Minimum Soil Temps for Various Crops and Weeds

by Keith Brown, Divide County North Dakota Extension Agent

The minimum soil temperatures for germination of various crops are as follows: 40° for spring wheat, durum, barley, canola, mustard, safflower, field peas and lentils; 45° for oats, chickpeas, and sunflowers; 48° degrees for flax, and 50° degrees for corn, soybeans and dry beans. The optimum soil temperatures for rapid germination and emergence are about 5 to 10 degrees warmer than the minimum temperature for a specific crop.

While it is most desirable to wait until the soil warms to near optimal temperatures to seed, we seldom have that luxury. Most of the crops that we seed in this area are cool-season crops, which on average yield better when seeded early. Plus, as farms have gotten larger, we really need to take advantage of any available planting windows to get everything seeded on a timely basis. This generally means that we need to start seeding when soil temperatures are closer to the minimum than the optimum for germination.

When seeding into soils at or near the minimum germination temperature for the crop, consider the use of basic seed treatment products. Seed planted into cooler soil will take longer to germinate and emerge, which means that it will have greater exposure to soil pathogens. Seed treatment will help provide protection against these pathogens, which can reduce stands due to seed rots and seedling blights. It will also help protect the seed or seedling if we run into adverse conditions following seeding which further delays emergence, such as cool, wet spell or a late spring snow storm.

Weeds that are considered cool-season that emerge with minimum soil temperatures of 35-40° include winter annuals such as prickly lettuce, shepherdspurse, frenchweed and annual weeds such as kochia, wild mustard, wild buckwheat, russian thistle, common lambsquarters, and wild oats,. Early emerging perennial weeds are Canada thistle, quackgrass, and absinth wormwood. Weeds are considered warm-season that emerge with minimum soil temperatures above 45° or higher include wild sunflower, cocklebur, marshelder, ragweeds, biennial wormwood, redroot pigweed, foxtail species, nightshade species and lanceleaf sage.