Scarlet oak

Scarlet oak: how do you recognise it?

Habit

Open, rounded crown on a straight trunk; 15–20 m tall and 12–15 m wide.

Leaves

7–15 cm long, deeply cut into 7–9 pointed lobes with rounded sinuses; glossy green.

Autumn colour

Bright orange to scarlet, in October–November. Best on acid soil and in the sun.

Flowers

Yellow, hanging catkins in May, along with the leaves. Wind-pollinated.

Fruit

Acorns 1.5–2 cm long, the cup covering the lower half; they ripen in the second year.

Flowering: May · Plants: March–April and October–December · Pruning: December–February

Why grow it?

• Spectacular autumn colour: bright orange to scarlet, from October into November.
• Handsome, deeply cut foliage that stays glossy all summer.
• Becomes an imposing shade tree and a striking specimen in a park or large garden.
• The acorns feed birds and small mammals, and the tree is home to insects.
• Tolerates dry, poor sandy soil and city air pollution better than many other trees.

Scarlet oak: where does it grow best?

• Full sun: that is where it colours best in autumn.
• Acid to neutral, well-drained sandy or loamy soil. On chalky soil the leaves turn yellow (chlorosis).
• Dry to moderately moist; it tolerates dry spells, but not soil that is wet for long periods.
• Allow 12–15 m of space, away from buildings and pipes.

Light

Sun

Soil type

Sand or loam

Acidity

Acid or neutral

Moisture

Dry or normal

Size

20 m tall, 15 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Heather: Likes the same acid, free-draining sandy soil and sun.
• Rhododendron: Evergreen shrub for the light shade under the crown, on the same acid soil.
• Blueberry: A small acid-loving shrub with red autumn colour.
• Sweet gum: A second tree with spectacular autumn colour on acid soil.
• Holly: Evergreen; its red berries and dark leaves look good with the autumn colour.

Scarlet oak: when and how to plant it?

Plant in March–April and October–December.

1. Plant in March–April or from October to December, when the soil is neither frozen nor waterlogged.
2. Choose a young tree of 2–3 m: oaks have a long taproot and establish best when young.
3. Dig a hole two to three times as wide as the root ball, but no deeper. Loosen the sides.
4. Plant at the same depth as in the nursery, backfill with the soil you dug out and do not mix in lime or fresh manure. For a standard tree, add a stake and tie loosely.
5. Water in at once with 20–30 litres.
6. Spread a mulch ring about 1 m wide of leaf mould or bark, keeping it clear of the trunk.

Care

Water

For the first 2–3 summers give 20–30 litres a week in dry spells, deeply and not too often. After that it usually looks after itself.

Feeding

Not needed. Do not use lime or chalky fertilisers: they raise the pH.

Mulching

A mulch of leaf mould or bark keeps the soil moist and acid. Keep the circle free of grass.

Support

For a standard tree, a stake for 2–3 years; remove it afterwards.

Autumn leaves

Make leaf mould from the fallen leaves: a good, slightly acid mulch for shrubs such as rhododendron.

Tip: Plant it in acid, free-draining soil in full sun: that gives the brightest autumn colour. On chalky soil you get yellow leaves and little colour.

Scarlet oak: when to prune it?

Pruning months: December–February.

When: Only when needed, during dormancy from December to February, in dry, frost-free weather.

How:

• In the early years, build up a single leader and a balanced crown: remove competing tops and crossing branches.
• Take out dead or broken branches; cut just outside the branch collar.
• For thick branches and large trees, call in a tree surgeon.

Caution: Do not prune oaks during the growing season, from April to September: fresh wounds are more prone to infection then.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow fresh acorns in October–November where they are to grow or in deep pots; they germinate in spring. Acorns dry out quickly: do not store them. Seedlings can vary, including in autumn colour.

Grafting

Selections with an especially intense autumn colour such as ‘Splendens’ are grafted by nurseries; this is not a garden job.

Scarlet oak: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy to about −30 °C: no protection needed.
• On young trees, a layer of mulch protects the roots during hard frosts.
• Protect the trunk of young trees from game, rabbits and the mower with a tree guard.

Diseases and pests

• Yellow leaves (chlorosis): Pale yellow leaves with green veins on chalky or too neutral soil. Mulch with leaf mould and do not add lime. On strongly chalky soil, choose a different oak.
• Oak processionary moth: Nests of hairy caterpillars on the trunk and branches from May to July. The stinging hairs can cause severe skin irritation. Do not touch the nests and have them removed by an approved contractor or the council.
• Powdery mildew: White powder on young leaves, especially in late summer. Usually harmless on a mature tree; clear fallen leaves and avoid nitrogen-rich fertiliser.
• Weak autumn colour: In shade, in a mild autumn or on chalky soil the colour is less vivid. Provide plenty of sun and acid soil.

Through the year

• January: Remove dead branches in dry, frost-free weather.
• February: Last chance to prune. Check stakes and ties.
• March: Plant once the soil has thawed and is not too wet. Water in well.
• April: Plant. Mulch. The tree comes into leaf.
• May: Yellow catkins. Watch for oak processionary moth nests.
• June: Water young trees in dry weather. Have processionary nests removed.
• July: Water young trees deeply in dry weather.
• August: Water young trees deeply in dry weather.
• October: Scarlet autumn colour. Acorns fall; planting can start again.
• November: Plant. Collect fallen leaves for leaf mould.
• December: Plant. Pruning of dead branches possible.

Good for wildlife

Birds

Berries, seeds or insects as food, or a place to nest.

Did you know?

• The name coccinea comes from Latin and means scarlet, after the autumn colour.
• The deep, rounded sinuses between the lobes tell it apart from the related northern red oak (Quercus rubra).
• It is the official tree of Washington, D.C.