fertilizer use in late summer (Sep). This is particularly important with nitrogen as late season application of high nitrogen will weaken roots.
It turns out we are not the only creatures that absolutely love dahlias. Open centered dahlias are magnets for bees and other pollinators. Sap spiders often find shelter in the cupped florets of doubles. And even tree frogs are known to nestle in the florets of the larger blooming varieties. Unfortunately, a lot of insect pests also find dahlias irresistible. In our area we mostly have to deal with: slugs, leafhoppers, spider mites, aphids, earwigs, and flower eating beetles.
The biggest trend in the horticultural industry right now when it comes to handling pests and diseases is the so called Integrated Pest Management (IPM). Without getting into too much detail the basic notion is that instead of spraying and forgetting and over-treating with chemicals you don't need to use, you focus on monitoring for signs of pests/disease, suppressing by encouraging natural predators and keeping your garden tidy, and worse comes to worst sparingly treating with target chemicals to knock out infestations. So let’s discuss ways to handle pests/diseases, hopefully without hurting the beneficials. Keep in mind, the best time to spray treatments is late afternoon, early evening. This minimizes impact to pollinators and also helps with preventing the breakdown of chemical treatments due to UV exposure. Investing in a decent sprayer is a good idea, it will save you a lot of time with treatment application.
Slugs are the vanguard of the pest army! They will eat dahlia shoots before they eat anything else. If left unchecked they will quickly destroy the young plants. The good news is that it's fairly easy to control slugs but you have to stay on top of it. Many home remedies, like leaving beer out, or cutting strips of aluminum cans and encircling the stalks work great. When a more thorough control method is needed, you can use any of the readily available slug bate products with iron phosphate (recommended brand: Monteray Sluggo, OMRI listed). Most work really well and tend to be more effective if applied after wetting the soil (which encourages slugs to become active). Slug bate needs to be reapplied often throughout the season and especially during the wetter spring and fall. Avoid bates containing metaldehyde since they are toxic to children and pets.
Leafhoppers usually come next. These guys look like little green bugs with blue and red stripes that turn dark brown when mature. They feed on the sap of the plants and cause the leaves to look stunted, twisted,and deformed. If leafhoppers are allowed to reach infestation levels they can cause crop failure. To make matters worse, not only do they cause damage to the plants but they are also vectors for disease, in particular virus spread, which can cause long term stock decline even if the actual leafhoppers do not kill the plant! Imidacloprid is the chemical that is most widely available and used to control leafhoppers (many brands, ex: Merit, Bayer 3in1). Imidacloprid is a systemic neonicotinoid insecticide that enters the sap of the plants and kills all insects that feed on it. It also happens to be highly toxic to bees both on impact and through its residual effect and is blamed for the colony collapse syndrome that has been plaguing the bee populations all over the world. Imidacloprid is, in fact, now banned in Europe. We suggest that if you decide to use a systemic you opt for Tristar SL (acetamiprid) which is a bit harder to find but is only toxic to bees if you spray it directly on them and up to 3 hours after application. That can be easily avoided by spraying later in the day as recommended above. Tristar is long lasting, effective versus multiple pests, and resulting in fewer applications.
There are also some organic products you can use to combat leafhoppers- insecticidal soaps and pyrethrin (recommended brand: Pyganic). Keep in mind, these are also harmful to bees upon contact but like Tristar have no long term residual effect on them. Soaps can burn open blooms so be careful when applying those once bloom commences. Chromobacterium subtsugae (recommended brand: Grandevo PTO) also works well and is nontoxic to bees (although it does have a repellent effect on them for a few days). Organic solutions are non-systemic and need to be applied more often. Another great way to naturally keep leafhoppers under control is by employing their natural predators such as green lacewings, lady bugs, and pirate bugs. Green lacewings tend to be the most effective since they are voracious, and generally stick around the area they were released. You can get these online from various sources and they come as eggs, larvae, or adults. The former is best for early season pro-active control, the larvae is best for infestation control, and adults are used for better species establishment. If you’re using green lacewings as part of an IPM program with Tristar, please understand the product has moderate toxicity to them for up to 3 weeks after application so you would need to time their release with that in mind.
Aphids along with leafhoppers are probably the worst insect vectors for spreading virus disease in dahlias. You can see aphids on the underside of leaves and growing points. There are two most common kinds, the green aphids, and the dark colored ones. The former being easier to handle than the latter due to different habits. You may also see ants farming the aphids for sap. Ants will in fact bring aphids to an area and clip their wings so they cannot escape and then proceed to farm them for sap. Insecticidal soaps and predatory insects (especially green lacewings known in their larval stage as "aphid lions") are excellent in killing aphids. Should you have a more serious infestation on your hands, Tristar SL will do the job.
