University of Vermont Extension 
Department of Plant and Soil Science

Spring News Article

HARDENING SEEDLINGS AND OTHER MAY GARDENING TIPS

Charlie Nardozzi, Senior Horticulturist
National Gardening Association, and
Dr. Leonard Perry, Extension Professor
University of Vermont
 

Hardening seedlings gradually to outdoor cold before planting outside, pruning woody perennials and roses, and using less soil in large containers are some of the gardening tips for this month.

When planting large containers for the deck or patio, save on soil by creating a false bottom.  Put some foam packing peanuts in the very bottom, then cover with landscape fabric or a piece of cardboard to keep the soil from sifting around the peanuts. Or you can use plastic pots, upside down, instead.  Most of the plants you'll use don't need more than about a foot of soil depth for their roots.

Woody perennials differ in the way they should be cut back in spring. If butterfly bush has died to the ground, cut the dead stems to the ground. Otherwise, just shorten them by about one third. Cut back Russian sage, rue, and artemisias to about 8 to 12 inches from the ground. Don't prune lavender until new growth appears, and then just shorten the stems by about one-third. Heather should be lightly pruned to remove the old flowers and the tips of the shoots, but don't cut back to brown wood, stay in the green.

Check apple, cherry, and other fruit trees for nests of tent caterpillars. They will emerge at the same time the leaves sprout. Blast nests with a strong spray of water to destroy them or spray “Bt” insecticide on them. Bt will harm only the caterpillars and not other beneficial insects, birds, or humans. You'll need a pump sprayer for this job.

Cut back dead canes of roses to healthy tissue, and remove any spindly branches. Make a slanted cut that angles up toward an outward-facing bud, starting one quarter inch above the bud. This directs the new canes to grow outward, which improves air circulation in the middle of the plant and so reduces the risk of diseases like black spot.

Be sure to harden off indoor-grown seedlings before setting them into the garden. Skipping or rushing this process can result in chill damage to tender growth. Acclimate plants to outdoor conditions over the course of at least a week, and preferably two, by gradually increasing the amount of time you leave them outdoors.

Now is a good time to dig and divide perennials if needed, before new shoots grow over a few inches high.  Fewer blooms last year, leggy stems, and open centers of plants are signs they may need dividing.

Other gardening tips for this month include transplanting cool-loving crops such as cabbage, kale, and snapdragons out early, protecting bees by not using insecticides on plants in bloom, and keeping up with mowing so you don’t mow too much off at any one time.  Visit the National Gardening Association’s web site (www.garden.org) for more information on gardening and regional reports.


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