Breaking tuber dormancy

SteveM · 2025-04-18T01:51:09+00:00

Even with ideal temperature and moisture, the ability of a tuber to break dormancy depends (at least in part) upon the conversion of starch into sugar duri...

Mel_McVay

I started some of my tubers in pots to break dormancy. I saw that @Teddahlia had posted somewhere that the trial gardens would grow plants in a gallon pot for a month before planting in the ground, to make sure they would better withstand any heat waves. This sounded like a good idea to me. I also thought it would be fun to start the tubers in clear pots so I could watch the root development. But now I’m realizing that when I go to harden these pots off outside, sunlight will be hitting the roots through the clear pots. And as roots are typically underground and not receiving direct sunlight, this was probably a huge mistake. Thoughts?

SteveM

Mel_McVay Thoughts?

I didn't know they made clear nursery pots. Your instincts are correct in that you don't want the sun to shine on those mini-greenhouses because the temp will get too high, both in the soil and around the leaves. You should be fine if you shade the pots, maybe by setting them inside a larger opaque pot, or inside a box, or inside a paper bag, etc...

If you don't mind, a question: Why do you have the pots filled with only a few inches of soil?

Teddahlia

Mistake. Also no drainage holes at bottom of container is a mistake. They both drain water and aerate the soil so rot does not occur. As you may know I consider all these "break dormancy" posts to be a pile of crap. It is an "either or " situation . (1) you want some growth from the tuber to get a head start on the growing season. Long sprouts on tubers cause the tubers to grow slower, not faster. (2) Breaking dormancy means only that the eye has swelled a tiny amount and anything longer than an inch slows up the tuber when planted. (3) If you want to get earlier blooms , grow a tuber in a gallon pot of potting soil and it will have hair roots and GREEN leaves and it is a plant not a pile of skinny sprouts. And really it is a hell of lot of work to place tubers into gallon pots with expensive potting soil and moving them around so they see some sun. Yes , we do that at the trial garden but we have 10 -15 volunteers working there.

Mel_McVay

Teddahlia Thanks Ted, lesson learned. For what it’s worth, that is a gallon pot and it does have 16 drainage holes. (I just took it out of the watering tray for the picture.)

Mel_McVay

SteveM Thanks Steve, those are good ideas. I’m sure I can find a slightly larger opaque pot and set the clear one inside.

This is my first year starting tubers, and I guess I was just feeling anxious and wanted to see it sprout and know that it was viable sooner rather than later.

Going forward I will cover my tubers with 4” of potting mix right when I plant them.

And I’ll go ahead and fill this pot up the rest of the way today.

Thanks for your patience and guidance.

SteveM

Mel_McVay Going forward I will cover my tubers with 4” of potting mix right when I plant them.

And I’ll go ahead and fill this pot up the rest of the way today.

I wasn't suggesting the tubers should be 4" under the potting mix. I was just curious why you didn't have the tuber in a full pot of soil. I think the depth of soil you have above the tuber is perfect. I was curious because I do the same thing for unicorn tubers. I use a heat mat (I grow outdoors in the Winter) so I place the tuber in a shallow mix (in one-gal pots) so that the temperature at tuber level will be 70F-75F. If I start them in a full pot of soil they are too cold and will not eye out until much later. I think your clear pots are interesting and may be a good canary to monitor the soil moisture (if all pots are watered equally) and to monitor overall root health.

calico20hill

I start most of my tubers in 4" pots. just enough to get some roots growing and some top growth showing before the ground is warm enough to plant them out. I do not let the pots get filled with roots...the vigorous grower get moved up to bigger pots. With a raised bed I can plant out earlier because it ALWAYS has good drainage. Once it is past the spring frosts, I think they do better in the bed and get them established hopefully before the summer heat arrives. Also, it is not hard to dig a hole deep enough or big enough for the contents of a 4" pot. I get the top of the plant where I want it and the roots can then continue growing as deep as they want. Our temperatures in the Pacific Northwest are usually moderate. We do get exceptions.

Mel_McVay

calico20hill That’s a good point about a 4” hole being easy to dig. I didn’t think about the gallon pots in the context of having to dig all those holes by myself 😂

I’m sure there’s a range, but roughly how long do you think you’re growing in the 4” pots before the plants go into the beds? Or maybe the better question is, how much top growth do you like to see before you move them to your raised beds?

MissyWeitzel

Lots of great advice here already. My 2 cents is: keep it simple for yourself. Dahlias are a lot of work at the end of the season if you have to dig, divide and store them. Let the beginning of the season be easier. Hardening things off is a pain in the butt, and can easily go awry. The fewer things you need to move in and out daily, the better. When you do harden those off and are at the point where plants are going from shade to getting a little direct sun, set timers on your phone so you don't accidentally fry things. Been there, done that!

Mel_McVay

MissyWeitzel Thanks Missy, that is good advice.

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