This is a favorite shrub with many gardeners because of their vine-like shoots and their eye-catching blossoms. Most hydrangeas originate from Asia and North America. Hydrangea macrophyllia are the big leaved and common along the Atlantic border states. They have big, beautiful blossoms of blue, lavender and white. More common is the hydrangea paniculata or panicle hydrangea. Then there’s the climbing hydrangea or Hydrangea anomola-petiolaris which is often seen on the northern sides of buildings and homes.
Hydrangeas blend nicely with rhododendrons, azaleas and the forsythia. When you plant them near each other you can almost bet you’ll always have something in bloom. Depending on the variety they’ll bloom from summer to autumn.
Your blossom color is relevant to the Ph level in your soil. Acidic soil will bring you blue to violet flowers, while neutral to slightly alkaline will give you pink to white. They can range in sizes from 5-10 inches in diameter.
Hydrangeas prefer light to medium shade although the big leaved can handle full sun provided they’re given enough water. They like moist soil but will do well in most soil conditions. They do better with at least 1.5 inches a week and 2 during the heat of the summer. Ease up on water early September to October as not to encourage fall growth. Give them one last good soaking before it freezes to supply shallow roots some moisture before winters dryness.
Hydrangeas really only require one feeding of fertilizer in the spring. A good compost or rich manure is really all that’s necessary but they’ll benefit from monthly feedings for up to three months. I’d go May to July in the south and June to August in the north. Liquid seaweed extract is best or any organic fertilizer will do. If you choose chemical fertilizer use a slow release. If you’re not sure how much to use it’s safer to use too little than too much. Pour around the drip line of the shrub; not near the base.
Pruning always brings best results after flowering has occurred. Big leaved hydrangeas get their flowers from buds of the previous growing season. Prune about a third of the weakest growth early in the spring. This will ensure new growth and encourage flowering.
Of course with flowers as big and brilliant as the hydrangea, pests will be attracted to them.
Some of the most common pests can be controlled without much cost and effort, really. Aphids suck the sap from the leaves which causes them to turn yellow. and sometimes brown. In bright sunlight the leaves will wilt or curl; this will cause a stunt in the growth. Aphids have pear-shaped bodies and are about the size of a tip of a pencil. They will be on the under side of the leaves. You can spray them away with a fine mist from your garden hose.
If you notice leaves turning brown and some seemingly threaded together and curling; this may be from leaftiers. The leaftier larvae tie leaves together for protection while they are feeding. You may notice 1/2 inch green caterpillars with brown heads. Remove them and drop them in a bucket of soapy water. Crush the larvae in the curled leaves and spray the leaves every couple of days until they are all gone.
If you see leaves turning brown on their edges or leaves looking burned, this is probably from spider mites. These mites are tiny and too small to see with an unassisted eye. You might have better luck with a magnifying glass. You can spray leaves down every day for three or four days. Try to do this in the morning to not promote sun scalding. For heavier infestations use a light solution of insecticidal soap.
Hydrangeas are prone to stem nematodes and root nematodes. Stem nematodes will make the stems swollen and split. The leaves will soon fall off. The shrub will become wilted and stunted with yellowish bronzed leaves when root nematodes are at work. Nematodes are round worms. Most are in the soil and very tiny. Fertilize with fish emulsion and lots of compost to encourage beneficial fungi. This will turn the nematodes away.
Diseases and pest infestations sometimes are difficult to distinguish. I encourage the use of a magnifying glass to help identify problems.
Blight is a common fungus disease that causes spots to develop into larger blotches. This is most common in wet seasons. Spray with fungicide once a week and prune smaller shoots to encourage air circulation. Avoid over watering.
If you notice a thin, white layer on the underside of leaves this is powder mildew. As soon as you notice this, spray the leaves with a sulfur based fungicide once or twice a week, depending on the severity.
Rust fungi will cause leaves to turn spotty brown and yellow and become brittle. Prune the infected leaves and spray with a wettable sulfur based fungicide once a week until it's all gone.
If you would like to see some stunning photos you will want to visit Judith King at Hydrangeas.