For a moment in midsummer, it seems that hydrangea blossoms will roll in forever like ocean waves, but as Shakespeare reminds gardeners, "summer's lease hath all too short a date." You'll want to prepare your hydrangea bushes (Hydrangea spp.) for a long winter's dormancy in late fall, and the rougher the winter in your area, the more work will be required.
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Zoning Out Your Perennial Garden
Don't wait until leaves fall to think about helping hydrangeas make it through the winter. Before you plant, select shrubs that match your plant hardiness zone. You'll find hydrangeas that thrive in U.S. Department of Agriculture plant hardiness zones 3 through 9. For example, a bigleaf cultivar called "Endless Summer" (Hydrangea macrophylla "Bailmer") grows well in zones 4 through 9, while oakleaf hydrangea (Hydrangea quercifolia) prefers zones 5 through 9. Matching your plants to your climate is the single best method of making sure they survive the winter. Plant it in well-drained, organically rich soil in a part-sun/part-shade location that is protected from winter winds.
To Prune or Not to Prune
When to prune hydrangeas can be confusing. Some hydrangeas -- like the bigleaf (Hydrangea microphylla, zones 6 through 9) flower on old wood. To preserve buds, prune immediately after the flowers fade, usually midsummer. If you prune these plants to the ground in autumn, you'll have no flowers the following spring.
Shrubs that flower on new growth -- like panicle hydrangea (Hydrangea paniculata, zones 4 through 8) can be pruned back just before or during winter. You'll get bigger blossoms by cutting all stems off at the ground, but the new stems that grow in spring may be floppy. To prevent this, prune to 18 or 24 inches. Always wipe the pruner's blade with a rag soaked in denatured alcohol to be sure you don't spread disease. Whether or not you prune, clean up dead leaves and trim off diseased or broken branches in autumn.
Water and Food for Winter
Water yes, fertilizer no is the general rule for preparing hydrangeas for winter. Give the shrubs a deep drink before the ground freezes, and they will dehydrate less, according to experts at the Fine Gardening website. But no need to fertilize these shrubs before they go into dormancy. Instead, feed the soil by laying 2 to 3 inches of organic compost or shredded leaves over their root area as mulch in late fall. Mulch adds an extra layer of protection to keep the ground warmer in the cold and cooler in the heat. It then disintegrates into the soil, enriching it. Be sure to keep the mulch a few inches away from the plant foliage. Reliable snowfall acts as a mulch in cold regions.
Covering Up Hydrangeas
If you're trying to grow hydrangeas below their preferred zones, you'll need to offer extra cover-up protection. For smaller plants, upend a cloche or empty flower pot over the shrub and top it with a brick to weigh it down. Wrapping a shrub in burlap offers even greater cold and wind protection. If you are worried about heavy snowfall, plant a few tomato stakes into the ground as a skeleton for the burlap. Make the burlap walls at least 6 inches taller than the shrub. Be sure to remove these coverlets when spring arrives.