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dahlias not growing tall

Port Sanilac, MI

I potted up my dahlias early this year and planted them the middle of May in a looooong row. Some are "normal" and some are only two feet high. They are budding and in some cases producing a dinner plate flower on a two foot plant. Looks kinda silly.

I used the same amount and quality of garden soil to plant them in and the lighting is the same for all. Were some of them really small tubers that put up a good start and then ran out of food? I thought I had heard that the size of the tubers doesn't matter because they use the tubers only until they produce roots to nurish them. I am really puzzled and disappointed. Any suggestions?

(Arlene) Southold, NY(Zone 7a)

Mine are all in the ground except for five in pots. Of course, three of the potted ones (no ID) are tall, while the ones in the ground are shorter than they should be. I have no idea why it happens or if it's just too early to expect them to get to 4 or 5' high.

With lilies the size of the bulb really does matter but not with dahlias.

My only weak thought would be patience. Let's see how they are by September 1st.

Port Sanilac, MI

OK, patience. I'll try.

Calgary, AB(Zone 3a)

Kays I had abnormally cold temps in the spring. AACK I have blooms at 2 feet! How funky weird is that! It's like I have a dahlia bed of border dahlias. I will be patient as Pirl says... I will be patient... meanwhile they do look prettiful anyhoo me thinks. Tres short but prettiful ^_^

Thumbnail by dahlianut
(Pony) Lakewood, WA(Zone 8a)

We had a really cold, wet spring here, and I have some that are behaving normally, and others that are still teeny. In one spot, I have three of the same variety right next to each other- one is tall, the other two are totally short. I have no idea. LOL

Calgary, AB(Zone 3a)

Ahhh the mysterious ways of dahlias.

(Arlene) Southold, NY(Zone 7a)

Prettiful is right, D'nut. I love that color!

West Caldwell, NJ(Zone 6b)

This is what I call Short Segment Syndrome, or S3. Typically I think this is a root growing issue, meaning they are not up to par for some reason, and above condition reflects below. How big are the pots? I have unpotted them to move to the ground and often found the feeder roots wrapped around the wall of the pot, whereas they would be spread out in the ground. Some potting soils are too low in nutrients for hungry dahlias I think, what did you feed them? I hope the smallies are not my tubers. :(

(Arlene) Southold, NY(Zone 7a)

Penhill Dark Monarch is the Queen of the Wimpies for this year. The height is listed at 4' but it only meets (not passes) the bottom rail on a standard post and rail fence surrounding the vegetable garden. It was planted with compost (rototilled in) and each plant got a handful of Super Triple Phosphate.

Here's the face in profile since I was late in getting out to get the photos and then from a few feet back.

We have an automatic irrigation system but the lack of normal rainfall is the only thing I can guess could be to blame for the stunted height...so far. Time may improve the plant: it can hardly get much lower! If it does, I will have a beautiful ground cover.

Thumbnail by pirl
Port Sanilac, MI

Tod, I think you could be right. Some of the pots were very small and yes, some of the plants did have roots wrapped around the wall of the pot. It could very well be a feeding issue with some of them getting more nutrients than others for some reason (small pots=little soil?). This was my first year of potting up my dahlias and I guess I have a lot to learn. Overall, I was very happy with the results as I had flowers really early until I realized some are refusing to grow.

You don't have to worry about this year's tubers, Tod; I planted them right into the ground and they are doing fine. I can't pick on last years either because it is definitely hit and miss as to which flowers are short or tall.

I have a question about next year's potting. (besides the size of the pots and the quality of the potting soil) that I hope someone can answer. Do you pot them all up and hope they have sprouts or do you wait until you see the sprout coming before you pot? This year, I sorted them all and potted the "live" ones every couple of weeks; it was a lot of work that way. Then, as it got later, I ended up putting them all in pots; most of those came up. I'm thinking of doing them all at once (in larger pots) about 4-6 weeks before transfering them to the ground. Will that work? Thanks for any suggestions

West Caldwell, NJ(Zone 6b)

I am planning to pot mine up, not early, but to avoid any soil villains, like wire worms or cabbage maggots, or just plain wet soil. When they are big enough I will move them. I am debating between 10 and 12 inch pots - not sure if I need 12 inch, and its a lot more potting soil cost. If I could start 255 pots early inside under lights I would, but that's impractical for me.

An issue I read about is that liquid fertilizer can often travel out of the pot and not remain in there long enough, not sure if that's the case, but if so, maybe a slow release solid would be better.

I don't like to plant any tuber without a sprout that I stored, but I will do it from an official seller. I don't get too many like that though.

(Arlene) Southold, NY(Zone 7a)

Would you consider using a wetting agent?

West Caldwell, NJ(Zone 6b)

So far I have only used a wetting agent to mix with foliar feeds and insecticide, that is CocoWet, to get them to stick to the leaves. In this case is it to hold in the liquid fertilizer? Maybe if it were OMRI certified. But someone had recommended not to just pot them up in potting soil, but to add part soil or sand. I wonder what is the best potting medium for dahlias?

This is what Swan Island had to say about container growing:

"If you choose to grow dahlias in containers low growing or dwarf dahlias work best. Container size should be no smaller than 12 x 12 per tuber. Use 2 parts garden soil, 1 part potting soil that has not been treated in any way. Water sparingly, overwatering to keep soil damp will result in rotting tubers in the pots. After plants are 12 high, potted dahlias will require extra watering and fertilizing to promote proper blooming. "

I would figure this could do as well for temporary potting.


This message was edited Aug 5, 2010 1:46 PM

Port Sanilac, MI

Sorry, I don't understand your questiion, pirl. What is a wetting agent? dahh

(Arlene) Southold, NY(Zone 7a)

Wetting agents make water wetter. Adding a tiny drop of any liquid dishwashing product to a container of Miracle Gro fertilizer, will help saturate the soil more efficiently and the fertilizer tends to remain available to the plant and not just run out of the drainage holes.

Interesting question about "the best" soil for dahlias, Tod. I'll go hunting and if I find anything I'll post a link to it on this thread.

(Arlene) Southold, NY(Zone 7a)

From Ortho Books:

(Numbers 1 through 3 was the introduction and examining the soil)

Dahlias prefer soil that:
4 is located in partial shade to full sunlight,
5 - 6 contains a good amount of humus,
7 drains well while holding sufficient moisture to sustain vigorous plant growth,
8 is well aerated,
9 - 11 has a pH around 6.5,
12 is not contaminated,
13 - 14 has a balanced supply of nutrients -- nitrogen, phosphate, potassium, and micro elements,
15 - 16 is uniform in texture and mix throughout the root zone, and
17 - 18 has a regular source of fresh water.
19 Check list for preparing soil and beds for growing dahlias.

While the above has value it's likely not what Tod or I was hoping to find. I will keep hunting for a basic soil "recipe".

(Arlene) Southold, NY(Zone 7a)

More than I bargained for here but it comes from the American Dahlia Society and it's very useful information, which I will bookmark:


The answer to the question, Tod, was any good soil-less mix that remains loose - nothing with clay. The author adds reconstituted water crystals. I just started using them this past spring and, with all the heat that the entire nation has suffered through, it has been a blessing.

I've used Fafard soil-less mix with great success for many years but I'm sure there are many other mixes that will do the job.

Calgary, AB(Zone 3a)

I start my tubers in 100% peat moss with compost and bone meal mixed under the tuber in 1 and 2 gallon pots depending on the size of the tuber. Once they have broken soil I fertalize them.They live in those pots for 2 months and then they go in the ground with more bone meal and compost.

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