How Important Is Soil Temperature?


| 3/26/2015 9:28:00 AM


Tags: seed starting, soil temperature, Cindy Conner, Virginia, blossom end rot,

 compost thermometer in coldframe

This time of year gardeners are anxious to plant their seeds. I know because even in the dead of winter I would run into gardeners who told me they could hardly wait. But, wait you must, until the soil is warm enough. Otherwise, it is like sending your children into the cold without their jackets. They might not die (the seeds or the children) but the cold shock will set their health back. Actually, in the case of peas, beans, or corn, if the soil is too wet and cold the seeds could die, which is why you might see those seeds coated with fungicide in garden supply stores. You do not want or need fungicide treated seeds. When you plant under the right conditions, the seeds will sprout readily and grow healthy plants. You can find more information about soil temperature for specific seeds at Homeplace Earth.

The date of the last expected frost in your area is often a guide as to when to plant — either at that time or so many weeks before or after that date. A couple weeks before that date you will probably experience an upward spike in air temperature. It will get warmer, even hot, tempting many gardeners to put seeds and transplants for their warm weather crops into the ground early. However, more cold will be on the way before the weather settles, so be careful. Also, it takes longer for the soil to warm up than it does for the air to warm.

The year 2012 messed with everyone’s garden. There didn’t seem to be any real winter and very little spring before summer was upon us. If you had a planting schedule worked out you had to take another look to see if that was really what you wanted to do. My small grains, wheat and rye, were ready to cut early, both for mulch and for grain. I needed to go by the signs the plants were giving me, not the date on the calendar. Nature gives us such signs all the time. The study of recurring plant and animal life cycles and their relationship to weather is called phenology. Some gardeners keep their own records from year to year about when things bloom and other observations.

Even when you’ve thought you have taken everything into account, the weather could still throw a wrench into your plans. I remember one year when gardeners were complaining about their tomatoes having blossom end rot and mine did, too. We knew we had waited to plant until after our “safe date” and that our soils had enough calcium and not too much or too little water. It turned out that we had a short spell of colder than normal weather after the tomatoes were in. It wasn’t cold enough to kill them, but it did set them back. After that first flush, the rest of the tomatoes were fine.

So, you never know. Do the best you can and be ready to roll with whatever nature throws at you. Save your main plantings for when all the signs are good, however, if you are adventurous and have seeds and plants to spare, you could plant outside what is considered their normal comfort zone. If you just really want to plant early, put up a high or low tunnel to warm the soil. Remember, there are no mistakes to be made, only learning experiences.




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