Tomatoes are the number one, most-loved homegrown vegetable in Minnesota. Summer is here, we have planted our gardens and now we wait for the bounty. But wait...... so much could go wrong between now and harvest time. Growing tomatoes in our Minnesota climate is an art and a science. We need to either start them early indoors and under lights, or purchase starter plants at a nursery because our season just isn’t long enough to plant seeds in the spring and get a good harvest before our first fall frost. I have, though, had small pear tomatoes reseed in my garden and make it to harvest before the first frost.
A little history on tomatoes:
First, they are a new world food. They originated in South America in the area now known as Peru and Ecuador where they were small red and yellow fruits. It was in pre-Columbian Mexico that they began breeding tomatoes and incorporating them into their food. The Spanish then introduced them to Europe. In Southern Europe they began to cook with them, while in Northern Europe, they were mainly grown as ornamentals. There was suspicion that they were toxic because they are in the nightshade family.
Tomatoes were introduced to North America in the 18th Century and were grown by Thomas Jefferson at Monticello. They are now eaten all over the world and each area has developed plants that grow well in their soil and climate and provide a taste that is preferred in their cuisine.
Tomatoes are a fruit though we generally eat them as a vegetable. Botanically they are classified as a fruit because they develop from a ripened ovary and hold their seeds inside. They are self-fertile, though they can cross-pollinate. If you want to ensure that your saved seed comes true, you should isolate your plants or bag the fruit. Incidentally, rhubarb is a vegetable, though we eat it as a fruit.
Most tomato plants are a vine and will continue to grow along the ground if not staked and pruned. These are the indeterminate varieties, and they are so-called because they will keep growing all season long. Some varieties have been bred to be determinate. These varieties will stop growing at about 2-3 feet tall and are good for growing in containers. They do not need to be pruned.
Plant your tomatoes outside when the soil has warmed, preferably on a cool, cloudy day. Tomatoes planted in cold soil will go dormant and take longer to recover and grow so don’t rush it. Not before mid-May for sure and you may want to check your soil temperature. When planting tomatoes, prune up the lower leaves and plant them deeply. The buried stems will grow roots to give you a sturdy plant. Check out this video on deep planting tomatoes: https://www.youtube.com/watch?v=KgumOvvfOY0
Put in your support right away so that you can train your tomatoes upward. You can feed them lightly now. Using a basic 5-10-5 fertilizer will work well. Mulch them to prevent disease and keep the soil moist. Straw is an excellent mulch to use around tomatoes. Water your tomatoes from below rather than overhead and water consistently if we don’t get rain.
Once you’ve planted your tomatoes it’s important to prune them. Try to prune them when they’re young, again two weeks later and then keep pruning as they grow. Ideally, you want to have one stem that may branch out into two. Keeping your plants pruned provides good air circulation and will give you larger fruit. Good air circulation helps to prevent disease. When we near the end of the growing season pinch off any new flowers that form. This will keep the energy focused on the existing fruit that may still be growing and ripening. https://hort.extension.wisc.edu/articles/tomato-pruning/
If the leaves on your tomatoes are curly and look dry it could be climate or weather related. The hot weather we are having means our tomatoes need more water. The plants will curl their leaves to preserve water and energy when it is too hot outside. When the temperature gets above 90° pollinators are not out. If we get a lot of 90° days, we may get less fruit due to lack of pollination.
Blossom end rot can be a problem in late summer. It’s caused by a lack of calcium, but the remedy is not to add calcium. Plants start to have difficulty taking up calcium from the soil when they experience uneven watering. Keep your plants evenly watered to avoid this problem. Some tomato varieties are more susceptible to blossom end rot than others.
Cracking, sunscald, and yellow shoulders are other disorders that can affect your crop.
Tomatoes need sun, plenty of space and air circulation. Over-crowding can foster disease.
Some of the issues that plague tomatoes are early blight, viruses, bacterial spot, and late blight.
These are explained in detail here: https://extension.umn.edu/vegetables/growing-tomatoes
There are so many tomato varieties available that it is sometimes hard to tell when they are ripe. In addition to our favorite red tomatoes, there are yellow, green and purple hues to deal with. A ripe tomato will easily come off its stem with a light twist. Now it’s time to enjoy your bounty. Tomatoes are great fresh, on a burger, a BLT, in a salad or in salsa. They can be preserved by drying, canning and freezing.
If you plan to can some of your tomatoes, be sure to follow a safe recipe. While tomatoes can be safely canned in a hot water bath, a pressure cooker should be used for salsas, soups and stews. Bottled lemon juice is recommended because different tomatoes have different levels of acidity. Safety is key and some of the methods and recipes used by our mothers and grandmothers are no longer considered safe.
Clean up all debris around your plants at the end of the season. Put the litter in your city compost. Do not compost these at home as a small compost pile will not get hot enough to kill bad organisms living in your plants.
Rotate your crop next year to minimize disease.
https://extension.umn.edu/yard-and-garden-news/early-season-tomato-sleuthing
https://www.winonapost.com/community/learn-from-the-masters-timely-tips-for-tending-tricky-
tomatoes/article_89caa174-87fa-46a9-9715-6559fcc6602f.html
https://crowwingmastergardeners.org/wp-content/uploads/2025/04/Plant-Guide-Tomatoes.pdf
https://nchfp.uga.edu
https://agrilifeextension.tamu.edu/wp-content/uploads/2025/05/Canning-Basics-Ball.pdf
submitted by Deb Reierson
June 29, 2026
University of Minnesota Extension Master Gardener