RAY FLORET: Dahlias are complex flowers. This means that in reality they are made up of bunches of tiny flowers. Each dahlia "petal" is actually a tiny flower. So instead of petals, which scientifically speaking are modified leaves, we say ray florets.
INVOLUTE/REVOLUTE: In dahlia form definition the words involute and revolute often pop up. Involute ray florets are ray florets that fold inwards, revolute ray florets are ones that fold backwards.
TUBER/EYE: Dahlias are tuberous plants much like potatos. Tubers are thickened roots that have stored nutrients in them. Each dahlia root produces multiple tubers over the growing season. These can be just a few or upwards of 20. Each tuber will produce a new plant next year provided that is has an eye. Eyes are growth points from which new dahlia plants emerge. They are usually by the stem or crown of the dahlia root, and quite often the tuber will form what looks like a head part around the eye. That is why when dividing dahlias we save a piece of the old stem/crown with each tuber.
DOUBLE/DISC CENTER: A disc-centered or open-centered dahlia is one that looks like a daisy with one or a few rows of rey florets and an exposed center. Any other kind of dahlia is a double (with a full floral head and a closed center, except for when the bloom is very old and starts falling apart, or "blows" its center as dahlia folk say).
The American Dahlia Society has developed a system to classify dahlias on the basis of size, form, and color. It makes it easier to group similar dahlias together.
SIZED DAHLIAS (DOUBLES)
SIZE: Not all dahlias are sized but the majority of doubles are. The first letters in dahlia classification are the ones for size. There are 5 size categories for double dahlias:
AA (GIANT) Flowers 10-12 inches wide
A (LARGE) Flowers 8-10 inches
B (MEDIUM) Flowers 6-8 inches
BB (SMALL) Flowers 4-6 inches
M (MINIATURE) Flowers under 4 inches
FORM: Form is the second set of letters used after size in dahlia classification. The shape of the ray florets determines the form of the dahlia. There are 6 forms that the above size categories apply to and between the two that will cover the majority of dahlias.
FD (FORMAL DECORATIVE) - These have an orderly appearance. Ray florets are generally flat and broad at the base with round or slightly pointed tips, and recurve towards the stem in a regular arrangement. Ideal depth of bloom is 3/4 of width.
ID (INFORMAL DECORATIVE) - These often look wavy and irregular. Ray florets are twisted, curled, or wavy in an irregular arrangement. Ideal depth of bloom is 3/4 of the width.
SC (SEMI-CACTUS) - These look sort of formal but are also kind of spiky. Ray florets are broad at the base and revolute (fold backwards) for about half their length. They reflex towards the stem in a regular arrangement. Ideal depth of bloom 3/4 of the width.
C (STRAIGHT CACTUS) - These are very spiky. Ray florets are narrow at the base, straight, and they radiate uniformly in from the center. They will be revolute (fold backwards) for the majority of their length. Ideal depth is 3/4 of the width.
IC (INCURVED CACTUS) - These are spiky but curve and/or twirl inwards. Ray florets are narrow at the base, and they curve and sometimes twist towards the center of the bloom. Because of that they lack the depth of the previous forms. Ideal depth of bloom is 1/2 of the width.
LC (LACINIATED) - These are very frilly looking. Ray florets are split at the tip and they twist and twirl in all directions (dahlias with splits that do not twirl are not classified as laciniated). Ideal depth of bloom is 3/4 of the width.
So a BB SC is a small semi-cactus dahlia (so right around 5" and kind of formal but spiky too), a A ID is a large informal decorative dahlia (so right around 9" and wavy looking).
OTHER FORMS (DOUBLE)
(BA/MB/P) BALLs - These are very tight and ball shaped. Ray florets are involute (so they fold inwards) and blunt without a point. They reflex towards the stem and fill the entire flower. These are further classified as Balls (over 3.5"), Miniature Balls (2-3.5"), or Pompons (up to 2") depending on the size.
(ST) STELLAR - These have a comet-like look. Ray florets are narrow and involute (folding inwards) and recurve towards the stem. Ideal depth of bloom is 2/3 the width.
(WL) WATERLILY - These look like waterlilies. The side view of the bloom is saucer like. The center is dome shaped and gradually breaks away into four to seven rows of florets. Ray florets are broad and slightly cupped with a round tip. Idea depth of the bloom is not more than 1/2 the width.
(NX) NOVELTY DOUBLE - This is basically for anything that doesn't fall into the above forms and/or looks like a blend of one or more of the above forms.
OTHER FORMS (DISC-CENTERED): These all look like fancy daisies.
(PE) PEONY - These look like fuller daisies. Between 2 and 5 rows of ray florets surrounding a disc.
(AN) ANEMONE - A dome of tubular disc florets surrounded by one or two rows of ray florets.
(CO) COLLARETTE - These look like daisies with a colar! One row of ideally 8 ray florets arranged in a flat plane followed by petaloids (frills) at about one half the length of the ray florets surrounding the disc.
(O) ORCHID - These look NOTHING like orchids, they instead look like star shaped daisies. One row of ideally 8 ray florets arranged in a flat plane. Ray florets should be involute for about 2/3 their length. Size irrelevant.
(OT) ORCHETTE - Newest class recognized by the ADS that combines the characteristics of an orchid (star shaped blooms) with the collar of the collarette types.
