What To Do This Month Today is officially the first day of winter. If you haven't already dug out your old sheets and rounded up the clothespins, now's the time. It's been a colder than usual November and December so be ready for more of the same. Protect tender plants (those that suffer when temperatures drop below 35 degrees) by covering with sheets or frost blankets (no plastic). Be sure the covering extends all the way to the ground and is anchored there to trap heat radiating from the soil. For tender trees too tall to cover, try wrapping the trunk in holiday lights. Troubleshoot houseplant problems: Brown leaf tips or margins mean too much fertilizer, dry soil or low humidity. Thin new growth or yellowing older growth means too little light. Wilting and yellowing mean too much water or poor drainage.Transplant trees and shrubs. Keep them well-watered until they're established. What To Plant This Week Give yourself a little spring boost by starting petunias, pansies and snapdragons from seed. If you're reusing containers, clean them with a bleach-and-water solution and fill with potting mix. Plant the seeds, moisten, cover with clear plastic wrap and set the pots in a sunny window till the seeds sprout. Then remove the wrap, move them outside and fertilize weekly till they're ready for transplant. Perennials: blue salvia, chrysanthemum, coreopsis, day lily, gaillardia, gazania, Shasta daisy, Stokes aster, yarrow.