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Lisa Yankowski is part of the team of gardeners that answers your questions. Contact the team on the Ask A Gardener page.

Gardeners have questions — and we have answers. Whether you're planning your first garden and have questions about design, or you've been gardening for years and need ideas for dealing with a persistent pest, ask your question on the Ask A Gardener page.

Questions from our customers inspire new articles, blog posts, Facebook discussions and innovative products. You'll find some of the most frequently asked questions answered below:

I have some old seeds. Should I try to sow them or should I assume they're no good? Although seeds are packed fresh each year, you can often get good results from seeds that are several years old. To decide if it's worth planting them, do a simple test.

The first step is to put 10 seeds in a damp paper towel and nestle it in a plastic bag for a few days — preferably in a spot that's about 70 degrees F. — or warmer.

Most seed packets will tell you "days to germination." After the expected number of days have passed, check to see how many sprout. If you get more than 50 percent germination, you might want to give it try, planting two or three seeds to a cell. If nothing sprouts, all you've lost is a paper towel and 5 minutes.

Some types of seed are good for four to five years, but others are more perishable.

I was told to bury a portion of the stem when planting tomatoes. Is that right? Yes. It's a good idea to bury about 6" of stem. Just remove the leaves from the portion to be buried and plant it deep. When buried, tomato stems will sprout roots, resulting in a healthier, sturdier plant. Get details on this technique in our slideshow: Step by Step: Growing Tomatoes from Seed to Harvest

What's the right kind of soil for my new raised bed? For most situations, we recommend these proportions:

• 60 percent topsoil
• 30 percent compost
• 10 percent soilless growing mix that contains peat moss, perlite and/or vermiculite, such as Transplant Mix or Container Mix

To calculate how much you need, use the Soil Calcluator. Keep in mind that proportions are approximate because soil volume varies from source to source. For instance, if the calculator specifies .444 cubic yards of soil for your bed, go ahead and round it up to a half yard.

Why are my seedlings so spindly? Weak, "leggy" growth is often the result of inadequate light, both in intensity and duration. Place seedlings under grow lights, arranging them so the lights are a few inches above the tops of the plants, and keep the lights on for about 14 to 16 hours per day. For more information, read the article How to Start Seeds.

Onion seedlings

Should I plant onion sets, or start from seed? Sets are a good choice if you want scallions (green onions), but you're not likely to get large onions. Though it might sound unlikely, you'll get bigger onions if you start from seeds and seedlings. Learn all about it in Onions 101.

Can I throw coffee grounds in my compost? Coffee grounds are a fine addition to your compost, which depends on a mix of "green" (nitrogen) and "brown" (carbon) ingredients — about 3 parts brown to 1 part green. Despite their brown color, coffee grounds are "green," and a good source of nitrogen at a time of year when there's little green. For more information, read the article Compost Your Coffee Grounds.

Blanket flower (Gaillardia x grandiflora) is one of many perennials that are easy to grow from seed.

Can I start perennials from seed? Yes, many perennials are easy to start from seed. Examples include coreopsis, dianthus and blanket flower. Some will bloom the first year if you give them a head start by sowing the seed indoors in early spring. For more information, read the article Grow Perennials from Seed.

Can I just plant the garlic I get from the grocery store? You could, but supermarket garlic is not always the most flavorful, and it might have been treated with an anti-sprouting agent, so it might not grow well. It's better to buy garlic that's grown for planting. You'll find dozens of varieties, from spicy to mild. You can choose hardneck or softneck types. Softneck garlic is good in mild climates because it matures more quickly. Hardneck varieties tend to be more hardy, and they produce the edible scapes that some folks enjoy.

Once you harvest your first crop, you can save some for replanting. The largest cloves will yield the largest bulbs.

The Organic Garlic Collection includes at least a half pound of hardneck and softneck varieties, which will produce enough garlic for an average family of four. For more information, read Planting and Harvesting Garlic.

How long should I water? It depends on many factors: soil type, recent rainfall, weather conditions and more. To make sure your plants get enough water, check the soil with your built-in "moisture meter": your finger. It's better than any other tool. The soil should feel cool and moist at the root zone. A timer makes watering easy; just adjust the frequency as weather conditions change. For more information, read the article When to Water.

I have no fruit out; why do I have fruit flies? Look for spilled juice; also, cover your compost pail, rinse empty bottles in your recycling bin, cover ripening fruit (especially bananas) and, of course, get a fruit fly trap. For more information, read the article Fighting Fruit Flies.

Can peonies be divided? Yes. Unlike most perennials, peonies rarely need to be divided. The only reason to do it is to get more plants — or share them with friends. It's best done in the fall. Dig up the clump and use a sharp tool to divide it into sections, keeping three to five eyes in each division. Be sure to water the transplants thoroughly, unless you get plenty of rainfall. Keep in mind that divisions (and transplants) might not begin blooming again for two or three years. For more information, read Peony Care.

How do you take care of rhubarb in the off season? Rhubarb grows in cool weather — spring and fall — and goes nearly dormant in the summer, especially in hot weather. General care: fertilize in early spring, remove all flower stalks as they appear, pick off yellowing leaves as the plants go dormant in summer. After fall frost, remove and compost the mushy leaves, then add some compost or composted manure to the soil around the plants. For more information, see the entry on Rhubarb in the Vegetable Encyclopedia.

How do I get really blue hydrangeas? To encourage blue hydrangea flowers, grow the plant in soil that has a pH of 5.2-5.5. If your soil is more alkaline, you can lower the pH by applying Soil Acidifier at the rate specified on the package. Soil pH can also be lowered (more gradually) by applying an acidic organic mulch, such as pine needles or pine bark.

A lacecap-type hydrangea.

If the pH of your soil is naturally quite high (alkaline) it will be very difficult to get blue flowers — even if there's plenty of aluminum in the soil. Alkaline soil tends to "lock up" the aluminum, making it unavailable to the plant. However, you can grow fabulous pink hydrangeas.

More information: How to Grow Blue Hydrangeas, which explains the issue in more detail. There are many types of hydrangeas and not all of them can be made to produce blue flowers.

Colorado potato beetle. Photo: David Grist

What should I do about the beetles on my potato plants? Those are Colorado potato beetles, a pest that causes a lot of trouble for people who grow potatoes. Because of their distinctive striped bodies, adult beetles are easy to identify — and control: Just pick them off with your hands and toss them into a bucket of soapy water. The beetles might bother your plants for a few weeks; just keep monitoring and hand-picking and your plants will be fine.

If you plan ahead, you can shut out the beetles with garden fabric or Pop-Up Covers.

Tip: Before you see the beetles, look for the bright yellow eggs, which you'll find under the leaves. Rub them off with your finger.

More information: Controlling Colorado Potato Beetles.