Tomatoes are as close as any vegetable gets to growing like a weed, yet problems occasionally arise.

Take, for example, that large blackened area that you sometimes see opposite the stem end of a tomato fruit. That’s blossom end rot, which occurs when the fruits do not get enough calcium. This means that your soil needs more calcium, which you add when you lime your soil to lower its acidity, or that your plants need a more even supply of water, which carries calcium through the plants. Mulching and, of course, watering are ways to even out soil moisture levels. Also, temper your use of fertilizer, or rampant leaf growth will suck up water and calcium at the expense of the fruits. Don’t toss away those blackened fruits, though, because the red part of each one tastes just fine.

Another problem you often see is cracked fruit. The cracked fruits are always ripe, so try to find and eat them quickly. Tomato varieties differ in their tendency to crack, and mulching helps here also.

If healthy leaves are being stripped from your tomato plant, tomato hornworm is at work. This big, fat caterpillar is hard to find because its color exactly matches that of tomato leaves. Leave any insect alone that has rows of ricelike grains on its back. Those are eggs of a parasite that will soon kill that caterpillar, then seek out other victims.

Crush any hornworms that aren’t parasitized or spray with a biological insecticide containing the Bacillus thurengiensis, which doesn’t harm most other living things.

A widespread problem of tomatoes this time of year is yellowing and loss of leaves, beginning with those nearest the ground. Leaf spot diseases, the cause, lead to early demise of the plants and sunburn of fruits once shaded by leaves.

Control these diseases by thoroughly cleaning up and composting all tomato leaves, stems, and fruits at the end of each season. And each year plant tomatoes as far as possible from where you planted them the previous year. Also mulch the ground to reduce the number of spores splashed up onto plants from any debris overlooked in the previous year’s cleanup. As a final line of defense, plant tomatoes in an airy, sunny spot where leaves will quickly dry.

Fruits that are catfaced, rather than smooth and round, could be the result of poor pollination. Then again, some delectable old varieties, such as Belgian Giant, are just naturally “catfaced.” Eat them with your eyes closed.

Tomatoes are as close as any vegetable gets to growing like a weed, yet problems occasionally arise. A widespread problem of tomatoes this time of year is yellowing and loss of leaves.