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Want a Second Season from Last Fall’s Mums?

Learn the trick — and the science

Hardy mums planted for color last fall most likely survived the winter and are now rising in clumps in your garden. Here’s how to get them ready to bloom again this fall.
    To move mums to new spots: For lots of smaller plants, dig the clumps and divide them into smaller clumps of one, three or five stems each, with roots firmly attached. Transplant them 12 to 18 inches apart. After they have started to grow, prune the stems, leaving only three or four leaves near the bottom of the stem, for two to three branches per plant.
    To manage them in place: Get out the hedge shears and prune the tops away, leaving only a few leaves at the bottom of the stems. These undisturbed clumps will quickly generate multiple stems. Allow the new stems to grow about six inches before shearing away the upper half of the new growth. Continue shearing away the tops of the plants until July 23. Shear with a slight curve to make them naturally round like a large beach ball. This method will give you bushel-basket sized plants that will flower starting, depending on the variety, in early September until frost.
    Chrysanthemums are short-day plants, meaning that they initiate flower buds when daylight hours are fewer than 10 to 12. Thus you stop shearing them on July 23 so the plants will have time to send up new growth before flower bud initiation begins at the end of each stem. Some varieties require 24 hours of total darkness, while other varieties require only 22 hours of total darkness for flower bud initiation. Exposing the plants to a flash of light from a flood lamp, street lighting or light from vehicles during the daily dark cycle may prevent the plants from flowering. Once the round flower buds become visible at the ends of the stems, total darkness during the dark cycle is no longer necessary.
    Chrysanthemums are similar to poinsettia with regards to short-day requirements. Other common short-day plants are garlic and Vidalia onions. Vidalia onions — planted in Vidalia County, Georgia, in the fall for spring harvesting — require short days to produce bulbs. Just as the Champagne region of France is the unique producer of champagne, Vidalia County is the unique producer of Vidalia onions. The soils in that region are low in sulfur, resulting in mild onions.
    Because of our harsh winters, Maryland is best for long-day (and intermediate) onions. Planted in the spring, these onions produce bulbs because they are growing during long daylight hours.


Pruning Photinia

Q A row of redtip Photinia between my property and my neighbor is over 20 years old and has been pruned repeatedly. They are now taller than the garage but sparse at the bottom. If I cut them down to about five feet, will they fill out? Or are the base branches too thick? I have attended your pruning seminars and I know you can cut back a lot of shrubs and they bounce back. But I want to make sure I won’t do any damage before I proceed.
    I thoroughly enjoy your column and often clip it to keep in my garden notebook.

– Bonnie Smith, Lusby

A Photinia is nearly impossible to kill by pruning, though you should have pruned them before they resumed growth earlier this spring.  When you cold-cut these plants down to the ground, they return like gangbusters.  If you cut them back hard now, they will sprout only at the uppermost branches. If you wait and prune them back early next spring, they will grow new sprouts at the bottom.

Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.