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Field, garden soil temperatures for germination

By Staff | May 15, 2020

The arrival of spring has many farmers and home gardeners itching to get planting, however let’s take a moment to visit about the minimum soil temperatures required for germination of various crops or groups of crops. Soil temperature is a factor which few of us consider important enough to check before planting but yet it is one of the most important factors affecting seed germination, stand establishment and seedling growth. For example the minimum soil temperature required for germination of many cool season crops is 40 degrees this includes spring wheat, durum, barley, canola, mustard, safflower, field peas and lentils; 45 degrees for oats, chickpeas, and sunflowers; 48 degrees for flax, and 50 degrees for corn, soybeans and dry beans. Keep in mind that these are the minimum temperatures needed for germination – Optimal soil temperatures for germination and emergence are about 5 to 10 degrees warmer than the minimum soil temps.

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. If the soil is wet, this will also favor the activity of many soil-borne 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 a cool, wet spell or a late spring snow storm.

Most seed treatment products are registered for on-farm use, either for drill box application or to be applied in a mist or slurry with an auger treater. For information on current seed treatment products registered on all crops in North Dakota, check the 2020 North Dakota Field Crop Fungicide Guide (Extension Circular PP-622) available at www.ag.ndsu.edu/publications/crops/north-dakota-field-crop-plant-disease-management-guide. Always read the label carefully and follow the label directions for application procedures, rates, and specific diseases controlled.

Since I also mentioned home gardeners, let’s shift gears and take a moment to discuss the minimum soil temperatures required for germination of various garden vegetable crops or groups of crops since soil temperature is probably the most important factor affecting seed germination and plant growth.

For hardy vegetables such as broccoli, cabbage, kohlrabi, onions, lettuce, peas, radish, spinach, and turnips, the minimum soil temperatures required for germination is 40 degrees, however, onions, radish and spinach can tolerate germination temps as low as 35 degrees. All of these hardy vegetables can often tolerate some late spring frost.

Semi-hardy vegetables such as beets, carrots, cauliflower, parsley, parsnips, potatoes, and chard can also germinate at soil temps of 40 degrees but are less tolerant of late spring frosts.

Tender vegetables such as beans, celery, cucumbers, and summer squash can germinate at minimum soil temperatures of 60 degrees, however, corn can tolerate germination temps as low as 50 degrees, but should all be protected from late spring frosts.

Very tender vegetables such as cantaloupe, eggplant, pepper, pumpkin, winter squash, tomato, and melons can germinate at minimum soil temperatures of 60 degrees, but are intolerant of both frost and cool spring winds so it is best to wait to plant these sensitive plants until daytime temperatures are consistently above 60 degrees.

As with our agronomic crops, optimal soil temperatures for germination and emergence of our vegetable crops are about 5 to 10 degrees warmer than the minimum soil temps.

Information on soil temperatures can be obtained from the North Dakota Agricultural Weather Network (NDAWN) station. Additional information on soil temperatures such as the average daily soil temperatures and soil temperatures under turf can be obtained at the NDAWN website which is ndawn.ndsu.nodak.edu. Near real-time weather data can be viewed from any Web-browsing device, including smartphones.

Soil temperatures at the Rugby station as of Monday, May 11th were 43 degrees F for bare ground and 391 degrees F under turf.

– Submitted by Pierce County NDSU Extension Agent Yolanda Schmidt

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