Mites (esp. Spider Mites) are next on the list. They are usually not a problem early in the season but when the weather turns hot and dry they can be devastating. That's why some people wet the undersides of the leaves to prevent mites from establishing. Although somewhat effective, this invites mildew problems later in the season, so we do not recommend it. Mites can cause total crop failure, especially since they are very prone to reaching infestation levels (3-5 day life cycle between egg and laying eggs). They are usually very hard to see with the naked eye but their damage is easy to recognize. You will see mottling/puckering of the effected foliage and webbing on the underside of the leaf (where the mites reside).Mites are notorious for developing resistance to chemical treatments so oftentimes these need to be rotated and applications are generally capped to 2 times per crop per season. The following work well, however, are very expensive-Sultan (spider mites ONLY), Shuttle (spider mites mostly), and Avid (ALL mites). Members can obtain smaller doses of these chemicals by participating in bulk buys during the spring. An organic approach to mite control that is sure to work and not result in resistance is predatory mites. These guys can be voracious eaters. There are several species available on the market. Some offer broader control than others, and also some are better at prevention and for establishing, while others are better at infestation control. Phytoseulis persimills is particularly good in controlling spider mites. You can use Sultan and/or Shuttle as part of an IPM program with predatory mites since these only kill spider mites not all mites. That will extend your coverage due to the 2 times per season treatment cap. Avid is not recommended for IPM due to residual toxicity to all mites. Also please be mindful that Avid resistance is wide spread at this point. It can, however, be alternated with Sultan or Shuttle in a rotation program, since these will kill the Avid resistant mites.
Earwigs are omnivores that can on occasion be beneficial by controlling certain pests but are most often a pest that causes irregular chew marks on the leaves and often hide in the flowers where they also chew up the petals. They will sting you if provoked. Earwigs like cold damp places, and leaf litter. So good garden practices go a long way in controlling these. You can also use traps made out of cans filled with vegetable oil, tubes of rolled newspaper, or bates with Spinosad (recommended brand: Sluggo Plus). Tristar SL works on earwigs as well, Pyganic is also effective.
Flower eating beetles
Flower eating beetles may become a problem when flowering commences in late July. They are particularly fond of white dahlias and will chew up the petals. You can manually remove them and drown them in a bucket of water but that requires daily maintenance. Tristal SL works well. So does azadirachtin- a neem oil organic derivative (recommended brand: Azatin-O $$$, can use a cheaper brand such as Azamax but the chemical concentration is lower). Azadirachtin is a broad spectrum growth regulator that is also effective against aphids, leafhoppers, etc. It does need to be applied weekly for best results but it is OMRI listed.
Wireworms and other soil dwelling pests
Wireworms are the soil dwelling larval stage of click beetles. They can bore into and damage tubers. They rarely cause the plants to fail but can impact their overall health and the quality of the roots come fall. You can bate wireworms by cutting a potato in half, spearing it with a stick and placing it underground with the stick serving as a handle. Remove in a couple of days and discard the wireworms that have accumulated. Another organic method is the use of beneficial nematodes which are microscopic roundworms that naturally occur in soil. These worms enter their hosts and release symbiotic bacteria that proceed to kill the host within one to two days. They are very easy to apply- you can spray them with a tank sprayer like you would any other chemical or mix them with water and peat (or vermiculite) and apply as a top dressing. Beneficial nematodes will also will kill most other beetle larvae, cutworms, leaf miners, etc. It is best to use Steinernema carpocapsae (recommended brand: Millennium) but you can also use a combination of species for broader effect. Apply before planting and follow the instructions for your chosen method of application. Always apply at dusk since sun will destroy them. Keep the soil moist during application because they travel better in moist soil (that is why this is better done prior to planting). You only need to apply in spring and fall. Stagger applications for better population establishment. Tristar sprayed at the base of the plants is also effective. Spinosad (recommended brand Conserve) works well, too.
Now let’s discuss powdery mildew and other fungal diseases. Since we live near the ocean, the humidity in our area is very high and this is a common problem for us. Powdery mildew is another one of those "will kill entire plant if left unchecked" problems. Prevention is the best approach. Space your plants well, allowing for plenty of air circulation. Remove the lower 2-3 sets of leaves once the plants mature to further improve air flow and also prevent insects such as mites from spreading. Do not wet the leaves of the plants excessively. The use of a dedicated fungicide is highly recommended. You could apply as soil drench in the beginning of the season since mildew actually resides in the soil and then migrates in the plants later in the season or you could use foliar spray. Mycobutanil (recommended brand: Eagle) and chlorathalonyl (recommended brand: Daconil) are two that are most frequently used in horticulture. Eagle is unique in the fact that it is a curative and protectant, while Daconil is a suppressor only. A newer product that is broad spectrum and works well in alternation with the above is Pageant. And for the organic growers there is CEASE and the newer Triathlon BA. Both are beneficial bacteria based and they work by colonizing the plant matter and preventing disease establishment. Triathlon is also a bactericide, meaning it is effective against some bacterial diseases.
