When And How to prune hydrangeas
The first step of When And How to prune hydrangeas is to identify the variety, as this determines how, when, and even if it needs pruning. There are 2 main groups of hydrangeas:
Flower colour generally depends on the type of soil and whether it’s alkaline, with a pH above 7, or acid, with a pH below 6. For blue flowers, the ideal is below 5,5. By changing the pH of the soil you can manipulate the colour of the flowers and ensure blues remain blue. However, most of the new intense red hydrangeas are colour fast, keeping their colour, whether grown in a soil with a low or high pH. Whites can be tinged with pink or blue depending on the pH.
Pink hydrangeas are usually an indication that the soil is alkaline with a high pH, and as they can’t take up any aluminium from the soil, they remain a pink colour. Enhance the pink by raising the pH with a handful of agricultural lime sprinkled around the roots of each mature plant in spring and watering it in.
- Incorporate acid compost at planting time, use acid mulch like oak leaves, peat, pine needles and bark.
- Apply a foliar spray of aluminium sulphate, flowers of sulphur or a commercial blueing agent or water one of these in twice a month from early August through the growing season.
- Use a mixture of 25g aluminium sulphate to 1 litre of water and water in well. Avoid excess use on very young plants; plants in containers will need lower doses.
- Don’t grow blue hydrangeas near walls as the lime leached from the cement in the foundations is alkaline.
- Where the water and soil are alkaline, it’s easier to maintain the blue shades if plants are grown in containers.
- Check the pH of your tap water as this can affect the colour of your flowers too.
For signs of chlorosis (yellowing leaves), feed hydrangeas with Epsom salts followed by a dose of iron chelate. To boost them, foliar feed with Trelmix which contains micronutrients.
Every gardener has their own method. What’s important is not to remove the flower buds which develop on the wood of the previous year’s growth. As a general rule just trim off dead heads during summer leaving the plump, uppermost, buds. In winter (July/August), remove any dead wood and thin stems. On old or mature plants, take out a couple of old thick woody stems at the base to open up the plant and encourage fresh new stems. Then cut back the remaining stems to just above the first healthy pair of buds. Young plants will only need a light trim.
FOR THE VASE
Select only mature, fully open ‘flowers’. Cut long stems with some woody stem, then recut into the soft wood under water. Immerse the entire flower head and stem in water (the bath is a good place), for a couple of hours before arranging them. A little alum added to the water will help prolong their life.
You can also dry mature flower heads. Remove all the leaves and hang upside down in a breezy but warm, dry place.
Traditionally gardeners grow new plants from hard wood cuttings taken in autumn or after pruning. However they are easy to propagate from soft wood tip cuttings taken in summer and these grow remarkably fast.
Growing hydrangeas from soft wood tip cuttings or semi-hard slips in summer is quick, easy and rewarding. The bonus? If you have a hydrangea with large bracts or great colour, any plant you propagate from it will have the same traits.
- Take 15cm long cuttings from healthy hydrangea bushes selecting non-flowering, young green stems. It’s best to do this in the morning when the plants are well hydrated. Make the cut just above a node. Keep the cuttings in a cool place in a plastic bag until you’re ready to pot them up.
- Use a suitable, free-draining but moisture-retaining commercial potting mix. Or make your own by mixing equal parts of moistened palm peat (obtainable from nurseries in compressed peat blocks) and coarse river sand or perlite. Moisten it before filling several clean, 8–10cm diameter pots.
- Using a sharp blade, cut off all the leaves with the exception of the top pair of leaves surrounding the top bud.
- Now recut the stems at a slight angle, just below the upper leaf node where you’ll see a pair of new buds developing in the axil of the stubs of the leaves you’ve just removed. If you want to propagate more plants, save the portion you’ve cut off and make similar cuts beneath and above each node.
- Dip the end of the prepared cuttings in a hormone rooting powder or liquid specifically for semi-softwood cuttings and then tap to remove any excess.
- Place each cutting in its own pot to a depth of about half the stalk and firm into place by pressing down the potting mix gently.
- Water lightly.
- Cover each pot with a plastic bag; you may need to put in some sort of support like a piece of wire coat hanger to prevent the plastic touching your cutting.
- Secure the plastic bag with a piece of twine or an elastic band. Place the pots, on drip trays, in a shady, but bright place; never in the sun. Check periodically that the potting mix is moist; if not, water as necessary.
PLANTING OUT YOUR NEW HYDRANGEAS
Once the cuttings have begun to root, remove the plastic bag and water them when needed. This should be in about 3 – 4 weeks. Begin to feed the plants with a weak solution of Kelpak and Seagro or similar water-soluble fertilizer. Once the roots begin to emerge from the base of the pot, they’re ready to be planted into a larger pot until they’ve established a good root system and can then be planted out in the garden.
Pruning hydrangeas in pots
Prune and shape bigleaf hydrangea as soon as blooming stops in midsummer. Although oakleaf hydrangea rarely requires pruning, light shaping is best done after the blooms begin to fade in late summer. Prune peegee hydrangea and smooth hydrangea more drastically by cutting the plant down to 6 to 12 inches from the ground in early spring.
Both can also remain unpruned, as blooms will develop on the new growth. All hydrangeas benefit from deadheading, which involves removal of blooms as soon as they wilt. Deadheading promotes continued blooming and keeps the plant looking tidy until the next bloom cycle.
Water Hydrangea in Pots
Although hydrangeas may tolerate dry soil for a short time, they require a generous amount of water to perform their best. Dry potting soil may result in stress and dropping of leaves. This is especially true of container-grown hydrangeas because in pots, soil tends to dry out quickly. Hydrangeas grown in full sunlight require more water than hydrangeas exposed to afternoon shade, as the strong sunlight can evaporate the moisture in the plants’ soil quickly.
When kept indoors, hydrangeas must be planted in containers with a drainage hole and a lightweight, well-draining potting soil because poorly drained soil may result in rot and other diseases. To water hydrangeas, water deeply until water runs through the drainage hole. Always water immediately if the plant begins to look wilted.
How much light does Hydrangea need
Light requirements for hydrangeas in pots vary depending on the variety. Panicle hydrangea (Hydrangea paniculata), also known as peegee hydrangea, and smooth hydrangea (Hydrangea arborescens), thrive and bloom their best in full sun and may become leggy and unattractive with too much shade. Oakleaf hydrangea (Hydrangea quercifolia), and bigleaf hydrangea (Hydrangea macrophylla), benefit from afternoon shade, especially in climates with hot summers. For these varieties, too much sun may scorch the blooms and cause the leaves to sag.
Fertilizing Hydrangea in Pots
Hydrangeas benefit from an application of a general-purpose, controlled-release fertilizer in spring. Usually, one annual application is enough to sustain the plant, as too much fertilizer may create a lush, fast-growing plant with few blooms. The right amount of fertilizer for a plant depends on the plant’s variety and its size.
Using too much fertilizer in a hydrangea pot can also make the plant more susceptible to damage by insects. Apply a second application in midsummer if growth appears slow or if the foliage appears pale. Alternatively, hydrangea benefits from more frequent applications of a general-purpose, water-soluble fertilizer in place of controlled-release fertilizer. Because rate of application varies, it’s critical to read the label carefully for specific instructions.