Cucurbits and cold feet

I live in a short season cold climate, and a local horticultural fella suggested that soil temperature affected (impeded) the growth of a lot of cucurbits early in the season, even if the last spring frost had passed. Is this unique to cucurbits, or is optimal root development dependent on certain temperature ranges for a number of species?

Hi Caleb, Soil temps must be above a certain temp for good growth after seeding or transplanting. 45F for cool season crops (lettuce etc.) and 55F to 60F for warm season crops like tomatoes & beans. I'm not sure where cucumbers fall, but waiting until the soil is 55F would probably be the most prudent and insure rapid growth.

We share the same challenges of dealing with low soil temperatures in a short growing season climate which can be compounded by the very long season of freezing temperatures. If the snow cover is poor, a deep layer of frozen ground can persist, well after thawing of the superficial soil. This provides a deep reservoir of soil cooling. The nitrogen cycles and mineralization are also greatly changed below 50 F and rate of uptake of other nutrients and nitrogen can fall rapidly. From our experience, as Robert notes, nightshades (tomatoes, tomatillas, peppers) are very sensitive. We have been experimenting with cucumber varieties but all are sensitive. There really aren’t too many things that do really well starting out in cold dirt except for some perennials like fuki and rhubarb that have almost magical ability to grow out of still frozen ground.

Patience is not my strongpoint, so raised beds, tunnels and a large number of very hot Berkley style compost piles to heat up the ground are used. I think I had 13 compost piles going at one time at the beginning of the season, which can rapidly raise soil temps. The lack of patience got me into some trouble when I had unfinished piles that created their own issues with nitrogen immobilization but that is a temporary problem! This makes me look pretty reasonable compared to a neighbor that was so frustrated he was dumping gasoline and lighting it to warm his garden. This might be viewed as problematic on several levels .

It has made me a more effective gardener, since I started to test soil temps at various levels with a compost thermometer and learned to probe with a thin rod for the ice level. The dynamics of soil insulation and temperature cycle raise some special consideration for using hugelkulture in a cold, long winter climate, but that is a topic for another time.

Thanks Christine! Great info. A lot of farmers around here use various plastics, black or transparent agricultural plastic to heat the ground. I'm not a fan of plastic, and if the annual part of the system grows dependent on plastics, then you're on sketchy ground.

I've never heard of using gas. That's wild. Maybe for smaller gardens we could collect old thick glass panels and lay them out (potentially this might lead to compaction issues). Have you played around with using buried stones that catch the sun above the soil surface and conduct the heat down into the soil? Rob Avis used something similar to create a microclimate in Calgary where tomatoes will ripen outside.

Caleb, I agree about not using plastic. I used it in Colorado, briefly, but concluded it was not a good choice. Appeared to damages the soil structure. We do use movable cold frames to heat up and protect some of the annual beds. Works great; just remove when the temps rise. An they return them in the fall. And, yes, we do use rocks to hold heat for many of the trees and shrubs in the forest garden. We actually are lucky to have a south facing bowel for much of our growing area that creates a micro climate.