Ideal Soil Temperature Range

by Chris W
(Kemptville)

Hi Scott,

A while ago mentioned a potential project for using surplus solar thermal energy to assist with vegetable growing.

I was wondering if you could advise me on the matter. Do you know what temperature range would be considered ideal for the soil to promote vegetable growth?

---

ANSWER
Great question, Chris. re optimal soil temperatures, it depends a bit on what you are growing,and if you are starting seeds directly in the soil or transplanting only.

In general optimum germination temperatures are higher than optimum growth temperatures. Example, beans (bush) optimum germination 23C-29C, optimum growth 17C-20C. Lettuce will germinate much lower <10C but will not thrive if root temperatures are much above about 18C. Many other greens e.g arugula, spinach, chard have similar characteristics.

There is also a relationship between available light and soil temperature, for example extreme ends of the season when light levels are low, lower temperatures will produce slower-growing but sturdier plants.

As a compromise I would suggest a range of between 18C-20C would work for most stuff; seeds would germinate and root growth/nutrient uptake would be adequate. If you have the ability to have different beds at different temperatures you could optimize for 'hot' and 'cold' plants.

Scott