Hydrangea is indigenous to Asia and both American continents with over 75 species in the genus. East Asia, specifically Japan, China, and Korea have the greatest diversity in species. Most species are shrubs 3 to 10 m tall, while others are small trees or lianas that climb up trees to almost 100 feet long. While the popularly grown species are all deciduous, there are some evergreen varieties.
The name “hydrangea” comes from the Greek word “hydor” or water and “angeion” or vessel, denoting the seed pods of the plant that resemble small water jugs. The species was first given the Latin name “Hortensia” after the 18th-century French mathematician and astronomer Nicole Hortense Lepaute.
The plants usually bloom from spring to autumn, with the flowers often growing in clusters at the tips of the stems. Typically, these clusters or flower-heads have two types of flowers – small inconspicuous flowers at the center of the cluster and big, showy flowers with colorful sepals. The showy flowers quite often surround the small flowers in a ring. While wild plants generally have very few or no showy flowers, cultivated hydrangeas have been selected and bred to produce the larger type of flowers.
Generally, most species produce white-colored flowers, but the colors of flowers in some specific species can range from red, pink, blue, light, or dark purple – the varied colors are due to the acidic or alkaline pH levels of the soil.
Soils with pH below 7 or acidic typically make some varieties put out flowers that are purple to blue, while soils with pH above 7 or alkaline soil will result in red or pink flowers. This capability is also subject to the cultivar as some are selected and bred to be blue, while others are selected and bred to be pink, red, or white.
To produce blue flowers, pH levels are lowered by adding peat moss or sulfur to the soil, while soil pH can be elevated by the addition of ground limestone to produce pink/red flowers. Generally, not all hydrangea species can adjust their flower colors.
While most hydrangea species are deemed to be toxic.
Overall, hydrangeas prefer to grow in partial shade, with full exposure to the sun in the mornings, with some shade to shield them from the hot sun at midday. Some varieties can tolerate full sun.
Hydrangeas prefer plenty of consistent watering, thrice-weekly at least during their growing season this helps encourage root growth.
Leaves will begin wilting and flowering will be hindered with under-watering.
It’s best to water hydrangeas in the mornings to help prepare them for the hot day and to prevent disease. Organic mulch will help the soil stay moist, adding nutrients as it slowly decays to help improve the soil.
Avoid getting water on the foliage or flowers.
Hydrangeas can tolerate average or high humidity levels, dry air in winter can cause damage and leaf wilt, so keep a humidifier nearby. Avoid drafts and heat sources.
Preferably, daytime temperatures ought to be around 70°F and just below 60°F at night. The temperature has to be kept below 65°F for around 6 weeks to promote the formation of flower buds. After this time, the plants should go dormant under temperatures between 35-45°F for about six weeks.
Most varieties of hydrangeas thrive in organic and well-drained soils that get plenty of water. Amend poor soil by adding compost to improve quality. Although hydrangeas prefer moist soil, they won’t tolerate being waterlogged as poor drainage causes root rot and kills the plant within a few weeks.
Repot hydrangeas in spring or summer when root growth is active. Select a pot with ample drainage holes, about 1-2 inches wider than the current one. Fill the pot with appropriate soil, dig a hole that is as deep and wide as the root ball, insert the plant fill in the space with soil, and water it. When the soil has settled down, top up the remaining spaces with soil and thoroughly water it again.
Hydrangeas are easily propagated from cuttings. Find a branch of new growth on a healthy hydrangea that hasn’t flowered yet. New growth appears lighter in color and not as rigid as older growth. Take a 5-inch cutting that has at least 3-4 pairs of leaves on it, remove the last pair of leaves – you can remove more leaves if necessary, but retain at least 4 leaves at the top of the cutting.
Take a small pot filled with dampened soil mix, insert the cutting into the soil until the remaining leaves are near the top of the soil and lightly water it. Then it should be protected from direct sun and drafts in a warm location.
Check the cutting regularly to ensure that it’s not rotting and water only when the topsoil is dry. Roots should be set within a few weeks.
If the soil is rich in organic material, you might not have to fertilize your hydrangea. The best option to determine this is to test the soil, too much fertilizer promotes leafy growth and fewer flowers.
Each hydrangea variety has different fertilizer needs and benefits from different times of application, plants with pinkish flowers need fertilizers with more phosphorus and nitrogen and less potassium, while plants with blue flowers need fertilizers that are richer in potassium and less phosphorus and nitrogen.
Some plants should be pruned annually when new leaf buds appear. If they are not pruned regularly, the plant will become very gangly, growing taller until the stems cannot handle the weight, sagging down and possibly breaking. Other varieties produce flowers on older growth and new growth from pruning will not develop flowers until the next season.
Outdoor plants should be pruned before spring, removing leaves and branches around the plant’s base. In warm climates, pruning is usually done after flowering to enhance the production of lateral buds for the next season. Indoor plants must be pruned in September, leaving 2 buds on each branch.
If the plant becomes old or is neglected or damaged, cut all the stems right down to a few inches above the soil. It will not produce flowers for the next season, but this will rejuvenate and revive the plant for the future.
Pests and disease can be avoided first of all by selecting cultivars bred with resistant traits. Common issues like leaf spot, wilt, and powdery mildew can affect these plants. Pests such as spider mites, aphids, and leaf tiers usually don’t affect these plants, but do appear if the plants get stressed.
Fungi and nematodes that cause shortened or twisted or wide stems can also plague the plants. Treating these is not that effective, so preventive measures are the preferred method – sterilize the soil and remove infected plants.
Overall, proper care and maintenance is the best defense.