Cool Season Vegetables

For vegetable gardeners, it is time to think about cool season vegetables.  Focus on garden planning, seed buying, and soil preparation, such as incorporating compost, if the soil is not too wet.

Do not let air temperatures trick you into planting too early. It is soil temperature that needs to determine when planting begins. Gardeners who plant too early may end up harvesting later than those who wait. And some can end up reseeding or replanting.

Ward Upham, Extension Educator with K-State, says one of the most neglected tools for vegetable gardeners is a soil thermometer. And he is correct. If vegetables are direct seeded or transplanted into cold soil, seed can rot and transplants can just sit there and not grow.

Even if seed does not rot, seedling emergence can take 10 days or much longer in cold soil. If seed germinates, seedlings may die from damping off which are diseases infecting slow growing seedlings.

When this happens, gardeners are not any further ahead than if they had waited until soils warmed. If seedlings and transplants make it, growth may be stunted which can delay harvest and reduce yields.

For cool season vegetables like lettuce, radish and peas, it is recommended to wait to seed until soil temperatures are above 40 degrees Fahrenheit, with 45 to 50 being ideal.  For warm season vegetables, like beans and sweet corn, it is recommended to wait until soil temperatures are above 55 degrees.

To know when to plant, consider buying an important garden tool. Metal soil thermometers are inexpensive and available from garden, hardware and auto parts stores.

Upham provides these tips for taking soil temperatures accurately. Take the temperature 2.5 inches deep at about 10 to 11 AM. Temperature variations throughout the day and night affect soil temperature, with lowest readings after dawn and warmest around mid-afternoon.

The late-morning reading gives a good average temperature. If taking the soil temperature at this time is not practical, take a reading before you leave for work and a second when you return home and use the average. Get a consistent reading for four to five days in a row before planting, and make sure a cold snap is not predicted.

Soil temperatures for Nebraska are also available on the UNL Crop Watch website at

If you do not like to wait for nature, and still wish or need to plant earlier, here are a few things to try. Soils in raised beds warm faster so consider raised bed gardening. Some gardeners place black plastic over the row to speed soil warming. Others pre-sprout seed before planting to get a head start.

Once soil temperatures are warm enough, pre-sprouting can speed emergence. To pre-sprout, seed is placed on a moistened paper towel. Fold or roll the towel and place it into a plastic bag with some holes in it, then set it on top of the refrigerator for warmth. After 5 to 7 days, check the seed. When the white root, begins to develop, carefully plant the seed outdoors.

Another method for early season gardening is with the use of hot caps. To learn more, Nebraska Extension has a NebGuide titled “Early Season Extension using Hotcaps” available at

By: Kelly Feehan, Extension Educator

Release: March 9, 2017