Keep Tomato Plants Healthy and Happy

At this point in the season, tomatoes are either doing great or tipping toward disaster. So in addition to offering some growing tips to help make tomatoes happy and healthy, I’ll explain some of the common things that can go wrong.

Probably the most important thing you need when growing tomatoes is sunlight—8 hours or more is best, but 6 will allow plants to produce a fair amount of fruit. If you don’t have a spot that gets even 6 hours of sun and someone is home a lot during the day, consider buying a few round, rolling plant stands. I got mine (which look like metal Frisbees on wheels) at Ikea, but most garden centers sell them now, too. Put your tomatoes in large pots, set them on the rolling plant stands and move them into the sun as it moves throughout the day.

Soil is key to tomato success too. They thrive in healthy soil, so it’s a good idea to work some compost and composted manure into the area before planting. If you’re planting in pots, just add those things into your potting mix. Halfway through the season, scratch a little more compost into the top of the soil around plants, but don’t add more manure. Too much nitrogen (N) will give you lots of leaves and little fruit. You want a fertilizer with more potassium (K) than nitrogen in it. Phosphorous (P) can also be on the low side, usually, since compost supplies a good amount of that. Product labels always show the N-P-K ratio like this: 10-10-10 or 5-2-1. You want something more like: 1-0-4 or 1-1-3. Seaweed (powdered or liquid kelp) is a great choice and is usually 1-0-4.

Tomatoes like water, but not too much. Water plants deeply but not so often, or so much, that you end up with soggy soil. That can lead to disease problems and, later in the season, to tomatoes that don’t taste like much because all that water got channeled into the plant’s fruit. If you’re growing tomatoes in pots, stop watering when you see water running out of the bottom of the pot. Watering consistently, every few days in hot weather—more often if plants are growing in pots—will also help prevent the dreaded blossom end rot. You know you have this common problem when your tomatoes have black spots on their bottoms. Consistent watering allows the fruits to get the calcium they need from the soil to develop properly.

Did you bury the stem at planting time? If not, do that next year by gently plucking off the plant’s branches below the top flush of leaves. Depending on the size of your transplant, you’re usually burying 2 to 6 inches of stem, and that’s a good thing because new roots will sprout all along that stem and help your tomatoes be strong and healthy.

Pruning tomatoes doesn’t need to be as complicated as it is often described. Tomatoes are classified by growth habit: determinate tomatoes—also called bush tomatoes—are bred to be more compact, usually about 4 feet tall while indeterminate varieties—also known as climbing or vining types—can grow to 6 feet tall or more. Determinate tomatoes don’t need much pruning beyond removing all of the suckers below the first flower cluster. Indeterminate tomatoes benefit from some pruning, but you don’t need to grow crazy. Basically, if you pinch out suckers and pare plants down to around stems, you’ll get bigger fruit and less sprawling growth. If you let plants be more unruly than that, you’ll get more fruit but you’ll have to deal with a more tangled mess of vines. Either way if fine, so don’t sweat it a whole bunch.

Are the leaves on your tomato plants curling up in hot weather? Don’t worry, that’s probably not a disease. It’s just how some tomato varieties react to the heat. This type of leaf roll usually starts on lower leaves and works its way up. It doesn’t look great, but it shouldn’t affect fruit development. Watering regularly and mulching the ground beneath your tomatoes can help keep this problem at bay.