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HydrangeaHydrangeas are long-lived shrubs that can be grown in sun or semi-shade, and will also tolerate being grown under large trees. Once established they will reliably produce flowers providing the soil retains enough moisture, so at planting time incorporate copious amounts of organic matter. Hot, dry conditions can encourage problems such as powdery mildew and red spider mite, and wet, humid conditions can promote botrytis on foliage, as well as root and stem rots. A thick mulch laid in early spring will help to retain moisture. Avoid positioning them where they will catch early morning winter sunshine, this coupled with frost can damage new growth. Position them against a wall, fence or hedge can be advantageous providing it is not a frost pocket. Avoid chalky and or acid sandy soils as these can cause chlorosis (yellowing of the leaves). To alleviate this, apply Epsom salts (magnesium sulphate) as a foliar spray at a rate of 20g (¾oz) per litre Do not cut back dead flower heads as these will offer winter protection to the young spring growth. Blue varieties may not produce flowers true to colour, on very alkaline soils. To combat this, ‘dig in’ plenty of peat at planting time, and give a dressing of sequestrine or aluminium sulphate annually. Similarly, pink varieties; tend to be less clear on acid soils. The soil should be dressed annually with lime at 75-100g (2½-3oz) per sq m during winter. Some cultivars will change from pink to blue using a proprietary hydrangea bluing preparation, but only if you have no chalk or lime in your soil. White-flowered cultivars remain white whatever you do. Hydrangeas are prone to attack by red spider mite, capsid bug, aphids and vine weevil. Week 17; summer flowering hydrangeas need no regular pruning. Note; The main cause of non-flowering, especially with mopheads is pruning too hard! Remove the dead flower heads from both Mophead & Lacecaps by cutting back to the first pair of strong, healthy buds lower down the stem. Any frost damaged shoots should be pruned back to just above the first undamaged pair of buds. Remove any weak, straggly stems and cut back to a basic framework if required. An annual mulch of well-rotted manure at this time can also be advantageous. Week 30; Select strong non-flowering shoots and trim to just under a leaf joint, to leave a cutting about 75-100mm (3”-4”) long. Remove all but top pair of leaves. Dip base of cutting in a rooting powder, insert round the edge of a pot filled with a 50-50 compost and sharp sand mix. Place pot/s in a cold-frame to root Note; If cuttings are placed in temperature of 13°- 16°C (55°-60°F) rooting will be much more rapid. When rooted, pot up cuttings into 70mm (3”) pots of potting compost, and over-winter in a cold frame. Pot up as necessary and grow on in a cold frame until planting out time. Week 40; Plant out 1200mm (4ft) apart in humus rich soil.
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