What is the optimum rooting medium tempture for most plants?

Question

What is the optimum rooting medium tempture for most plants?

Answer 1

This is very dependent on the plant. Germination and root growth is very closely tied to soil temperature and how it fluctuates between night and day. For each plant there will a maximum and a minimum range but in general in temperate, spring germinating plants the upper limits will be 30 C while the lower limit is 10 C in the soil.

Tomatoes are tropical so will not grow if the soil cools below 12 C.  Tomatoes produce roots  above 14 C but double root growth above 20 C. Tomatoes are damaged if the soil goes to 30 C.

Corn does best at 25 C with up to five times more root growth than seen at 18 C. Carrots grow best about 18 C and if the temperature drops below 10 C they may lose color, shape or flavor making their best range 15 - 21 C.

Other plants adapted to an early start simply pause when the occasional late snow flurry cools the soil back down. Trees like pine, spruce, or alder that are adapted to cold climates will produce excellent root growth above 9 C but drop off in growth rate until it stops at about 5 C.