(S/MS) SINGLE/MIGNON SINGLE - The closest to a daisy a dahlia gets. One row of ideally 8 ray florets in a flat plane. SINGLE over 2 inches, MINGNON SINGLE under 2 inches.
(NO) NOVELTY OPEN - Any disc-centered dahlia that does not fall into the above disc-centered forms. Size irrelevant.
The ADS recognizes 15 different colors for dahlias:
White (W), Yellow (Y), Orange (OR), Pink (PK), Dark Pink (DP), Red (RD), Dark Red (DR), Lavender (L), Purple/Black (PR/BK), Light Blend (LB), Bronze (BR), Flame Blend (FL), Dark Blend (DB), Variegated (V), Bicolor (BI)
Now to make it more complicated, the ADS has a new 4-digit system, in which each dahlia has a 4-digit number that sumsup all of that stuff above. 1st digit is for size (if the form takes size, if not it's assigned), 2nd for form, and third and fourth for color. I won't cover this here as it's really only necessary for exhibitors at the shows, and 4-digit numbers can be looked up in the latest version of the annual ADS Handbook (comes free with ADS memberships or you can order from ADS website).
It generally takes four years for growers to roll out a new introduction. They do that because the first year is just a test to see if the seed will produce anything worth investing in and if it makes tubers so they're only grown to one bloom. The following years they test if the dahlia is genetically stable, that is if it keeps its form and color relatively the same over a couple of generations. They'll finally send the dahlia to the trial gardens that the ADS has set up throughout the country and take it to the shows in the hopes that it will get good scores and will be worth selling to the public.
Not all new intros are good intros. In fact, a lot of them will probably not be around for long. This on top of the price tag makes purchasing new dahlias a gamble. The ADS garden trials and show bench evaltuations are a way to sort through the new intros and see what's actually worth buying or keeping an eye on. The ADS awards medals to the highest scoring new intros.
HART MEDAL: Is for highest scoring new intro in garden trials. One Hart medal is awarded for each: AA-A, B, BB, M, BA/MB/P, WL, and ST&NX.
DUDLEY MEDAL: Is for the highest scoring new intro in bench evaluation. One Dudley is awarded for each (same as above)
EVIE GULLIKSON MEDAL: Is awarden for disc-centered dahlias (all forms). One is awarded at garden trials and one is awarded at bench evaluation.
This means a new intro can win up to two medals. Regardless of awards it is usually best to wait a season or two before ordering new intros- they would have proven their "worth" at the shows and will be cheaper to purchase (first year intros, especially medal winners can be $25 a tuber)
One more medal is awarded annually by the ADS
JOHNSON MEDAL: Goes to the dahlia variety that has won the most combined higher awards in a given show season. This award can only be won once. The ones that get this medal are definitely worth buying as they have proven their worth as an exceptional addition to the dahlia world. The Johnson usually goes to varieties that have won over 200 blue or higher awards at the shows. That's a lot! So definitely worth picking up something that is so overwhelmingly accepted by dahlia lovers everywhere.
Here is a list of the past ten years of Johnson medal winners from the ADS records (I'll use the abbreviations explained above for size, form, and color):
2015 - AC Abby (B C FL)
2014 - Parkland Rave (BB IC L)
2013 - Verrone's Morning Star (OT W)
2012 - Lakeview Glow (BB IC YL)
2011 - Elvira (PE DP)
2010 - Midnight Star (O DR)
2009 - Camano Sitka (B IC LB)
2008 - Pam Howden (WL LB)
2007 - Mary's Jomanda (BA DP)
2006 - Camano Pet (ST LB)
2005 - Valley Porcupine (NX LB)
2004 - Embrace (BB SC BZ)
2003 - Kenora Jubilee (A SC W)
Swan Island Dahlia (All around)
Biggest grower in the US. Good all around. User friendly website. Show varieties are a bit dated and new intros are very expensive but otherwise a good place to start your dahlia shopping. Catalog opens up the earliest of all suppliers. Visa/MC/Paypal accepted.
K Connell Dahlias (All around)
Supplier of buffer stock for our spring sale. Excellent quality at low pricing and reasonable shipping/handling. Check out the bulk buys if purchasing for landscaping purposes. Accepts check or PayPal only.
Accent Dahlias (All around)
Wide selection and highest quality stock. Solid new introductions that do well at the shows and look good in the garden. Website a bit dated. Mail order or CC by phone. No online payment option.
Clearview Dahlias (Collector/Exhibition)
Smaller grower. Sells almost exclusively Snohomish county intros (which are great), with very few other varieties (but all proven winners). Good stock and customer service. Great for show. Mail or Paypal (including CC).
Lobaugh's Dahlias (Disc centered dahlias)
Mostly known for disc centered dahlias. They've won many awards for those. They also have some other dahlias although not a very extensive selection but all really resonably priced. Mail or Paypal (including CC).
Halls of Heddon (UK)
Ships to US in Nov only
Great and only source of UK introductions. Will ship only pot roots to the US. Cost for shipping will be £19.95 for up to 6 pot roots, and £27.95 for 7-15 (it isn't recommended to get more than 12 as then you will need an import permit and that adds to the cost, or alternatively you will need to split in two shipments to avoid it and that will add to the cost as well) plus a handling fee of £8.95. Credit card accepted.
Dahlia Addict allows you to search the availability/pricelists of dozens of dahlia suppliers throughout the US and Canada for dahlia varieties by name. It's a great tool to help you source your favorite varieties and comparison shop.