Q What should I look for when I'm buying garden seeds? Are some catalogs better than others or do they all get their seeds from the same source?

A Some well-known seed companies grow some or all of their own seeds, while others buy seeds from a number of producers, then repackage them with their brand name. Either way, it should make no difference to you. If you're looking for a particular cultivar -- such as an Early Girl tomato -- the seeds will be identical regardless of which seed company you buy them from.

What you should pay attention to is how fast-maturing the seeds are. Because we have a relatively short growing season, you should look for seeds that mature and produce their flowers or vegetables sooner rather than later. Seed packets and catalog descriptions should include the number of days to maturity.

There also will be information on the amount of seeds contained in a packet, either by weight or, in the case of large, new or unusual seeds, by the number of seeds. Some seed packets might offer better value, but don't buy the bargain-sized packages unless you can use most of the seeds or share them with another gardener.

The percentage of seed germination (or viability) in new seed packets is governed by law, as is seed purity. But when seeds are stored, even if they're stored properly, most will only be good for two or three years. And even then, fewer of them will germinate.

Troubleshooting tomatoes

Q Last year my tomato plant developed mottled patches on its leaves. It only produced two tomatoes and they rotted. How can I prevent a repeat of the problem this year?

A It's most likely your plant suffered from tobacco mosaic virus.

This disease affects tomatoes and their relatives, including peppers, eggplants and a number of other vegetables, ornamentals and weeds. Infected tomato plants produce few fruits, which are abnormal.

Tobacco mosaic virus infects a plant when it enters through a wound or break in the tissue. Often, the plant can be infected when it's handled as a seedling or transplanted, but it also can happen later.

Smoking or using tobacco products that are infected with the virus can transmit the virus to your hands, allowing you to unknowingly transmit the virus to your plants. It also may be transferred by insects that feed on infected plants, then move on to healthy ones. Unfortunately, the virus can survive for years in infected plant debris in the soil.

There is no spray or dust that will help ward off or treat tobacco mosaic virus once it's in your garden. Keeping your garden clean is your only option. Here's how:

• Dig out and destroy any plants that begin to show symptoms of the disease. Be particularly careful to remove all underground plant parts, not just the tops.

• Disinfect any tools that come in contact with diseased plant parts.

• If you smoke, always wash your hands thoroughly before handling plants.

Deb Brown is a garden writer and former extension horticulturist with the University of Minnesota. To ask her a gardening question, call 612-673-9073 and leave a message. She will answer questions in this column only.