MASTER GARDENER PROGRAM — MGs in the News
Published in The Oregonian Homes & Gardens of the Northwest staff • May 18, 2016 at 7:08 AM
Molly Moore is a Master Gardener in Clark County, a program run by Washington State University Extension. She says the reason a plant fails to bloom could be because of the temperature, light, fertilization, pruning or its maturity.
Plant maturity: Many woody shrubs can take years to bloom. During its juvenile stage, a plant’s energy is focused on vegetative growth (roots, stems and leaves) before starting reproductive processes such as flowering and fruiting. Some shrubs can take 2 to 3 years to reach maturity, and trees can take 5 to 10 years.
Rootstock type (for grafted trees or shrubs) can affect the age of maturity. For example, dwarf apple and pear trees can start blooming after one or two years, while standard size apple and pear trees can take up to seven years to reach maturity.
Temperature: Low winter temperatures can destroy tender flower buds. This may be seen in Forsythia after a particularly cold winter. A cold-injured shrub may have blooms on only the parts of the plant that were protected by snow.
If you suspect cold-injury in a flower bud, cut it in half lengthwise. If there is browning on the interior, the blossom may be damaged and the shrub may not blossom this year.
Light: Most flowering shrubs need at least some light to flower. Check plant tags to be sure you are siting a plant in a place where it will get the necessary amount of light. Lilacs will not bloom if they are in too much shade.
Fertilization: Too much nitrogen can lead to lush green foliage, but can prevent a plant from blooming. If you fertilize and notice a decrease in flowering, stop or reduce fertilizing and your plant may recover. It may take up to two years to begin flowering again.
Pruning: Over pruning and insufficient pruning can result in lack of flower bloom. Older or improperly pruned shrubs can become woody with little new growth and they may become very dense, blocking sunlight from reaching flower buds.
Pruning at the right time of year is essential to ensuring flowering. Pruning a spring blooming plant such as flowering current or Japanese andromeda too late will remove the flower buds they’ve set for next year’s flowers. These plants should be pruned shortly after they are done flowering.
Summer blooming shrubs such as hibiscus set their flowers shortly before blooming, so these can be pruned in early spring before growth starts.
If you have questions about your flowering shrubs or other landscape or edible plants, contact the WSU Extension Clark County Master Gardener answer clinic at mganswerclinic@clark.wa.gov or 360-397-6060 x 5711. Emails should include the specific plant problems and two or three high-quality photos depicting both the affected area along with some of the healthy areas of the plant.
Or stop by the extension office to talk to a master gardener volunteers from 10 a.m. to 2 p.m. Tuesday or Wednesday or 11:30 a.m. to 3 p.m. Thursday and Friday at 1919 NE 78th St., Vancouver.
— Molly Moore
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