12 frost-free weeks? In that case, plant them now into your greenhouse (I assume you can ventilate it during hot periods). You'll still get some crop, although with significantly undersized roots, whereas the chances of overwintering a tropical vine like that in a zone 7 greenhouse are minimal at best. Prolonged soil temperatures below 55 F will gradually kill the plants. It's not like overwintering a cool-season crop, which is adapted to going dormant and tolerating dark days and cold soils.

This post was edited by Slimy_Okra on Fri, Aug 16, 13 at 16:04

Thanks, slimy!

I hadn't thought of putting them in the greenhouse NOW, but I bet you're right; they would love it. Humid and a bit hot :). And yes, I vent it.

Ok, I know what you mean about overwintering some tropicals -- I have tried with squashes and nasturtiums, and they died, but not from frost. As you say, they just couldn't handle the length of time in the cool and dim.

I overwintered sweet potatoes in containers outdoors in FL, but that was zone 9, very rare frosts. They would die back some, but never completely and perk up again as soon as it warmed up a bit.

Since you are in zone 7, I would think you could keep them alive in a greenhouse, even if the vines die back. You are only trying to stretch a couple of climate zones. I'd avoid overwatering if it's chilly in there.

In Japan, maybe zone 7ish, I've seen people just leave a tuber on a sunny windowsill in the house during winter - no soil, just the root on a plate with vines growing willy nilly. I suppose they watered it occasionally.

Sweet potato slips can also be kept alive almost indefinitely in just a container of water. I've done it for months on end in a gallon jug.

If it were me, I'd try multiple methods to see what worked best. I'd try to get a few decent sized tubers and store them in a cool dry place. I'd leave a few in containers in the green house, and I'd take some cuttings to grow in a gallon jug in a sunny spot in the house.

Sweet potatoes need sun to size up the tubers, but otherwise fairly shade tolerant. The vines will probably not die from lack of sun - cold is the primary enemy.

If everything fails, I'll send you slips in springtime.

I am still planting new slips for my fall crop. One's going in now probably won't fully size up, but since the vines are EVERYWHERE and need to be cut back, I might as well propagate.

In florida, SP easily overwinters in the ground - that is, after all why the plant grows a tuber.

I agree with slimy that the chances of overwintering in a z7 greenhouse are poor. I have tried it without success here in 7a several times. Like Nila I have also had poor results in trying to grow slips in the spring - too cold.

One would need a properly designed and dedicated set-up, which would require as well expending energy on heat.

To accelerate rooting in the spring in a cold house, I place the SPs (in their jars of water) on a large heat mat and drape a piece of row cover, folded multiple times, over the arrangement. I can usually keep it around 85 F underneath, which seems to be the optimum temp. for encouraging rooting and budding.

>If it were me, I'd try multiple methods to see what worked best.

That's a good idea :).

>To accelerate rooting in the spring in a cold house, I place the SPs (in their jars of water) on a large heat mat and drape a piece of row cover, folded multiple times, over the arrangement. I can usually keep it around 85 F underneath, which seems to be the optimum temp. for encouraging rooting and budding.

I did that, with no success. I didn't stick a thermometer under the fabric though -- I will try that this year. I had the tubers cut and laying on soil surface, and didn't want to bake them, but I will try in water this year.

They finally sprouted outdoors in mid-july, but have stayed the same size since then. The uncut ones on the kitchen counter are bigger!

>If everything fails, I'll send you slips in springtime.

Oh, my, thank you!