When do they need sunlight? What are good temperatures?

megbun(5b MA)April 10, 2013

Hi everyone,

I'm brand new to dahlias and am in the process of giving them a head start, since I'm a New Englander. I managed to do some nice dividing from my random garden center tubers (I think I'll get 13 plants from the 5 tubers I purchased). I followed the instructions on this forum, so I got my tubers to eye up in little plastic baggies, including a number of tubers I thought had no eyes. Great tip!

Few questions:
1. I have one odd chunk that has its sprouting eye in the middle of a cluster of 3, but it's on the underside bured in between. In other words, the sprout is going the same direction as the tubers are sprouting roots. Any ideas for how to handle that? Should I try to remove one of the tubers, so I can at least place it on its side?
2. I've potted up the tubers with eyes that are sprouting in small clay pots of varying sizes, lined with newspaper for easy transplanting. I only barely covered the tubers with soil. I'll fill up as they grow. When exactly do they start needing direct light? When the sprouts break the surface? Or is it only when the sprouts start having leaves?
I ask mainly because I have limited access to light inside. At what temperature can I put them outside in their pots, at least during the day? At what temperature should I be concerned about losing the tubers, even on our screened-porch? I can keep them inside all the time where it is going to be 65-70 all the time, but I'm concerned about lack of light. Ideally, I'd like to keep them on our porch when it's chillier (and at night) and put them out in the sun during the day.


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Sounds like you've done your homework, and are in the problem solving stage all dahlia growers have to work through.

As to your first question, most growers lay the tuber on its side, with the sprout facing up. The roots, as long as you cover them, will grow towards moisture. Without a picture, its hard to tell how I'd trim an oddly shaped tuber clump.

With your second question, I had flats of well-sprouted tubers outside in what I thought was 45-50 degree weather in order to add potting mix to the containers and water thoughouly,and had some cold damage on several plant leaves after I came out after dinner to bring them back inside. I was surprised, and a bit chagrined. Perhaps someone else can quote you exact temps...

You might consider a cold frame, or a vertical 'greenhouse' that is basically plastic over a plant stand. That might add a bit of protection when the temp dips more then you reckoned on.

    Bookmark   April 11, 2013 at 8:58PM
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And to answer the question in the headline - they need light when they break the surface - but not if you are going to continue burying them for a while.

Lack of light will make for a long, weak spindly stem.

    Bookmark   April 12, 2013 at 7:56AM
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megbun(5b MA)

Gotcha (RE: sunlight). I also got a bit of an answer this morning from one of my tubers. One of my sprouts sticking out of the dirt actually has a couple of tiny little leaves on it! Very exciting. I assumed I was just going to kill all my tubers (not that I'm out of the woods yet).

So my question now: before developing leaves, do the sprouts need sunlight? Is leaf growth triggered by light hitting the sprout? Or is it temp? Level of root development? Something else?

    Bookmark   April 12, 2013 at 11:48AM
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