Rhododendron Johnnie Johnston

(H4) Attractive semi-double soft rose pink flowers, stained with a darker shade in the centre. April flowering. Bred in Cornwall, suitable for mild climates and cool conservatories. Height 50-75cm in 10 years. Requires moist acid composts.

Bred by Sir Edward Bolitho at Trengwainton, which is now a choice National Trust garden in Cornwall.

• Easy to grow, but give winter shelter.
• Ideal position: needs careful site selection.
• Parentage: johnstoneanum (double form) x tephropeplum.
• Hybridization date: pre 2000.
• Ideal soil: pH 4.5 to 6.0
• RHS Hardiness Rating: H4.
• How we usually propagate this plant: Cutting.

Good to know

Tender

Tender (maddenia) Rhododendrons are suitable for the cold greenhouse and mild areas such as Cornwall where they can be grown outdoors. Elsewhere in sheltered gardens they are worth trying against a South facing wall if temperatures are unlikely to go below -5°C. They give a magnificent display in spring, and the pinks and whites often have gorgeous scent to fill a conservatory. Many of these rhododendrons are epiphytic, meaning that they naturally grow in the boughs of forest trees and rock crevasses. Hence they often grow and flower better when their roots are constrained in a relatively small pot, and they need a very free draining (orchid type) compost, with just a teaspoon of slow release fertilizer.

When grown in a conservatory, these plants grow vigorously, so prune hard straight after flowering to encourage bushiness, leaving only about 10cm of the previous year's growth. They much prefer to be grown outside during summer months where there is fresh air and rainfall, so try to move out after frosts in May, and bring back indoors in October or November. Heating is usually not needed in the UK, and plants can be easily scorched if placed too close to radiators or heaters, or where there is lack of air movement within a conservatory.

Please note: Watch out for sooty mould on plants grown under protection (see advice centre for further information).

The Basics

Ideal soil

Acidic soil, good organic content, pH 4.5-6.0. Inkarho range of rhododendrons will tolerate soils up to pH7.5

Sun or Shade

Light dappled shade is best for most varieties.

Shelter

Refer to hardiness rating. Give young plants protection.

Site Selection

Avoid close to trees, roots, invasive weeds, walls, hot patios, dry banks and waterlogged soils. Do not use weed matting or stone mulch.

Plant spacing

Use the height shown in 10 years as a guide to the distance between each plant. Allow room for plant to fill out. If planting closer for instant impact, be prepared to move plants after a few years.

Compost

• 3 litre pot, dig in 10-20 litres of ericaceous compost.
• 7.5 litre pot, dig in 20-30 litres of ericaceous compost.
• 70-80cm specimen, dig in 60 litres of ericaceous compost.
• 100-120cm specimen, dig in 120 litres of ericaceous compost.

Planting depth

Plant high in the ground, with the top of the rootball visible.

Feeding

Slow-release ericaceous feed recommended in March and straight after flowering.

Mulch

Recommended every few years.

Water

The key ingredient! Keep moist all season, especially the critical time at end of June for flower bud initiation. Tap water is better than no water. Heavy dose at least once per week in dry weather.

Drainage

Ensure good drainage in winter, especially with yellow flowering varieties. Avoid waterlogged sites.

Pruning

Rhododendrons and Camellias: Not normally required. Tidy wayward shoots after flowering.

Evergreen azaleas and Bloombux can be clipped into a low hedge.

Magnolias and Acers: Formative pruning when young to shape into a tree or bush.

Deadheading

Remove old flower-heads, particularly on young or weak plants.

For further advice see here

Size Guide

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