By C. Rae Hozer
When we observe plants in natural settings, in farm fields and pastures or in home landscapes, seasonal changes are evident. Spring and fall are universally recognized as transition times — spring leading into summer and autumn to winter. Yet, less visible plant processes take place in winter and summer, making them times of botanical transition as well. Understanding plant behind-the-scenes biological processes helps gardeners get the timing right when we fertilize, prune, transplant, sow seeds or use weed treatments during the last six months of the year.
Trees and shrubs need a long time to get ready for the next winter and spring. They must store energy and develop buds for the coming season’s shoots and blooms. Perennials and biennials (plants that live more than one year outdoors) are already storing carbohydrates by July 1, under normal conditions. Woody-stemmed plants must be able to persist in the open air during winter unlike herbaceous perennials whose top-growth (in most cases) dies back to the root system during the cold season and then grows anew the following spring.
Water swells when it freezes. New growth is vulnerable to freeze damage because it is full of moisture which expands and may destroy cell walls, if frozen. Trees and shrubs adopt defenses against cold air temperatures and drying winter winds through hardening measures. This results in less moisture in above-ground structures and also formation of protective plant parts like bud scales.
Both pruning and applying fertilizers with a high proportion of nitrogen stimulate shoot and leaf growth. Nitrogen applied in mid-August or September stimulates growth that will probably have too little time to harden. Damage from freezing can lead to rot and provide a spot for disease entry which can threaten the plant’s survival. Fertilize perennials before the end of July or wait until 2014. Late-season growth just below cuts is one reason to avoid pruning in August, September and October. A second problem is that spring-blooming woody plants and other woodies said to “bloom on old wood” set flower buds (for next season) starting in July of this year. Removing branches now also cuts back the number of blossoms you see the following year.
Rain in May and June encouraged tall flowering plants in my yard to grow leggy. Heavy down pours during Tennessee’s 2013 "monsoon season" knocked many of them over. What were supposed to be close-growing, cottage-style gardens and a butterfly wildflower meadow looked a jumbled mess. Now is a good time to use a combination of staking and cutting plants back to encourage re-bloom and return similar areas on your property to some type of order.
In the Neighborhood—Hydrangeas
I have been admiring hydrangea blooms in my neighborhood, though I don’t grow a single one myself. The reason for that goes back to the number one mandate for landscapes — “Put the right plant in the right place.”
Planting hydrangeas in the right place is very important. Most hydrangeas grow well and present a satisfying floral display in a location with morning sun and afternoon shade. PeeGee hydrangeas (Hydrangea paniculata ‘Grandiflora’) tolerate more sun and heat than the commonly grown big-leaf hydrangeas (Hydrangea macrophylla species). Oakleaf hydrangea (H. quercifolia) a U.S. native plant, tolerates more shade, but no hydrangea does well in heavy shade under trees, which is what I have.
Get lots of good hydrangea information online at www.usda.gov/Gardens/faqs/hydrangeafaq2.html.
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Plateau Gardening is written by Master Gardeners for gardeners in Tennessee’s Upper Cumberland Region. Contact UT Extension Cumberland County at P.O. Box 483, Crossville, TN 38557 (484-6743) for answers to horticulture questions, free publications and how to become a Master Gardener. Send email comments or yard and garden inquiries to Master Gardener Rae, MGardenerRae@frontiernet.net.