Last but not least, dahlia viruses are some of the most tenacious diseases affecting dahlias. Viral diseases are actually quite common and most are not terribly detrimental or obvious. Affected plants can show no symptoms of being affected. Other times they may display some symptoms when young but quickly "outgrow" them. However, they can succumb to what looks like nutrient deficiencies but has been proven to truly be caused by viral infections. Some viruses cause chlorosis or yellow veining on the leaves. Others can cause ring-like yellow patterns on the leaves. Still others can cause puckering or bubbling of the leaves. And last but not least, there are viruses that cause necrosis or stunting and die off of the leaves/plants. When symptoms are obvious, the best course of action (and the hardest one to hear) is to cull the plant. Yes, it might grow OK, even bloom, however you're running the risk of insect vectors like leafhoppers and aphids which are quite common to spread the virus to healthy plants and eventually cause them to fail. The American Dahlia Society has invested a significant amount of money into virus prevention research and the results so far point at culling as the best practice to achieve a virus free garden. Most growers will see virused dahlias at some point in their growing years and keeping the garden virus-free is a tough but necessary task. I should mention that application of chelated iron is worth a shot, since if it is soil or growing conditions related stress, chelated iron can correct that, and the plants might not need to be culled. As a general rule ensuring the plants are grown in optimal conditions and rich soil will greatly improve their overall health and disease resistance and you will see fewer incidences of viral disease.
Keep in mind there is always a chemical vs organic approach and it's up to you to choose which works better for your situation. Good garden practices go a long way in reducing the need for chemical treatments. Keep your dahlia beds clean, well-trimmed and maintained, with ample spacing. Encourage beneficial insects (some plants like sweet alyssum make wonderful companions to dahlias due to their ability to attract beneficials). Cull diseased plants to prevent spread of disease.
(Special thanks to Rick Yates, GGSPro Tech Services Team Manager, for thoroughly reviewing, correcting, and updating the information in this section)
Once dahlias sprout above ground, keep only one sprout. This ensures best flower production and makes the bush much tidier. You should also top the dahlia off after 3 or 4 sets of leaves. Carefully remove the growth point in the middle by peeling the immature leaves back and pinching center. Try not to expose the hallow central chamber as that could invite rot. Topping will cause your dahlias produce four main laterals and make for a better spaced bush. Once the laterals begin growing and leafing, you can also remove the lower two-three sets of leaves. What this does is it allows for air flow (which helps with powdery mildew) and also makes it easier to spray the plant underneath with chemical treatments. This is very important when dealing with pests such as spider mites which infest the underside of the leaves. Also feel free to remove the leggy lower laterals that the plant may put out from the very bottom as these are generally leggy and break easy. When the dahlia starts budding, only keep the terminal or center bud, and discard the lateral two buds. This ensures the biggest blooms and again helps keep the bush tidy (otherwise the central blooms will tend to get lost in the foliage, which negatively impacts overall appearance). If you're growing blooms for exhibition, you should remove additional laterals to focus the strength into the terminal bud. In fact, giant and large dahlias are commonly grown to four blooms only while mediums are grown six to eight blooms for exhibition purposes.
The more you cut your dahlias, the more blooms they will produce. So cut away! You should also deadhead and cut off any disbudded stems down to the viable growth points. Cut in the early morning or early evening for best results. You can sear the ends by placing the newly cut blooms in hot (almost boiling) water. This helps set the bloom and makes it last longer. Leave the blooms in the hot water for about an hour making sure they are spaced well so the heat coming off the water can escape and not damage the floral heads. You can then cut to desired length and use in vases and arrangements.
You could also temper the stems by dropping them in ice cold water. Adding floral food to the water is also beneficial. Any readily available product would work (you can also just add a spoonful of sugar). From this point forward the cooler the area where the blooms are, the longer they will last. A florist moisture sealant product such as Crowning Glory will additionally extend the life of your flowers. Try to keep the blooms away from direct sunlight. Be mindful, dahlia blooms last at best around five days.
exhibition/cut flower industry only
Dahlias are sun loving plants, however you can greatly improve the quality of the bloom if you use netting/shade cloths/or umbrellas. This is done for exhibition purposes or for cut flower trade. Shaded blooms will tend to open up fully without any sun damage. Deep colors such as reds, purples, pinks, and lavenders will also be heightened.
