I've never used anything BUT Miracle Gro potting soil (or another equivalent brand) and had no issues at all. I feed with Miracle Gro as well, plus Milorganite and soybean meal.

Contrary to popular belief, dahlia are moderate feeders and really do like their nitrogen. Just not too much at once.

Moving them shouldn't be an issue in late May as the weather here in PA is completely dahlia-compatible by then, although the move alone is likely to shock them a little bit. They should recover--just keep them well-watered, limit the feeding, and give them full sun until they look good again.

I actually like the miracle grow moisture control for small pots. I do find that it is a bit too heavy to start seeds. I do like to cut it with one part peat moss a done part perlite and one part coco coir just to lighten it all up for tuberous begonias.

I've managed starting seeds in MG potting soil, but it does take a dab hand at balancing the water amounts. It's much easier if you cut the soil.

Dinner plate dahlias, bedding dahlias, it's all good. MG's soil's only real down side is the expense. You may be able to get a store brand that does just as well.

You can start the dahlia up here at your daughter's place if you want, but keep in mind that the weather here is still what I'd call "friggin' cold." Keep in mind I'm east-central PA near the Jersey border, so if your daughter is down near Philly it's merely "cold."

We're due for wintry precipitation again this weekend, with no real end to winter in sight just yet. They'll have to tolerate a sunny window until around May fifteenth anyway, and that will probably stunt them worse than moving them.

I don't plant my tubers until at least May first (sometimes slightly earlier if the weather indicates no frost, but that's unusual). They're usually in bloom by the end of June. Their depth is enough to protect them from a late frost and they won't sprout until mid-May anyway.

Seeded dahlia (Figaro, Harlequin, and Fireworks) get started and go under light banks in March for planting out in mid-May. Blooming on those is early June.

Thanx again morpheuspa,,,,so what I am hearing is that you think it would be better to start dahlias south ...my plan was to leave in sunny window..(we also live east central jersey border pa !! Maybe we're neighbors ..) in an effort to get earlier blooms this yr..typically they dont bloom til mid/late August..

Hmmm...what to do.....decisions,,,,decisions...

Six on one, half dozen on the other. An earlier start might help them bloom earlier...if they're getting enough sunlight to develop. That's about four hours of direct sun per day absolute minimum (six would be far better).

Really, a well-planted dahlia should blossom about six to eight weeks post-planting, and I've gotten that down to four by feeding well and making sure they have a LOT of sunlight (eight to ten hours). It does depend somewhat on the dahlia as well. Most of my cultivars seem to be fast.

I too winter in Florida and summer in Michigan. I always start about a dozen tubers in peat pots while I am in Florida carry them home in a large plastic tub and plant in Michigan. It has worked good for me