Rhododendron semnoides

This is a rare plant with superb creamy white flowers flushed rose in April. The lower surface of the large leaves (up to 25cm) are covered with whitish to buff indumentum. It may be a natural hybrid between R. praestans and R. arizelum. Height 150cm in 10 years.

Big leaf Rhododendron species have great architectural foliage which looks stunning in a woodland glade or city courtyard garden. However, the lovely large leaves do need protection from winds, especially cold winds, to prevent them being marked or damaged. Strong winds can even snap off these big leaves at the petiole (leaf stalk) or midrib and ruin the plant. Carefully choose a sheltered, moist but well drained position, and you'll grow a fantastic foliage plant with the bonus of wonderful flowers after 6 to 10 years.

• Recommended for lovely foliage.
• Plantsman range.
• Ideal position: Sheltered woodland or shaded courtyards, avoiding cold winds.
• Habit: tree-like.
• Group: Species Rhododendron.
• Subsection: Falconera.
• Introduction date: pre 1950 (1922).
• Species distribution: SE Tibet.
• Approximate altitude: 3,700 to 4,000m.
• Ideal soil: pH 4.5 to 6.5.
• RHS Hardiness Rating: H5.
• How we usually propagate this plant: Seed.

Good to know

Wonderful architectural plants with huge leaves up to 60cm long! These are choice woodland Rhododendrons needing the very best sheltered positions to allow them to grow to their full stature of up to 5 metres. As a bonus, flowering will typically start after 6 years, but can take up to 10 years. Big leaved Rhododendrons are among the more tender of our range, but are well worth trying if you have the correct conditions. They are best suited to sheltered woodland in the milder regions of the UK, though they can also be used as feature plants in sheltered courtyard gardens. Winter protection is recommended for young plants.

Rhododendrons like moist acidic soil, with good drainage, and plenty of organic matter such as leaf-mould and added ericaceous compost. Big-leaved species should be given the best planting positions, which are neither too wet nor too dry. For a guide to plant spacing, use the height we give in 10 years as a guide to the distance between each plant, or approximately 1 plant per 3m². Plant no deeper than the top of the rootball, and dig in plenty of good ericaceous compost around the sides. A teaspoon of slow release feed is sufficient for a 3 litre plant, rising to a small handful for a mature plant. Plants can be grown as single stemmed trees, or the leader can be pruned as a young plant to encourage a more bushy habit. You may need to give protection from deer rubbing their antlers on the stems

Please note: Big leaved Rhododendrons need to be sheltered from wind to prevent the large leaves being broken off at the petioles (stalks) during gales. Moisture control is critical to prevent moisture stress and misshapen leaves, so we do not recommend them being grown in pots.


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Size Guide

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.

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