Q: I have a question about our tomato plants. I didn't notice it at first, but the leaves are turning purple. At first, I think it was just the veins of the leaves, but now the whole leaf is turning purple. We planted them early in hopes of getting fruit early, but so far there has been a few flowers and no fruit. They are in the same garden, but not the same location as tomatoes that grew fine last year and for several years in the past. We are new to vegetable gardening, but this doesn't look like a normal tomato plant anymore. What do you think is wrong?

A: There are several causes for purple leaves in tomatoes. Let's start with the most likely and work our way to the least likely.

When many plants don't get enough phosphorus, their leaves can develop a purplish cast that may not be detected right away. But if you look closely, you will see it. As the deficiency worsens, the purple color becomes more noticeable. Many times, there is plenty of phosphorus in the soil, but the plant can't get to it.

For tomatoes, this deficiency happens when the soil is too cold. Tomatoes are warm-season plants and one of the risks of planting them too early is that the roots will be stunted and the plant won't be able to get enough phosphorus. Adding more phosphorus through fertilizer won't help. As the soil warms up, the plant may begin growing normally and end up being fine. If it has been too cold for too long, the plant may not recover. The key parts of the diagnosis are early planting, cool soil, purple veins and overall purplish cast on the leaf. Even if the leaf is turning yellow, the veins will be purple.

If the weather is warm, the soil may be too wet from rain, poor drainage, too much mulch or a combination of these problems to cause root problems. If the soil doesn't dry out enough between rains, then there is not enough oxygen in the soil for healthy roots. If the roots are having a hard time growing, the top of the plant will show symptoms, such as the purple leaves not getting enough phosphorus. The Midwest has been getting so much rain that this can be causing these symptoms.

Beet curly top virus was discovered in the western parts of the United States in 1888. The virus is transmitted from weeds to crops by the beet leafhopper. It can infect more than 300 plant species, including beans, cucumbers, melons, peppers, spinach, squash and tomatoes.

BCTV symptoms include the leaf veins swelling, leaf curling, leaves turning yellow with purple veins, deformed fruit and stunting of the plant. If infected while small, the plant may die quickly. The curled leaves roll upwards, making the top of the plant look curly. Even though the tomato plant is not a preferred plant for the leafhopper, the virus is transmitted quickly to new plants. Some tomato varieties that exhibit some resistance to the virus include Columbian, Row Pac, Roza and Salad Master.

Beet leafhopper populations increase and decline in natural cycles. Some years they will be found everywhere and the destruction wide spread and in other years, there may be none.

The tomato purple leaf disorder, as it has been named in Florida, has caused concern in commercial growing areas. A cause has not been determined for this problem. The leaf area turns purple, but the veins stay green. Any portion of a leaf that is covered by another leaf or a tomato stays green. The purple leaf falls of prematurely. With fewer leaves, the plant becomes weaker and produces less. So far, this problem appears to be limited and not likely to be your problem.

One last possible cause is that some tomato plants naturally have a slight purple cast. The fruit may or may not be purple. You can look up your particular tomato variety to see if there is more information about the plant.

Email questions to Jeff Rugg at [email protected]. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.