Growing and maintaining hydrangeas in the ground in Perth requires managing Perth’s sandy soils and hot, dry summers.
Step 1: Choose the Right Location
- Sunlight: Plant in a spot with gentle morning sun and dappled or afternoon shade. Avoid harsh western sun or exposed hot brick walls, which can scorch the large leaves and flowers.
- Wind Protection: Choose a sheltered area away from strong winds, as hydrangea stems are brittle.
- Spacing: Space plants about 1 to 1.5 meters apart to allow proper air circulation and growth.
Step 2: Prepare the Soil
Perth’s native sandy soil drains too fast and lacks the organic matter hydrangeas crave.
1. Dig a hole twice as wide and the same depth as the pot.
2. Generously mix in compost, well-rotted cow manure, or a specialized soil improver (such as ActivGrow or an acid-loving mix like Searles Azalea, Camellia & Gardenia Mix) to help retain moisture.
3. Add water-retaining crystals to the backfill mix if your soil is particularly sandy.
Step 3: Plant Your Hydrangea
1. Water the hydrangea thoroughly in its pot before planting.
2. Gently tease out the roots on the outside of the rootball if they are tightly bound.
3. Place the plant in the hole so that the top of the rootball sits even with the surrounding garden grade.
4. Backfill with your enriched soil mix and lightly firm it down.
5. Water deeply right away to settle the soil around the roots.
Step 4: Mulch Heavily
- Apply a 5 to 7 cm layer of chunky organic mulch—such as pine bark or sugarcane mulch—around the base.
- Keep the mulch a few centimetres away from the main woody stem (the plant's neck) to prevent rot. Mulch is essential in Perth to keep shallow roots cool and lock in moisture.
Step 5: Watering Routine (Crucial in Perth)
- Establishment Phase: Water every couple of days for the first 4 to 6 weeks while roots settle.
- Summer & Spring: Deeply soak the roots 2 to 3 times a week (ideally in the early morning). Potted or newly exposed plants may wilt quickly on hot days and appreciate an extra drink.
- Tip: Drooping leaves are usually a sign of thirst; they will bounce back quickly once watered.
Step 6: Feeding and Colour Control
- Fertilising: Feed in early spring with a controlled-release flower or rose fertilizer (low in nitrogen, higher in potassium and phosphorus to encourage blooms rather than just leafy growth). Apply a second light feed in midsummer.
- Controlling Flower Color (Mophead Hydrangeas):
o Blue flowers: Require acidic soil (pH 4.5–5.5). Apply an acidifying blueing tonic in spring and autumn.
o Pink or Red flowers: Require alkaline soil (pH above 6.5–7). Sprinkle garden lime around the root zone in spring and autumn.
o Note: White hydrangeas stay white regardless of soil pH, and many modern hybrid varieties have fixed colours that resist shifting.
Step 7: Pruning
- Prune during late winter when the plant is dormant and has dropped its leaves.
- Cut back flowered stems to the first pair of fat, healthy leaf buds (about 1/3 to halfway down).
- Leave any green stems that haven't flowered yet alone, as they hold next season's blooms.
- Remove any dead, weak, or very old woody canes right down to ground level to freshen up the shrub.