Spring Planting


Let the Planting Begin!

The beautiful days of spring have arrived in Missoula and it’s time to plant the vegetable garden.  With the warm, sunny days it’s tempting to put everything in the ground now, but heat loving plants like tomatoes, peppers, squash, basil, and eggplant must wait for even warmer weather. The typical last frost free date in Missoula is May 20th. What does that mean for planting the garden?

Plants and seeds are sensitive to temperature and not just the air temperature we often discus when we say, “It’s a lovely 70 degree day.” Seeds are sensitive to soil temperature too – many seeds will only germinate within a set temperature range. For example, squash and pumpkins prefer soil that has reached 60 degrees or so. If the soil is cooler, the seeds are likely to rot before they sprout.  Other seeds such as beets, peas, radishes, lettuce, kale, and Swiss chard happily sprout in soil that’s 50 degrees (or even less). These same plants are also “tough,” meaning they will tolerate colder air temperatures and even survive light frosts. 

Soil warms faster than air and un-mulched dark soil warms very quickly. Dirt is a good absorber of solar heat but Missoula’s cool spring nights can dissipate that heat rapidly. You can plant sets or seeds of heat lovers before the nights are warm, but you will need to mitigate the chilly nights with row covers, wall-of-waters, or a cold frame. I often plant green bean seeds before the air temperature is to their liking. In order to keep the sprouts from freezing, I use my wide-mouth quart and pint canning jars to cover the newly emerged plants. From a distance, my garden appears to be growing glass containers!  Other low cost plant covers can be made from plastic milk jugs – gallon or half-gallon sizes. Simply cut the bottom off the jug, remove the screw top, and place over the plant you want to protect. Do press the jugs in the soil about an inch or the wind is likely to blow them around your yard and beyond. One of the advantages of the milk jug “mini-greenhouse” is that if the day gets warm and you’re not around to remove the container, the open top allows hot air to vent rather than cook your plants.  A note of caution: if you use glass jars to cover your seedlings, be sure to remove them during sunny days as the sunlight will fry the plants underneath the glass.

 Air temperature is very important to any delicate or semi-delicate plants such as tomatoes and peppers. If you’ve grown your own sets or purchased them, they need to stay in your house or greenhouse until the air temperature remains above freezing, even at night. Tomatoes and peppers thrive when they’re warm or hot. They prefer warmer spring and summer nights than Missoula often has and benefit from cold covers until our very hottest days in July and August finally arrive.  Some of my best tomato and pepper crops have been grown in a tiny greenhouse or in wall-of-waters. Both the greenhouse and wall-of-waters keep the night and day temperatures consistent through the growing season. You can make your own “almost wall-of-waters” from empty half-gallon milk jugs. Rinse the jugs and fill with water, ring the tomato or pepper plant with six to eight jugs. During the day, the water in the jugs will gather solar heat and then release it during the night, providing your plant with a steady, warm micro-climate. Ringing your tomatoes with medium to large stones will do the same thing.

My general advice is to plant cold loving plants now if you haven’t already. Sow seed for radish, lettuce, kale, mustard, arugula, peas, Swiss chard, beets, turnips, rutabaga, and bok choi.  Plant sets (or seeds) of broccoli, cabbage, brussel sprouts, spinach, and onions. Plant your potatoes. Once mid-May has passed and Missoula is warm day and night, plant sets (or seeds) for tomato, peppers, eggplant, basil, squash, pumpkin, cucumber, watermelon, green beans, carrots, and tomatillo.  Mid-May is also a good time to sow another row or two of lettuce or other salad greens. If you stagger your salad greens plantings every two weeks through July, you’ll have fresh baby greens throughout the summer and into the fall.

Happy garden season everyone!