Extension News

Ask the ISU Extension Garden Experts: Cold Weather Impacts and Care of Miniature Roses

Note to media editors: Got gardening questions? Call the Hortline at (515) 294-3108, Monday-Friday from 10 a.m. to noon and 1 to 4:30 p.m., or e-mail us at hortline@iastate.edu. For more gardening information, visit us at Yard and Garden Online, http://www.yardandgarden.extension.iastate.edu.

2/10/2009

Our area experienced temperatures in the -20 to -25 degree range in January. What effects will the cold temperatures have on my trees and shrubs?

Trees and shrubs that are native to Iowa (or similar regions of the world) are well adapted to our climate and should have suffered little or no damage. Flowering dogwood, Japanese maple, and other plants that are marginally hardy in our state may have sustained damage. The cold temperatures in January may also have destroyed the flower buds on several spring-flowering shrubs.
The maximum cold hardiness of most flowering dogwood and Japanese maple varieties is -20 degrees Fahrenheit. Flowering dogwoods and Japanese maples in the state may have sustained damage. Damage may vary from the dieback of twigs and branches to complete death of the tree.
The cold January temperatures may also drastically reduce this spring’s floral display on forsythia and flowering quince. Temperatures of -20 degrees Fahrenheit or below likely destroyed the flower buds on flowering quince and several forsythia varieties, such as ‘Spring Glory’ and ‘Lynwood Gold.’ Flowering this spring may be limited to those areas below the snow line. Fortunately, the cold temperatures should not have any long term effects on the shrubs. The leaf buds on forsythias and flowering quince are hardier than their flower buds. The shrubs should leaf out normally in spring.

I received a miniature rose for Valentine’s Day. How do I care for it?

Miniature roses need direct sun. In the home, place the miniature rose in a south or west facing window. Rotate plants once or twice a week to promote even growth.

Miniature roses also require a consistent moisture supply. When the soil surface becomes dry to the touch, thoroughly water the plant until water flows freely out of the bottom of the container. Discard the excess water. Fertilize the miniature rose (once or twice a month) with a dilute fertilizer solution.

Miniature roses prefer daytime temperatures around 70 degrees Fahrenheit and a minimum nighttime temperature of 60 degrees Fahrenheit. Keep the plant away from cold drafts or heat sources.

To promote new growth and additional blooms, remove flowers as they fade. Cut off the stem just above the uppermost five-leaflet leaf. Also, remove any yellow leaves or dead growth.

Finally, periodically inspect the miniature rose for pests. Roses often have problems with spider mites when grown indoors. Discolored leaves and fine webbing are indications that spider mites may be present. Control spider mites by spraying plants with insecticidal soap. Several applications may be necessary to completely control the spider mites.

In May, the miniature rose can be placed outside. Acclimate the plant to outdoor conditions by initially placing the plant in a shady location. Then gradually expose it to longer periods of sunlight. After the miniature rose has been acclimated outdoors for several days, place the potted plant on a sunny patio or deck. The miniature rose can also be planted outdoors in the garden. While miniature roses are small, they’re actually more cold hardy than hybrid tea roses. Select a sunny site with fertile, well-drained soil.

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Contacts :
Richard Jauron, Horticulture, (515) 294-1871, rjauron@iastate.edu 

Del Marks, Extension Communications, (515) 294-9807, delmarks@iastate.edu