I planted tomatoes for the first time last year. When they finally started to ripen, I found quite a few of them had some kind of rot on the bottom about the size of a quarter (or a little more). What caused this and how can I avoid it this season?

– Laura Atchley, Roseville

According to UC Master Gardener Bill Pierce, your tomatoes had blossom-end rot. This is caused because the plants have failed to take up sufficient calcium from the soil because they were either over- or under- watered.

Some varieties such as Ace and Roma are prone to this problem. The so-called "rot" is just dry tissues on the blossom end of the fruit; this can be cut off and the fruit can be eaten.

The problem usually affects just the first fruit set. This year, water your new plants only when the top 3 inches of the soil are dry.

As your plants grow, deep- water them once a week. Begin by wetting the soil to a depth of 6 inches; gradually increase this so that when the plants are about 15 inches tall, you are wetting the soil to a depth of 18 to 24 inches. Continue to wet to this depth for the remainder of the season.

Also, apply a 4-inch layer of mulch to your tomato bed. It will help keep the soil cool and evenly moist.

For additional information, send a self-addressed 44-cent, business-size envelope to Publication No. 8159, UC Cooperative Extension, 4145 Branch Center Road, Sacramento, CA 95827.

Last summer, we planted several tomato plants. We grew two different varieties and both had hundreds of tomatoes, but none of them seemed to turn red – even after a month or more on the vines. In September, we were still waiting for red tomatoes.

I'm not sure what variety they were because we lost the markers, but one might be "Ace." I added chicken manure before planting; I wonder if that may have given them too much nitrogen.

The plants were very big and healthy and, as I said, bore hundreds of baseball-size fruit, but all green. Our vegetable garden gets full sun until about 4 p.m. each day. Do you have any suggestions?

– Keith Gentz, Lincoln

The cool weather last summer delayed the ripening of nearly everyone's tomatoes, according to UC Master Gardener Bill Pierce.

Your site is correct for a good crop. This summer will probably be more normal and the fruit should mature rapidly.

Note: Tomatoes need warmth (nights and ground temperature above 50 degrees) and sun (seven hours a day or more) to produce fruit. Most tomato varieties need 40 to 50 days after blossom set to ripen on the vine, but cold and cloudy days can lengthen that period significantly, as we saw last summer.

Excessive hot weather can be a problem, too. When temperatures climb above 85 degrees, tomatoes won't ripen, either.

Heavy fruit set also can work against ripening the crop. Turning all that fruit red takes a lot of plant energy and tends to delay the whole crop.

Come September and you again have a ton of green tomatoes (but no red ones), try removing some of the mature green ones. (They've begun to turn a lighter green and are good size.) That will help the plant channel its energy into ripening what's left on the vine.

Meanwhile, those green tomatoes can be ripened in an open cardboard box, kept at about 70 degrees. It takes about two weeks for them to ripen off the vine.

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