You could use arbors and pull shade cloths/netting over during show times. You could also use regular or golf size umbrellas attached to the supporting stake. For light blends and light colors, use clear umbrellas as they will do the job without bleaching the light colors. Apply shading sparingly as its purpose is to enhance blooms at specific times (a week or so before a show, for example). The plants still need to get full sun for healthy growth.
After a killing frost, cut your dahlia bushes to a few inches above ground, and let the root set for ideally 7-10 days. This allows the plant to enter dormancy and will also encourage the eyes or growth points to become more prominent. You can cover the stalks with aluminum foil or plastic bags to prevent moisture from accumulating in the exposed central chamber which could lead to rot.
Before digging the clump, remove the support stakes, adjust any irrigation systems installed, and clear out any mulch or landscape fabric around the plant. Gently loosen up the soil around the stalk by hand- this will break down any compacted/crusted soil on top which could make digging harder. Make sure to dig at least a foot away from the stalk as dahlias like to spread. Make a full circle with the shovel, pushing straight down to cut off any excess roots. Use the shovel to lift the crown by carefully pushing up on it from the circle you dug. Once you can see the crown, use your hand to loosen up any soil in the spaces between the tubers as you lift. The longer you grow certain varieties the more familiar you will become with what their roots look like, how many tubers they produce, and how well these will store. Use this knowledge during digging to help you lift thicker rooted varieties faster, while allowing more time to gently dig around varieties that make thinner, longer tubers.
Rinse off the clumps well to reveal the crown and tubers. Some people rinse them in large buckets or wheelbarrows, others use a plastic or metal grate of some sort that allows the excess soil to pass through. Make sure to keep track of the varieties. You can do that by keeping the plant label with the clump at all times.
Use sterile tools to divide. You will need a pruner to make large cuts. For the finer work, Zenport Delux scissors work really well. Thin garden snips are also useful. Dip tools in bleach water between cutting different clumps- this ensures you will not spread disease, should one of them be a host without having shown symptoms. Clip off any excess roots from the main tubers, shorten tubers that are too big, and remove tubers thinner than a pencil (these will not store well). Discard the old mother tuber (you should be able to barely make out the labeling on it, and it will also tend to be much darker and more gnarly in texture than new growth). Make sure each tuber gets a piece of the crown. The crown is where the new growth will come from in the spring. If you can see the eyes on the crown, allow for at least one eye per tuber, otherwise the tubers will not grow. If you cannot see the eyes you can quarter the crown and keep a couple of tubers per piece.
To label your tubers you can use an indelible marker (pencil) or a Sharpie to write the variety names on them. Indelible markers work only when the tubers are slightly damn so it helps to have a spray bottle or damp paper towel around. Also be careful when sharpening these to keep the end a little blunt, otherwise it may tear the skin of the tuber. Sharpies only work when the tubers are dry, so you might need to wait for that before labeling. It's usually easier to read labels made with indelible markers.
Let the tubers cure for a couple of days before storing. This is an important steps since tubers that are too damp when stored are more prone to rotting. Monitor them for signs of shrinkage. They should remain firm and healthy looking. Their surface should be dry. If they start shrinking or getting soft, you should discard them as they will not store well.
Gently shake the tubers in a plastic bag with sulfur dust (you can also add coarse vermiculite as a tumble medium) or dip in a fungicide solution (recommended Cleary 3336F, which is systemic). If you shake in sulfur dust, you will need your tubers to be dry, if you use a fungicide dip, you can do that while they are still wet. Although this step is not necessary, it will kill any fungus spores and serve as a mold preventative. Anything that increases your storage survivability odds can only be beneficial.
Store the tubers in coarse vermiculite or red cedar shavings for best results. You can purchase coarse vermiculite from lumber yards for less than horticultural vermiculite. (Coarse vermiculite is used for insulation). Red cedar shavings should be available at pet stores. We recommend red cedar due to high phenol content (phenols are disinfectants so they aid during storage). Store in plastic tubs. Cover but do not seal. You can store individual varieties within the tub in Ziplock veggie bags (these are vented). You can also use regular plastic bags but make sure to poke holes in them. Ideal storage temperature is 40-45 degrees, so a utility room, or dry basement, or garage works fine for the most part. Check the tubers periodically and discard any shriveled, molded, or rotten tubers immediately as this may spread.
Bring the tubers to a warmer place in mid-late April. They should have visible eyes at this point or start eyeing shortly. Plant in early to