Learn About Hydrangeas
How to Sow
Hydrangea is planted as a potted plant.
Planting Potted Plants in the Garden:
- Hydrangeas may be planted in partial shade or in full sun. In the south shade is better for them. In the north full sun is better. Some varieties are more tolerant of sun than others. Select a location with soil rich in organic matter. Avoid planting too close to trees which will compete with them for moisture.
- Prepare the bed by turning the soil under to a depth of 6-12, inches removing any debris, and lightly raking as level as possible.
- The addition of organic matter (leaf mold, compost, well-rotted manure) benefits all gardens and is essential in recently constructed neighborhoods.
- Plant on a cloudy day or in late afternoon to reduce transplant shock.
- Dig a hole for each plant large enough to amply accommodate the root ball.
- Unpot the plant and gently loosen the root ball with your hands to encourage good root growth.
- Place the top of the root ball even with the level of the surrounding soil. Fill with soil to the top of the root ball. Press soil down firmly with your hand.
- Use the plant tag as a location marker.
- Thoroughly water and apply a light mulch layer on top of the soil (1-2 inches) to conserve water
How to Grow
- Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their germination.
- Mulches also help retain soil moisture and maintain even soil temperatures. For perennials, an organic mulch of aged bark or shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.
- Careful watering is essential in getting perennials off to a good start. Water thoroughly at least once a week to help new roots grow down deeply. Soil should be damp at about 1 inch below the soil surface. You can check this by sticking your finger in the soil. Water early in the morning to give all leaves enough time to dry. One inch of rain or watering per week is recommended for most perennial plants. You can check to see if you need to add water by using a rain gauge.
- After new growth appears, a light fertilizer may be applied. Keep granular fertilizers away from the plant crown and foliage to avoid burn injury. Use low rates of a slow release fertilizer, as higher rates may encourage root rots.
- “Deadhead”, remove spent flower heads just below the inflorescence (the cluster of flowers) to encourage continuous flowering and prevent seed development. The flowers of some varieties dry nicely on the plant.
- In colder regions, apply another layer of mulch (1-2 inches) after the ground freezes in fall. Evergreen boughs (from Christmas trees) provide additional protection. Remove this mulch in the spring.
Hydrangeas make beautiful cut flowers and add a nice touch to borders. Many varieties are also great for containers.
Pruning is very important and will vary depending on the species of the plant:
Hydrangea quercifolia (Oak Leaf Hydrangea) bloom on last year’s wood, only prune any pruning that needs to be done is just to control height. Prune right after it is finished blooming or just remove the dead flowers.
Hydrangea macrophylla (Big Leaf Hydrangea): This species blooms on last year’s wood. Any pruning that needs to be done is just to control height. Prune right after it is finished blooming or just remove the dead flowers.
Hydrangea serrata ( Mountain Hydrangea): This blooms on last year’s wood. Prune right after it has finished blooming or just remove the dead flowers.
Hydrangea paniculata (Peegee Hydrangea): This blooms on this year’s wood. Prune in early spring before new growth starts. For the largest flowers, thin to 5-10 primary shoots. Note that the weight of the flowers can cause the branches to arch downward.
Hydrangea arborescens (Hills of Snow Hydrangea): This blooms on this year’s wood. Prune in early spring before new growth starts. Hills of Snow hydrangea may be left unpruned (except for removing dead branches). In this case it will produce many smaller clusters of flowers.
Common Pests and Problems
Common Disease or Cultural Problems
Botrytis: This fungus causes a grey mold on flowers, leaves, stems and buds. It thrives in cool wet weather conditions. Burpee Recommends: Remove affected plant parts, avoid watering at night and getting water on the plant when watering. Make sure plants have good air circulation. Contact your Cooperative Extension Service for fungicide recommendations.
Cercospora Leaf Blight: Small flecks which develop a yellowish halo appear on the leaves and turn brown and coalesce. They cause the leaves to wither and die. Burpee Recommends: When watering avoid wetting the leaves. Contact your Cooperative Extension Service for fungicide recommendations.
Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.
Rust: A number of fungus diseases that cause rust colored spots on foliage and stalks. Burpee Recommends: For serious infections contact your Cooperative Extension Service for fungicide recommendations.
Virus (Various causes): The most characteristic sign of virus is tight and dark green mottling of the leaves. Young leaves may be bunched. Young plants may have a yellowish tone and become stunted. Burpee Recommends: This disease is readily spread by handling. Destroy diseased plants and the plants on either side.
Common Pest Problems
Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps which feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Lygus Bugs (Tarnished Plant Bug): Lygus bugs are ¼ inch long and are green or brown with yellow markings. Nymphs are flightless and smaller than the adults. They suck on stem tips and flower buds and inject a toxic that deforms roots, stems and ruins flowers. Burpee Recommends: Because lygus bugs over winter in garden debris, remove all debris after the first frost. Contact your Cooperative Extension Service for insecticide recommendations.
Scale: Small bugs look like brown, black, gray to white bumps on the stems of plants. Scale may not have any apparent legs and may not move. Scales have a sucking mouth part. Scale may produce honeydew so leaves and stems may be sticky. Scale can weaken the plant causing it to grow very slowly and may wilt at the middle of the day. Burpee Recommends: Completely spray the stems with Insecticidal soap. For a severe infestation contact your local County Extension Service for recommendation for your area.
Spider Mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recommends: Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for miticide recommendations.
Whitefly: These are small white flying insects that often rise up in a cloud when plants are disturbed or brushed against. Burpee Recommends: They are difficult to control without chemicals. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for pesticide recommendations.
Does hydrangea make good cut flowers? Yes, but they do need some special care. Make a fresh cut. Plunge the end into very hot or boiling water for 30 seconds to seal the end before using it in an arrangement. Many hydrangea flowers are lovely dried as well.
How do I change the flower color of my hydrangea? You can only change the color of pink and blue-flowering macrophylla hydrangeas. Blue needs an acid soil (low pH) and pink needs an alkaline soil (high pH). Soil acidifiers lower pH and lime raises pH. Never change your soil pH by more than a half a point per year.
Why isn’t my hydrangea blooming? Several factors will affect hydrangea blooming. Young plants may only produce a few blooms in their first couple of years. If improperly pruned or pruned at the wrong time, flowering buds can be accidentally removed, and without flowering buds, there will be no flowers. If the winter was severe, varieties that bloom on old wood may have had their flower buds killed. Too much nitrogen in the soil, possibly from a fertilized lawn, will encourage green growth at the expense of flowers.
Why are my hydrangea flowers turning green? This is usually due to the high heat. As the flowers age they will develop some of their color back again. New flowers that are produced when it is cooler will have normal colors.
Can I grow hydrangeas in containers? Many smaller varieties are ideal for container growing. Use a commercial potting mix rather than garden soil, and regarding hardiness, consider yourself one hardiness zone colder when you choose a variety. Plants in containers are not as well protected in winter as plants in the ground.