I would think the depth of the tuber is the primary reason. If they are to deep the soil won't be warm enough up where you live and to have mulch on top of the soil keeps the warmth of the sun on top of the ground. I would dig the root balls up and move the tuber to about 3"-4" inches below the surface, remove the mulch until they are growing well and give them some nitrogen to get them growing. Dahlias like the soil to be at least 70 degrees in order to make roots. You can mound dirt around the stem that has been below the ground until it hardens off to the sun. Another issue with the tubers so deep is drainage when it rains or when you water as they don't like wet feet and that will retard their growth or make them rot.

There's actually a pretty cool 70 seedling starter tray that Aerogrow makes for the purpose of starting your seedlings indoors.

(that first post was from my dad Larry) Don't wait to add the mycorrhizae, it takes a long time for it to become established in non-oxygen-infused grows. Add it in when you first mix up your grow medium so that its well entrenched before you get it outside. If you wait to add it until the transplant its benefits will not come into effect until 4-6 weeks later. It will protect your plant from in-ground pests and pathogens as well as ease the transplant process by advancing into the new soil along with the roots. I would encourage aggressive supercropping to keep the plant at a manageable size and to get it as stout as possible. If you do this the fan won't help much and would also prematurely pollinate any flowers that slip by you. I'm not sure potting up would help much since a good mycorrhizae colony will rapidly take over the surrounding soil once you get it outside, but I can't see it hurting anything either. You are correct about heavy nitrogen to delay fruiting and to encourage heavy vine growth. Its tricky to get this kind of fert without using a nitrogen-only fertilizer, which you DON'T want to do. The plant needs some, albeit relatively small amounts, phosphorus potassium sulfur magnesium and so fourth which you usually only get from a general purpose fertilizer which contains more potassium and phosphates than you would like. The solution is to use an organic fertilizer that I swear by called Fish Emulsion. It is a 5-1-1, the perfect ratio for vegging out a tomato plant. It also contains just about every trace mineral under the sun and then some. I would recommend fertilizing with it and fast-acting lime for a calcium boost so that your plants can load up on it preemptively. Fast-acting lime does raise the PH of your soil so you may want to counter-act it with some garden sulfur as well. Calcium is very important for forming the cell walls of the tomato fruit and a deficiency in it is the cause of blossom end rot. Better to prevent this than have to treat it down the road and if you succeed in getting a massive flush of fruit from an over-sized transplant then you will have abnormally high calcium and potassium uptakes. I'm going back and fourth on what I think of your flower-pinching idea. On one hand it will indeed prevent the plant from producing fruit which it won't be prepared to do with its low potassium and phosphate levels. On the other I see having flowers on the plant on the day of the transplant as a way of getting a head-start on your yields. Personally, I think since you are in an indoor setting lacking the insects and steady breeze (if you ditch your fan) that normally pollinate the flowers you should leave as many of them on as possible. I would only pinch off flowering locations that inadvertently became pollinated and started to swell at the base indicating the early formation of a tomato. Leave the rest. When you take the plant outside the flowers should rapidly pollinate from wind, insects and all of the jostling about that will surely occur when you transplant. Other than that I think your theory is very solid and should get you sun-belt yields in a short-summer climate. Good luck and happy gardening! -Zach

No I buy them from Steele Plant Co. I like to know what variety I'm planting and choose one that is said to be most adaptable to my area. There are other companies that sell them, I usually Google for a source. But I think it's ok to use one from the store. This year, there must have been some roots left in the garden beds, because I have about 3 or 4 plants growing, so not ordering new for this year.