How bit are the pots? I had 4ft Dahlias in wide 5 gallon pots and they weren't big enough. Its not so much getting root bound as you need to water very frequently to keep the soil moist. Now have them in 12 gallon pots and that seems maybe a bit bigger than necessary, but they're no longer wilting at mid-day.

hmmmm. maybe they aren't getting enough water but they never wilt. i do give them quite a lot of water. perhaps the pots are too small. maybe i'll try transplanting the ones in smaller pots and see if that helps.

Its quite a bit hotter and drier here than it is where you are, plus my containers are on patio that probably reflects some heat, so your symptoms may well be different.

For what my 2 cents is worth, here it is.

I have about 25 dahlias in the ground and about 25 in pots. My experience (and most dahlia and rose vets will say the same) is that potted plants NEVER seem to do as well as in- ground plants do. But they can do fine anyway and bloom just fine.

My question would be are you feeding them? And if so, with what?

I made the monumental mistake of withholding Miracle Gro from them last year (even bought 0-20-20 fertilizer) and I had some that looked just as yours are described. They sprouted like weeds and grew to 2-3 feet and then went into hibernation. A couple never bloomed at all. This year, I gave them 4-5 doses of MG so far and some have started blooming already, all are up and growing and it looks like the exact opposite of last year. One of my potted plants last year gave me about 4-5 blooms all year but already it has 2 blooming, 6 waiting to bloom and hopefully many more to come.

Good drainage in pots is key. When the soil never dries out, my dahlias get saggy looking and sometimes die. Then again, potted plants dry out quicker that soil plants so as mentioned above, they may need MORE water.

Many will tell you pot size makes a difference and I don't doubt it does, but I wonder why store bought, already blooming dahlias are doing fine crammed into 1 gallon plastic pots? I suspect they are not grown in pots but I also can't see a 4 ft dahlia with three 8" blooms being transplanted from the ground into tiny pots either. Surely that can't be good for them so which is it? They were transplanted or grown from scratch in 1 gal pots?

The bottom line is they do well in those small pots so maybe smaller is better? (Somehow, I just can't wrap my head around that idea.) Maybe some of the vets on this board can straighten me out about that.

David

My very amateur understanding is that what really matters is that the plant is getting enough water and nutrients. If water and nutrients are abundant, the plant needs less feeder roots than if they're scarce, although there's obviously a physical limit imposed by the maximum capacity of the root system, so you can't grow 4ft tall dahlias in 4 inch pots because the roots physically wouldn't be able to carry enough water to keep the plant fed. Hydroponically grown plants have relatively small root systems for their size because they have a constant supply of water and nutrients in a small space, but they're also very fragile - cut off the water for even a day and they'll be severely stressed. A plant grown in the ground, especially if its not irrigated or fertilized, will have a much larger root system and consequently can take much more abuse.

Container culture is in between. Provided they get a constant supply of water and minerals sufficient for their size, there's no fundamental reason container plants can't do as well as those in the ground, but its hard to keep the supply constant. Its easier with a bigger, well-drained pot than with a smaller one because the mix can hold onto more water without becoming waterlogged and killing the plant's roots. If you're going to grow Dahlias in containers, its also important to note that they need some nitrogen and there almost certainly isn't enough a in store bought mix. From what I've been told, its probably best to give them about 2x as much nitrogren as phosphorus, but I've not tested this with any care.

I've been wondering what's up with the Home Depot dahlias myself. My guess would be that they're grown under carefully controlled lighting with lots of nutrition to get them to grow and bloom quickly, and then repotted into the little 1 gallon pots you see them in in the store. I wouldn't want to leave them in those pots in the conditions I can give them for very long.