Tomatoes are one of the most popular crops among home gardeners – in our neighborhood, it seems like every other house has at least a couple of tomato plants in the yard. Every year, I look forward to late summer and weeks of BLTs and caprese salads! But this is also the time of year when hot weather and common diseases can start to make your tomato plants look a little rough. Read on for advice on growing tomatoes in the home garden, including tips on plant selection and avoiding common disease and cultivation problems.
If you’re looking out your window at sad, wilted tomato plants with yellowing leaves, rest assured – you’re not alone! Minnesota’s hot, humid summer climate is very conducive to several tomato plant diseases that tend to pop up every year. Early blight, Septoria leaf spot, and bacterial spot are all very common and cause similar symptoms. You may see yellowing leaves, especially towards the bottom of the plant, or yellow and brown spots on leaves or fruit. Although these diseases are caused by different pathogens (including bacteria, viruses, and funguses), we deal with them in similar ways. The pathogens are generally spread when the plant’s leaves come into contact with contaminated soil, such as when water splashes the soil onto leaves. A lack of air flow in dense tomato plants can also be an issue.
Once a tomato plant has one of these diseases, there is generally no way to cure it. However, removing diseased foliage and trimming off some branches to improve airflow throughout the plant can slow the disease down and hopefully give you enough time to harvest some tomatoes.
There are also several tomato disorders that commonly vex Minnesota home gardeners. These are not caused by pathogens, but by environmental factors like watering and weather. Blossom end rot is one of the most common tomato disorders, and causes a tan or black “rotten” spot on the fruit opposite from the stem end. This is the result of a calcium deficiency, which weakens the fruit’s cell walls – but don’t add calcium to your garden just yet! Most soil throughout Minnesota has plenty of calcium in it, but the plant may not be able to absorb the calcium in the soil. The most common issue that reduces calcium uptake is inconsistent watering. Make sure your tomato plants are watered consistently and stay moist but not too wet. And don’t worry too much – often, the first tomatoes produced by a plant will be affected by blossom end rot, but later tomatoes will be fine. Another factor that can cause insufficient calcium is applying too much nitrogen fertilizer, which causes the plant to grow very quickly. This can cause blossom end rot when the growing plant needs more calcium than its roots can absorb. If you have a lot of problems with blossom end rot, consider having your soil tested to determine whether you do have a calcium deficiency in the soil.
Other tomato problems can arise from a wide variety of factors, including heavy rain, high temperatures, low temperatures, sun scalding, damage to tomato flowers, damage from insects, and damage from herbicides applied nearby. There’s not enough room in this column to discuss the many potential pitfalls, but you can visit the University of Minnesota Extension website for detailed advice on lots of tomato problems!
When you plant tomatoes next year, there are a few things to consider that can help reduce the likelihood and severity of problems. First, you can look for disease-resistant tomato varieties, which will be labeled in a seed catalog or online. I’ve had good luck with the variety Juliet, which is resistant to early blight, and Galahad, which is resistant to several common viruses. Also, consider adding mulch beneath the plants to reduce the likelihood of soil splashing onto the leaves. Another option is to use self-watering planters or drip irrigation for your tomatoes, which has the added benefit of ensuring consistent watering to reduce blossom end rot.
Finally, make sure to space your tomato plants out when planting them to improve air flow and reduce fungus and bacteria problems. Although the plants look so small in the spring, don’t plant them too close together – remember that they will get much, much bigger! You can also remove some lower branches, which allows more air to move around the plant and keeps tomato leaves away from the soil.
For more information, check out the University of Minnesota Extension Yard and Garden website. Extension resources are written by experts, and contain the latest and most reliable research-based information. Happy gardening!
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