Carefully divide perennials
for better growth.

Dividing Perennials -- Divide most perennials once they've sent up significant foliage at least a couple of inches tall. Divide them if they are getting crowded (floppy stems, reduced blooms, a dead spot in the middle) or you simply want more plants. Sedum "Autumn Joy," for example, needs to be divided about every other year to prevent flopping. Siberian irises usually need dividing every three years or they start to grow in a circle around a dead center.

Dividing Perennials

Deadheading 101 -- Deadhead spent flowerheads on spring-blooming bulbs to direct their energy back to their roots so they can build vigor for next year.

Deadheading 101

Planting Bare-Root Trees, Shrubs, and Roses -- Continue to plant bare-root trees and shrubs as well as bare-root roses.

Planting Trees and Shrubs

Planting a Bare-Root Rose

Planting Trees and Shrubs -- Continue to plant container-grown trees, shrubs, perennial herbs, and perennial flowers

Planting Trees and Shrubs

• Plant pots, windowboxes, and containers with cool-season flowers that can withstand frost and even snow. Pansies are a favorite. Or, tuck in pots of purchased forced spring-bulbs, such as tulips or daffodils, which are available at supermarkets and garden centers now, to brighten these spots.

What to Plant -- Plant perennial fruits and vegetables, including strawberries (keep the blossoms pinched off the first year so they develop strong roots), rhubarb, raspberries, asparagus, and other perennial fruits and vegetables now. You can also plant potatoes.

Strawberries

Pruning Roses -- If you haven't already, prune roses once signs of growth are well underway -- the red leaf buds have started to swell and just barely started to unfurl.

Pruning Roses

• Prune evergreens any time from now until late summer. (Don't prune later than that or you'll prompt new, tender growth that will get zapped by winter's cold.)

Pruning -- Finish up most pruning this month with the exception of spring-blooming trees and shrubs. You can prune them immediately after they're done flowering.

Pruning

Last Average Frost Date -- In the coldest northern regions, you can still plant cool-season crops, including seeds for radishes, peas, sweet peas, lettuces, and other greens, and seedlings for broccoli, cauliflower, and cabbages. In warmer regions, the last average frost date is this month. That means gardeners in those regions can go ahead and plant warm-season annuals (tomatoes, peppers, basil, marigolds, petunias, and the like) since all danger of frost has passed.

Last Average Frost Date

• Wait to plant seeds for corn, green beans, squash, cucumbers, okra, sweet potatoes and other heat-lovers until the soil has warmed to 60 degrees F. That's warm enough for you to walk on it comfortably barefoot.
• Start fertilizing roses, which are heavy feeders. Decide on which plan of attack you want to take. Some gardeners feed every two weeks until August with a liquid fertilizer. However, a lower-maintenance approach is to work a slow-release fertilizer (or compost) in around the shrub according to package directions, usually every 6 weeks or so. Some rose fertilizers include a systemic pesticide, so you can feed and prevent pests at the same time. However, these pesticides also can kill butterflies and beneficial insects, so beware. Consider organic feedings, which would mean working in a spadeful of compost around the base of the plant every month or using a fish emulsion fertilizer.
• April is a good time to aerate your lawn. Most lawns should be aerated every two or three years to alleviate compaction and reduce thatch. You'll need to rent a machine that takes out plugs of soil or have a lawn service do it. (As an alternative, fall is also a good time.)
• For the greenest, lushest lawn, apply another application of fertilizer to your lawn late this month or early next.
• Early this month, if desired, apply a pre-emergent weed killer to beds and borders. It will greatly reduce weeds later on. However, it works by preventing seeds from germinating, so don't apply anywhere you're planting seeds.
• Clear out debris and muck from the bottom of the water garden and add it to your compost heap. Start feeding fish again when water temperatures hit 50 degrees F or they're active and eagerly eat the food.