Planting Trees and Shrubs -- Continue to plant container-grown trees, shrubs, perennial herbs, groundcovers, and perennial flowers. However, in the desert, finish planting this month.
Planting Nursery Plants -- Continue to plant warm-season annual flowers and vegetables (tomatoes, peppers, marigolds, petunias, and the like) as long as all danger of frost has passed and as long as you have enough time for them to beat the summer heat. (However, in hot desert areas, for example, that means no later than late February.) If in doubt, give a quick call to the garden center nearest you.
Deadheading 101 -- Deadhead fading flower blossoms. You'll keep your garden neater and flowering better longer.
Stakes and Supports -- Stake tall plants that will need it now while they're just a foot or so high.