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WICHE: Age, fertility two factors for bloom

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By Jeneen Wiche

I have no complaints about plant performance this spring.

It has been England-like with agreeable temperatures and ample rainfall, thus far.  A few steamy days have managed to snap me back to summer-in-the-Ohio valley-reality!

Plants have preformed well and bloomed as they should here at the farm, but some gardeners continue to pose the question, “Where’s the bloom?”

Why plants fail to bloom is a difficult question to answer because a great many things factor into poor performance, lack of bloom or die back.  Looking to the past can reveal some clues, however.

Do not forget that we had a drought last summer.  Drought stress, desiccation from wind and ice load may mean death or die back for some plants, lack of vigor or bloom for others.

Additional factors to consider include age, pollination, planting depth, mulching, improper pruning, over fertilization, environmental stress, insect or disease problems and exposure to sunlight, darkness, adequate winter chilling, and whether a plant is seedling grown or grafted.

I will bet you didn’t realize the list was so long.

Many trees need to reach a level of maturity before they will bloom.  Usually after seven years trees, are ready, although seedlings may take a little longer than grafted trees.  Additionally, drought-susceptible trees such as dogwoods and sweet bay magnolias, for example, may bloom poorly after a season of drought. 

Lack of flower and fruit for pears and apples, and their ornamental cousins, can be blamed on two different things.  Fruiting trees need 300-600 hours, depending on the species, of temperatures below about 40 degrees.  If they do not have enough chilling time they bloom poorly.

I think we adequately reached the goal last winter. Fruit trees also have a tendency to bloom and fruit every other year, resting the alternate years. Additionally, cool spring weather can reduce insect activity, which than reduces the amount of cross-pollination that is taking place.

Pruning woody plants at the wrong time also can eliminate wanted blooms. Spring flowering shrubs set buds during the early part of the summer, so if you prune them after mid to late June you will be removing next year’s bloom.

Prune spring flowering shrubs like lilacs, azaleas and rhododendrons right after they finish blooming.  

Hydrangeas, for example, have different blooming habits.  The oakleaf and “Annabelle” hydrangeas can bloom on new growth, but H. macrophylla blooms on last year’s growth. So prune accordingly.

The same goes for blackberries. Prune out old wood at the end of the season after fruit has been harvested. Save the current season’s new growth for next year’s harvest.

Remember that patience is a virtue; you must allow the foliage of spring flowering bulbs to yellow out naturally before you cut them back.

The foliage continues to photosynthesize, storing up energy for next year’s bloom.  If you remove the foliage prematurely, not enough energy is stored for the following year’s display.  Mid-to-late June is usually the target date for removing the foliage of spring flowering bulbs.

Insects can diminish blooms as well. Thrips and aphids can suck the juices from a bud, rendering it useless in the bloom category. Caterpillars and beetles just eat the bloom (and some come out only at night leaving us with no one in plain sight to blame).

If you have a lawn-care company that treats your turf with herbicides, chemical drift can burn foliage, bud and bloom.

Over-fertilization, especially too much nitrogen, can also wreak havoc on the bloom cycle of plants.  Nitrogen encourages foliar growth at the expense of bloom, so avoid over fertilization.

Don’t always assume the worst when your plants fail to bloom. Give them some thought, and you will likely figure out the problem, so you can make the appropriate adjustments.