Q: I have a question about planting garlic. I read in your book ("Golden Gate Gardening") that you recommend getting the bulbs at the nursery. Is there something wrong with getting organic garlic at a grocery, checking for freshness and then planting those?

A: The reason I suggest that you buy garlic at a local or mail-order nursery is that nurseries usually offer disease-free garlic starts. Garlic gets awful diseases that rot the bulbs, rendering them inedible, and you don't want to introduce them into your garden soil if you can help it. Two garlic diseases, white rot and lettuce drop, if introduced, can lurk in the soil for years. White rot has devastated the once-thriving garlic region near Gilroy.

Organically grown crops are not the same thing as certified disease-free. An organically grown field could have had some degree of damage from a plant disease, but the produce that survives may look fine even though it carries a few disease spores. (For purposes of eating, this is not a problem, since eating a few garlic-disease spores will not harm you.)

It comes down to trust. If you talk to a farmer at a farmers' market and trust their word that they have not had any problems with garlic disease, perhaps you can have a measure of confidence. At a grocery, where you can't talk to the grower, not so much.

Even growing certified disease-free garlic, you may experience some losses. In May of one year, I had large, healthy, almost ready to harvest garlic from nursery-purchased bulbs, then a late rain fell and the entire crop keeled over with rotting bulbs. Where did the disease come from? I can't say. I might have escaped it by suspending a tarp over the plants during the several rainy days. I will not plant garlic in that bed for a couple of years, and hope it's a short-lived disease.

To minimize the chance of disease, stop watering your garlic as soon as the lower leaves begin to turn yellow, usually sometime in May, and keep the soil dry until you harvest when at least 60 percent of the leaves are brown. If you are using a drip system, locate the garlic where you can pull the drip lines back.

The best time to plant garlic in the Bay Area is October. The second best time is in February, though the heads made by February-planted garlic may not be quite as big. The soil is so cold in December and January that garlic planted then may have a hard time getting going, and the combination of cold and wet soil may cause it to decay before it starts to grow. Whenever you plant it, set the cloves pointed-end up and about an inch under the surface. Don't water the day you plant. When you see the green shoots poking above ground, water the first time.

Q: I'm going to try planting potatoes this year. However, I don't know if I have room to plant all of the seed potatoes this spring. Can I save some of them for planting later in the year?

A: Potatoes for planting can be stored in the refrigerator for several months to plant later. Store them at 40 degrees Fahrenheit or a couple of degrees below or above. Avoid storing them near apples, which give off a gas that will promote sprouting. Check them periodically for decay.

Take potatoes out of the refrigerator for a couple of weeks before you plant them and keep them at room temperature. To encourage sprouting, you can cover them with a piece of damp burlap during this time. If the potatoes are sprouting, plant them when sprouts first emerge, before they elongate.

Potatoes sold for planting are known as "seed potatoes." These days, many are sold as small tubers meant to be planted whole, rather than, as in the past, cut into pieces first. In the Bay Area and nearby, we needn't wait until the traditional Irish St. Patrick's Day planting time, but can plant them starting in mid-February. (For more on potato planting and care, see my book.)

As with garlic, it's best to purchase certified disease-free potatoes to avoid potato diseases, although spores of one disease, potato/tomato late blight, can blow in from nearby gardens to infect otherwise healthy plants. Some varieties, such as 'Kennebec' and 'Russian Banana,' show some resistance to this disease. These varieties are fairly easy to find, including at Potato Garden (potatogarden.com; (800) 314-1955), which also carries one of the widest selections of seed potatoes around.
