It’s never too late to get started. May is a great month to feed trees and plant bulbs.
Since you didn’t fertilize trees and shrubs in April, it is not too late in May. Deciduous shrubs and trees can use a good all-purpose garden fertilizer (10-10-10). Use evergreen fertilizer for acid-loving plants like rhododendrons and azaleas.
It’s also the right time to plant the fun stuff like summer flowering bulbs such as dahlia, gladiola, begonia, lilies, and canna. With gladiola, plant bulbs every two weeks until the first of July. The new flowers will provide you with vigorous color until frost.
Summer perennials can be set in during May, too. Try phlox, daylily, carnation, and primrose. But wait until later in the month to plant annuals.
You never know about May. The weather can change quickly and, in some zones, a sudden frost can even wreck your garden plans. So watch the weather carefully and be prepared to cover your plants if necessary.