- Check out clearance sales on garden supplies and plants. Don't buy sickly or leggy plants, but if a plant looks healthy, it usually is.
- Pull out lettuce that has "bolted," that is, it's sent up a long central stalk. It's gotten too bitter for good eating.
- You can remove yellowed, brown bulb foliage as soon as it pulls off without resistance -- no sooner!
- Dig up and discard tulip and hyacinth bulbs that performed poorly this year; for example, they sent up spindly leaves and stalks and few if any flowers. Most tulips and hyacinths only last 2-3 years and peter out after that.
- While your bulb plantings are still fresh in your mind, make a map or make other notations of where to plant what type of bulbs in the fall. This way, you'll know exactly what to buy and where to plant it and never accidentally dig up other bulbs again.
Last Average Frost Dates -- Plant seeds for corn, green beans, squash, cucumbers, and other heat-lovers once the soil has warmed to 60 degrees F. That's warm enough for you to walk on it comfortably barefoot, usually about two weeks after the last average frost date. If you've already planted corn, plant another crop or two every two weeks to help spread out the harvest.
Planting Trees and Shrubs -- Continue to plant container-grown trees, shrubs, perennial herbs, and perennial flowers. Finish up planting warm-season annual flowers, vegetables, and herbs, such as marigolds, coleus, fuchsias, tomatoes, and basil.
- Try planting your tomatoes under the eaves of your house. Research indicates that this may help keep the leaves drier and prevent tomato late blight.
Last Average Frost Dates -- A couple of weeks after your last average frost date, the soil has warmed enough to plant tender summer bulbs outdoors, including glads, cannas, and tuberous begonias. For a continuous supply of glads, keep planting a fresh crop every two weeks.
Dividing Perennials -- You can still divide most perennials as long as they're not spring or early summer bloomers and as long as the foliage isn't more than 5 or 6 inches high. Divide them if they are getting crowded (reduced blooms, a dead spot in the middle) or you simply want more plants.
Deadheading 101 -- Keep deadheading! For the most flowers and tidiest garden, deadhead daily. Some gardeners take a few minutes each morning, making it part of their daily routine. And since roses are going full-tilt, it's especially important to deadhead roses to keep the blooms going longer.
- You can still 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.)
Smart Pruning -- Prune spring-blooming shrubs and trees, such as lilacs, forsythia, and crabapples, as soon as possible after bloom.
- Snap off the old flower heads of rhododendrons, but be careful not to injure new branches emerging right beneath the faded blooms. Also shear azaleas by removing the outermost inch of new growth to encourage foliage developing lower on the stem and an overall bushier plant.
Mulch Matters -- If you haven't already, apply a layer of mulch on flower beds and around trees and shrubs once the soil has warmed sufficiently. As a rule of thumb, this happens about the same time the tulips have faded. Mulch reduces weeds, conserves moisture, and prevents disease. Great stuff!
- Keep new plantings well-watered.
- For mums, pinch off the last inch or so of the branches until July to assure bushy, well-flowering plants. While you're at it, cut back asters and other tall, floppy, late-summer bloomers by about one-third once they're a foot or so high. They'll be sturdier and flower better.
Feeding Roses -- Continue to fertilize roses. In cold regions, Zones 5 and colder, keep fertilizing to a minimum. Studies have shown that keeping your roses a little "hungry" helps them overwinter better. A lean diet prevents too much lush green growth, which can get badly zapped in the winter.
Annual Stakes and Supports -- Stake tall plants that will need it now while they're just a foot or so high.
- Stop cutting asparagus and rhubarb at the end of the month so they can rejuvenate for next year.
- Now is the time to control a number of diseases. Check junipers, birches, cherry and arborvitae for bagworms and other leaf-eating caterpillars, then treat with Bacillus thuringiensis as needed. Watch for fungal disease on tomatoes and roses and spray with a fungicide (a botanical, earth-friendly one if possible). Keep an eye out also for aphids and other small sucking insects. Treat with insecticidal soap.
- Continue slug and snail control.
- Inspect your irrigation system, if you have one, for damaged sprinkler heads, which waste water. Replace as needed.