Q: We'd like to plant some trees this spring. How can we tell when the ground is ready?

A:You'll want your soil to be warm enough and dry enough, says Yvonne Carree, UI extension forestry associate. It's warm enough when its temperature is at least 40¡F 4 to 5 inches below the surface. To determine if it's dry enough: Dig a hole about a foot wide and a foot deep, then fill it back in. If you can't refill the hole completely, planting conditions are too wet. Working wet soils invites compaction, so hold off until the soil is drier. On the other hand, if you have too much soil left, it's too dry; go ahead and plant, but water your new trees immediately. "If you fill the test hole and have a couple of handfuls of soil left over, the moisture is just right for planting your trees," Carree says.

Dig your hole; if there is too little soil to fill it back up, the soil is too wet. If there is too much, it's too dry; be sure to water! (illustrations by Melissa Rockwood)

Q: What are gnats doing in our house in the dead of winter?

A: If what you've got are slender, fragile, grayish flies no longer than 1/8 of an inch, they're fungus gnats. According to Bob Stoltz, UI extension entomologist, they feed on decaying organic matter in your houseplants' potting soil. Other than being truly annoying by flitting around our noses and eyes, they're no threat to us or to our plants. Stoltz suggests several responses: (1) tolerate them, (2) keep the potting soil a little bit drier, (3) treat your houseplants with the biological control agent Bacillus thuringiensis var. israelensis, or Bti, (4) apply parasitic, beneficial nematodes, or (5) use an insecticide labeled specifically for houseplant soils.

Q: What are the most common mistakes backyard gardeners make when growing potatoes?

A: The first is their choice of variety, says Steve Love, UI potato variety development specialist. "Here in Idaho, we love that Russet Burbank potato, but it doesn't usually grow well in situations where we're managing conditions for many different crops. Instead, choose something like Frontier Russet, Nooksack, Gem Russet, Red Norland, or IdaRose." The second mistake: Getting your seed from the wrong source. Never use potatoes from last year's garden or the grocer's shelf. They could carry plant viruses that will sicken your crop. In addition, many grocery potatoes have been treated with a chemical that prevents sprouting. Instead, buy "certified" seed from a nursery, garden supply store, or seed grower. Third: Cutting seed pieces too small. "A good rule of thumb is about 2 inches long and almost as wide. Each piece should have at least one eye--and two or more is better," says Love. Fourth: Ignoring the late blight fungus, which attacks garden potatoes (and tomatoes) as aggressively as commercial crops. If and when late blight strikes your area, start spraying with a good fungicide on a weekly basis.

Q: I'm gardening on the cheap: Can I use last year's containers to start seeds indoors and still avoid damping-off fungus?

A: You sure can, says UI horticulturist Bob Tripepi. Almost any container that provides good drainage can be used for planting seeds: wooden boxes, plastic flats, metal containers, or pots made of clay, pulp, or styrofoam. First clean them thoroughly, then soak them for 10 minutes in a solution of 1 part chlorine bleach to 9 parts water, and finally rinse them in clean tap water. If the containers don't have drainage holes, drill two to four in the base; the larger the pot, the larger the holes should be. An alternative method being used at the university's forest nursery is to completely submerge the pots in 175° to 180°F tap water for 1 minute. Nursery manager Dave Wenny says it works just as well as bleach.

Q: What are the secrets of growing good strawberries? So far, they've escaped me!

A: Location, location, location! Choose a well-drained, weed-free site that gets at least 8 hours of sun daily. Raised beds and containers work great. Then, select varieties that are winter-hardy for your area from the UI's list of recommended strawberries (Bulletin 739, Berry Varieties for Idaho). Keep rows no wider than 12 to 18 inches and thin plants to 6 inches apart. To keep fruit clean and reduce weeds, spread clean straw under the plants and in alleys. If possible, use drip irrigation and keep soil moist but not waterlogged. If you must use sprinklers, water early in the morning to reduce the threat of diseases. After several hard frosts, mulch your strawberry beds with 6 inches of weed-free straw. Remove the straw in early spring before new growth starts.