The spring warm-up begins

Farm Forum

Do you like to watch the weather on TV? I think that most gardeners try to watch the weather whenever they can. Of course now we can get up-to-the-minute updates on our smart phones but I still want to catch the weather forecast every day if I can. The weather and especially the temperature are very influential in what happens in the garden and we have little control over it.

Last week we finally saw some nice warm, almost early summer-like temperatures. It is amazing to watch the transformations that occur with the warmer weather. The coats disappear to be replaced by t-shirts and shorts. What looked like barren soil for the last few months suddenly shows signs of life emerging from below. Temperature is what drives that transformation.

Air temperatures and soil temperatures are linked but as you would expect, soils warm up much more slowly than the air and show little variation over time while air temperatures can easily vary by 30 degrees or more in a single day. There are many factors that influence how quickly soils warm in the spring. Dry, sandier, more exposed soil will warm more quickly than wet, clayey and shaded soils. Mulches and turf grass shade the soil and keep it cooler longer into the spring. This can be beneficial in keeping some plants dormant a little later into the spring to avoid spring freeze damage to tender shoots. If you look around, you will probably see where tulips have been planted up close to a home, particularly on the south side of the home, the tulips are growing quite rapidly. While other sites, that are more shaded or mulched will see later tulip emergence and growth.

Soil temperature can play a more important role in the early spring growth of many different kinds of plants than air temperature. This is particularly true for seed germination of vegetables as well as weeds. Radish seed can germinate in soil as cold as 40° while watermelon seeds need soil temperatures close to 75°. Prostrate knotweed can germinate at a range of soil temperatures ranging from 35° all the way up to 85°. Crabgrass, a common lawn weed, will start germinating when soil temperatures reach about 62° in the top 1-2” of the soil, which usually coincides with the time when lilacs begin blooming.

Vegetable seedlings and transplants also need certain temperatures to germinate as well as grow and produce fruit later in the season. Spinach, peas, radishes, cauliflower and head lettuce can be grown with minimum soil temperatures of 40 to 45° but have an optimum soil temperature of 60 to 65°. But they also will not tolerate high air temperatures that can occur in mid-summer so they need to be planted early in the spring or in some cases, planted again in late summer for a fall crop. Broccoli, onions, cabbage, chard, leaf lettuce, potatoes, carrots, turnips, beets and kohlrabi are in the next group that can be planted and will tolerate warm summer temperatures. Warm season vegetables like beans, sweet corn, squash and pumpkins need at least 50° soil temperatures while cucumbers and muskmelons need at least 60° and tomatoes, eggplant, pepper and watermelons need 65-75° soil temperatures.

It is quite easy to measure the soil temperature in your garden and around your yard. You can purchase an actual soil thermometer or just go to your local grocery store or kitchen aisle and look for an instant read thermometer, which is ordinarily used to check if your steak is done to the right temperature. These inexpensive thermometers range in price from about $5 to $30 and are also available online. Generally you will want to stick the probe about 2” down into the soil to get a reading. Take readings at several locations to get a good average of what the soil temperature is for your garden. Just clean it up well before you put it back in the kitchen drawer or your steak might have a little bit of a gritty taste the next time you use it.

Gardeners can also check their state’s climate data to get some idea of what your soil temperature might be. There are a number of different websites that you can use to check. For SD try; for ND; and for MN check or The National Weather Service is another good place to look for this kind of data. The soil temperature at various depths is generally reported, often at 2, 4 or 8”. The 2” and 4” soil temperatures are probably the most important ones to watch since that will be the zone in which your seed is planted and the seedling’s roots will grow.

For more information on planting vegetables see

For more information on spring garden activities see

A Good Time for Repotting

Do you have an old houseplant that has just gotten too big for its pot? Does it seem like it always dries out? Does it tip over easily because it is too top-heavy? Has the pot cracked open because of too much root pressure inside? Are roots growing out of the top of the pot? If you answered yes to a few of those questions, it might be time to give your plant a larger pot. Now is a good time to do it too because you can take the plant outside or into the garage to avoid a mess on the floor.

Before you start the process, you will need to get a larger pot. Generally look for a pot that is a “size” larger than the current pot. So, if it is in a 6” pot now, look for an 8” pot. Generally you want about an extra inch of space around the root ball in the new pot for smaller plants and 2” or more space around the root ball for larger plants. I always recommend getting pots that have drainage holes. This allows excess water to drain out of the bottom of the pot when watering. You will probably need to use a pot saucer to catch the extra water but it will keep it from getting onto your window sill or floor. It is a good idea to empty the saucer after all the water has drained out, so that it is not reabsorbed into the potting soil.

You will also need to get some more potting soil. I do not recommend using ordinary garden soil as potting soil. It is usually too poorly drained for use in a pot and may come with extra things you don’t want like weed seeds, insects, worms, and pathogenic fungi or bacteria that can make your plant sick.

Remove the plant from the old pot. If it seems to be stuck, try tipping it upside down and tapping the rim of the pot on a counter. Place some potting soil in the new pot and check the depth by setting the plant in the pot. When finished you will want about an 1” of open space left at the top of the pot for a 6-8” pot or about 2” of open space left for larger plants. This extra space will hold water while watering and allow it to soak down into the potting soil. When you have the right depth, continue adding more potting soil, firming it around the old root ball. If you don’t firm it well enough, the water will just run down around the old root ball instead of soaking into the old root ball and new potting soil that you added. Give the plant a good thorough watering, so that you see water coming out of those drainage holes. Let it drip out then replace it back in your home for additional years of life and growth.

Do You Have Gardening Questions?

You can submit your gardening questions to the Ask-an-Expert section of the website in the “Gardens – Gardening”. There you will be able to type in your own question on the Ask-an-Expert portion. An Extension horticulture professional or a Master Gardener will reply to the question, in most cases, within 48 hours. Then an email alert is sent to you, with a link to the personalized answer. I personally check this website for incoming questions and provide answers when I can. If you would like one of your questions to be included in this iGrow Gardens column, just include “Farm Forum” at the beginning of your question so that I will be able to see that you might like to see your question show up in the column. I will check the site and use some selected questions and answers in upcoming columns. While you are on the iGrow website, check out all of the other great resources that are there for you to use, not only for gardens but also for many other areas of agriculture production.