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Fielding Questions: Dipladenia can be wintered successfully

Q: I purchased two dipladenia plants this spring. How well do they overwinter indoors? - Nicole Welsch, Fargo.

A: Dipladenia, and its close relative mandevilla, can both be wintered successfully indoors and then returned outdoors next spring. We enjoy wintering several each year, and they aren't difficult if given full, direct, bright sunshine in front of a large, sunny window. Before bringing indoors, wash the plants with the garden hose to reduce tag-along insects. Plants can be pruned if they've grown large and repotted now or next spring.

If given enough sunlight, dipladenia will thrive and sometimes bloom indoors. Don't be alarmed if a few leaves turn yellow and drop. Water as you would other houseplants, letting them dry between thorough watering. If leaves are yellowing and dropping, decrease watering frequency. Fertilize with water-soluble fertilizer once a month.

To prevent insect problems, apply granular systemic houseplant insecticide to the soil. In March, prune the plants back, preferably quite severely to encourage good branching, or at least enough to remove weak winter growth. Repot if necessary into fresh soil, and begin fertilizing every two weeks. Move back outdoors in May after frost danger passes.

Q: I have four trough-like planters on a concrete patio. Each is four feet long and one foot wide and tall. Will any perennials or bulbs such as tulips, crocus and daffodils survive the winter in the planters? - Gary Euren, Moorhead.

A: Unfortunately, planters that are above natural ground level are subjected to temperatures too severe for bulbs and perennials to survive. Below natural ground level, soil is more moderately frozen, but planters above ground easily take on the air temperature.

For example, a check of weather records shows that last January in Fargo on a day with air temperature nearly 20 degrees below zero, underground soil temperature was 20 degrees above zero, nearly a 40-degree difference.

If you'd like to try, move the planters to a protected spot along the house foundation and cover with at least several feet of leaves or straw for insulation, and then uncover next spring and move to their desired location. Annual flowers are still the best solution for above-ground planters.

Q: My lawn is top heavy with thick tops, but very shallow roots. My mower is set at three and a half inches, and I was watering daily for 10 to 20 minutes per zone. I think I'm mowing too high and watering too often even though it's been a dry summer. - Jeff Greenheck, Fargo.

A: Your suspicions are probably accurate about watering too often, and the mowing height could be reduced to the preferred three inches. Shallow rooting is usually caused by watering too frequently, which encourages roots to stay near the surface instead of growing downward. The preferred rule of thumb is to apply one inch of water per week in one application, or split between two waterings if soil texture is light. To monitor quantity, locate a straight-sided soup can within the sprinkling zone. Less frequent, but deep watering will keep a lawn green and healthy with a deep, vigorous root system.

If you have a gardening or lawn care question, email Don Kinzler at All questions will be answered, and those with broad appeal may be published, so please include your name, city and state for appropriate advice.