Here's a little trick I tried and found helpful. Use a shopvac and vacuum out the soil from around the tuber. This will keep the sprouts intact and preserve any roots that may have started.

As far as watering goes, while my tubers have been sprouting I kept the soil fairly dry (e.g. dry down to the first knuckle on my index finger) and damp below that. Assuming the tubers are plump, they have all the moisture they need to get your sprouts started at this point. You merely want to keep the outside of the tuber slightly damp. Mist at least daily, possibly more if your house is dry, to keep the foilage from drying out.

You're not really going for roots at this point because too much root growth now would make it harder to transplant, and limit the foilage growth.

Try and make sure they get 14 hours or more of light a day, that will help prevent tubers from growing (i.e. new tubers on the new roots.)

Good luck!

Cheers,
Russ

Thanks Russ. So I should just leave them in the pots they're in, and suck out the soil around them? The tubers are quite plump and seem healthy enough. I have a misting bottle out there, so I'll mist them once or twice a day. It swings between 30 and 45% humidity out in the greenhouse, depending on outside temps.

It gets light around 6:30am at the moment, and dark around 7:30pm, so they're getting around 13 hours of daylight at the moment. That will get longer daily, of course, but it's about the best I can do right now.

Thanks again for the tips - I appreciate it! Hubby loves dahlias, so we wanted to at least try a few this year. :-)

No, Jamie, I was suggesting to take them out of the pots they're in using a vacuum to make the move easier for the tubers (because we don't know what they've done since you put them in the pots and the vacuum let's you uncover them without really disturbing them. Of course if your vacuum is really strong, you could simply suck them up which would be bad...;-])

Bottom line, put them in their own containers as you've read. If you leave them where they are until you're ready to plant out (e.g. May 24) the roots may be tangled. Not the end of the world, but now you can do what you thought (put them in their own milk carton) which would be better.

I would love to be where your greenhouse is, in Z4 or Z5, and getting 13hrs a day of sunlight. I'm Z5 and can't get more than 6 hrs of direct light. I could be wrong, but perhaps you need to think about light in terms of actual sunlight on your plants and not just when the sun comes up and goes down. Perhaps your greenhouse makes that question moot, but perhaps not???

BIG QUESTION!: Why is it you're doing this for hubby if you don't love Dahlias, or, why isn't he here asking? I'm a guy, its not like we can't love flowers!!...;-] And, its not like we have to make you love them too...why don't you like them? (beyond the obvious...he makes me do all these posts to figure out how to make them grow...;-])

Cheers,
Russ

In zone 4/5 I would be more worried about lingering low temps than watering or vacuuming. I can't imagine a vacuum involved in dahlia tending at all, except to clean up the floor where I've been potting! I think that would do more harm to any small roots than good, IMHO, but I can see your rationale for preserving roots Russ. In less than a week's time of being potted, I don't think you'll have any trouble pulling them out of current pots and repotting or re-milk jugging, Jamie.

I've had great luck growing dahlias in 12-14 inch pots, just over a foot deep. Smaller than that might work too.

Watering: barely damp soil works best in the early days. They don't need much until roots are formed to absorb that water. I don't routinely mist, but we've got nothing but damp out here this time of year.

Watch your temperatures in the greenhouse, don't let em freeze, water sparingly until they are up and growing several inches and re-pot at will and I bet you'll be enjoying dahlias in a couple months' time.

Poochella, thank you - that helps a lot. I'll repot them into milk cartons as I'd planned, and water them sparingly. They're all coming up and the leaves look really good, so I can't have screwed things up too badly yet. :-)

I have a heater in the greenhouse - it never falls below 50 (normally it stays around 58-60 at night and on cold days, but if it drops into the teens at night, it gets down around 50 or so). So freezing isn't an issue at all. I have veggies and annuals growing out there right now that I started from seed - a freeze in the greenhouse would be a complete disaster for our gardens this year.

Russ, I did say 13 hours of "daylight", not "sunlight". My greenhouse is situated where the sun hits it very early in the morning, and is on it all day, no trees or anything shading it at all (doors and vents stay open all day on warm, sunny days to keep the heat managable between 70 and 85 or so, and there are fans running in there 24/7). There are about three microclimate zones in my yard - the greenhouse is in the warmest, full sun microclimate, where I have roses (my favorite flowers) starting to leaf out already. I have all manner of annuals and veggies growing out there in the greenhouse, and none are getting leggy at all, so I'd think that if there's enough light for tomatoes, there's probably enough light for the dahlias to get started. They're coming up fine, as I said, the leaves look good, so I think they're getting plenty for now. Obviously as the days get longer, they'll have light longer. I'm not on the "mountain side" of the state - south-central Montana (where I live) is closer to a desert than the cooler mountain regions in the western parts of the state.

And I never said I didn't like dahlias...I said my husband loves them (which he does). I like the flowers, but I have more of a passion for roses personally (don't have to dig them up in the fall). Maybe I'll fall in love with dahlias after growing them for a season or so - but I won't know if I don't try! My hubby doesn't care much for typing or forums, and he would never "make" me ask anything, anywhere "for him" (he wouldn't have asked for himself either...he'd just throw them in a pot and let them grow or not, as his dad does). I asked of my own free will, because I was interested in how to get them the best start possible. It's my nature to jump into whatever I decide to do with both feet. I am interested because I love my husband, he loves dahlias, and that makes me want to have some in the garden for him, regardless of some extra work in spring and fall. Have you never grown something just because someone in your family really likes it?

In any case, thanks for the advice. I'm sure we can get the dahlias off to a good start this year now.

Here I am in mud zone 7 and all you Canadians and Montanans are lightyears ahead on dahlia growth. Congratulations!

Your set up sounds very good Jamie, and I hope you'll be won over by the versatile, variable, and vivacious dahlia in 2008. There are so many to choose from: each with their own merits. I gave my roses away- too disease prone for this locale. I did like their scent and delicate petals, but dahlias are also most amazing in their fantastic petal formation, wide array of colors and color combinations and various forms and sizes. You can't beat 'em!
I can hardly wait to see my new ones and the old favorites!