University of Vermont Extension 
Department of Plant and Soil Science

Spring Article

DIVIDING PERENNIALS AND OTHER MAY GARDENING TIPS

Charlie Nardozzi, Chairman of the Board of Directors
Vermont Botanical Garden, and
Dr. Leonard Perry, Extension Professor
University of Vermont
 

Dividing perennials, planting cole crops, and supporting tall perennials are some of the activities for this busy month in the garden.

Now is a good time to dig and divide later blooming perennials if needed, such as hosta, ornamental grasses, perennial geraniums, bee balm, daylilies, helen's flower, and asters. If left undivided, plants may become unproductive and overcrowded, often bare in the centers. Wait until after bloom to divide overgrown early-blooming perennials such as yarrow and evening primrose.  Even though peonies bloom in early summer, wait until fall to divide them if needed.

Dig up the clump, and with a sharp spade create wedges. I usually like to divide the clump in half, then divide each half further.  Leave large divisions if you want plants to look better, and bloom more, sooner. After replanting, water often and deeply to reduce stress on these new divisions.

It's time to start planting cole crops such as broccoli, cabbage, and cauliflower. These crops should be planted about 2 weeks before your last frost date, on raised beds in soil amended with compost. Don't be concerned if the leaves turn red or purple. It's often a sign of phosphorus deficiency due to cool soils and will go away once the soil warms.

As your asparagus shoots start emerging, harvest spears at least pencil width from asparagus plants that are at least three years old. Cut the spears at ground level with a sharp knife and eat them that day for the best flavor.

Check apple, cherry, and other fruit trees for nests of tent caterpillars. They will emerge at the same time as leaves sprout. Blast low-lying nests with water to destroy them or spray Bt (biological pesticide) on emerging caterpillars. This will harm only the caterpillars and not other beneficial insects, birds or humans.

Support plants that tend to flop over now, while they're still small. Use wire cages to support peonies, perennial sunflower, and New England asters for example.  If you set the cages in place now, the foliage will soon hide them. In contrast, trying to tie up toppled plants is frustrating and usually ends up looking unsightly.

Don't remove foliage from fading spring-flowering bulbs like daffodils and tulips until it dies back on its own. The plant needs the foliage to manufacture and store food in the bulb in preparation for next year's bloom. Removing green foliage weakens the plant. Wait until the foliage yellows on its own in midsummer before trimming it back. In the meantime, hide the unsightly foliage by doubling it over and tying with rubber bands.

Consider interplanting spring bulbs with annual flowers to help hide this foliage as it dies back.  Keep in mind that unless your tulip varieties are "perennial", most behave as annuals and only bloom well the first year.  If this is the case, you can remove them after bloom.  If you just have just a few perennial spring bulbs, or some special ones, you may want to water them with some liquid fertilizer during or after bloom.  This too will help them have better bulbs and blooms for next year.

If you have rabbits nearby, try poultry wire fencing around vegetable gardens and flower beds to prevent their foraging.  Make sure it is a foot or more above ground, and six inches or more below ground to deter their digging.  You may also use pepper sprays on seedlings, just make sure all parts of the plant are covered. Reapply after rains.

Other tips for this month include not forgetting mothers on their day with a special container or hanging basket of flowers.  Fertilize lawns according to soil test recommendations (available from universities and Extension services).  Keep lawns mown regularly, increasing the mowing height as the season progresses.  If planting crabapples, make sure and choose disease-resistant selections.


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