Douglas' phlox

Douglas' phlox: how do you recognise it?

Habit

Low, dense cushion about 10 cm high and 40 cm wide, with much-branched, prostrate stems.

Leaves

Narrow, needle-like to linear, about 1–2 cm long, firm and green all year.

Flower

Flat, five-petalled little flowers about 1 cm across, in April and May, so numerous that they cover the foliage.

Colour

White, pink, lilac or purple, sometimes with a darker centre; cultivars differ.

Roots

Shallow and fibrous. It needs well-drained soil.

Flowering: April–May · Plants: March–April and September–October · Pruning: May

Why grow it?

• Flowers so freely in April and May that the cushion almost disappears under the blooms.
• Stays green all year and forms a dense mat that gives weeds little chance.
• Early nectar source: bees find food here as soon as spring arrives.
• Well suited to dry, sunny spots such as the rock garden, dry wall, trough and gravel border.
• Fully hardy (to about −30 °C) and little work.

Douglas' phlox: where does it grow best?

• Full sun. In shade the cushion opens up and flowers less.
• Lean, well-drained soil: sand or loam, acid to neutral. It will not tolerate wet, heavy clay.
• Dry to slightly moist: it copes well with drought, but not with wet feet.
• Suits a rock garden, dry wall, trough, gravel border or the edge of a path.
• Allow 30–40 cm per plant; 25–30 cm if you want it as ground cover.

Light

Sun

Soil type

Sand or loam

Acidity

Acid or neutral

Moisture

Dry

Size

0.1 m tall, 0.4 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Aubrieta: Flowers at the same time in purple and blue, in the same sun and dry soil.
• Stonecrop: Fleshy foliage that keeps the rock garden attractive later in the season.
• Grape hyacinth: Small blue spring bulbs that come up through the cushion.
• Saxifrage: A low plant with cushions of quite different foliage, perfect for the rock garden.

Douglas' phlox: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or in September–October, when the soil is neither frozen nor waterlogged.
2. Choose a sunny spot. Lighten heavy soil with coarse sand or fine grit; in a rock garden a layer of grit under the roots helps.
3. Dig a hole as deep as the pot and a little wider, and set the plant at the same depth as in its pot.
4. Space plants 30–40 cm apart, or 25–30 cm for a mat that fills in quickly.
5. Water straight away and keep the soil slightly moist for the first weeks.
6. Spread a thin layer of fine grit or chippings around the cushion. Do not put compost over the foliage.

Care

Watering

Only in the first year in dry weather. After that it almost always looks after itself.

Feeding

Hardly needed. On very poor soil, a thin layer of compost in spring; too much feed gives soft foliage and fewer flowers.

Mulching

A thin layer of fine grit or chippings keeps the soil under the cushion dry and the flowers clean.

Spent flowers

Cut back the flowering tips straight after flowering (see pruning).

Weeding

Remove weeds and grass from the cushion in good time: once they are growing through, they are hard to get out.

Tip: Trim the cushion back by about a third straight after flowering: it stays dense and compact and flowers freely again next year. Without good drainage it struggles through a wet winter.

Douglas' phlox: when to prune it?

Pruning months: May.

When: Straight after flowering, usually in May.

How:

• After flowering, trim the flowering tips back by about a third with shears, down to the young foliage.
• This keeps the cushion compact and dense and encourages new shoots.
• Remove dead, brown pieces in the middle of the cushion.

Caution: Do not cut into bare, old wood: it is slow to shoot again from there.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Cuttings

Late May–July: 3–5 cm cuttings from young, non-flowering tips, lower leaves removed, in sandy potting compost. Keep them moist and out of full sun; they root in a few weeks.

Division

After flowering or in September: lift a piece with roots from the edge of the cushion and plant it elsewhere.

Douglas' phlox: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: no protection is needed in Belgium.
• The cushion stays green in winter. Wet winters are more of a problem than frost, so good drainage matters most.
• In a pot or trough: use a gritty, free-draining mix and keep it outdoors in a sheltered spot, so the soil never becomes soggy.

Diseases and pests

• Bare centre: The cushion dies out in the middle, most often through too little sun, soil that is too wet, or age. Cut it back, give it more light, or divide and replant.
• Rot in wet soil: Brown, soft patches after a wet winter. Improve drainage with grit and remove the affected pieces.
• Spider mite: In hot, dry weather the foliage turns dull with fine webbing. Spray the cushion with water and water at the base during drought.
• Powdery mildew: White powder on the foliage in damp summers or in a spot that is too sheltered. Give it more air and cut off affected parts.

Through the year

• March: Plant. Remove weeds from the cushion.
• April: Flowering begins. Plant.
• May: Full flower. After flowering, trim back by a third.
• June: Take cuttings from young, non-flowering tips.
• July: Cuttings. Water young plants in dry weather.
• September: Plant or divide.
• October: Plant. Weed the cushion.
• December: Rest. The cushion stays green.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The species is named after David Douglas, the Scottish plant collector who travelled across the west of North America in the first half of the 19th century. The Douglas fir is named after him too.
• The name Phlox comes from the Greek word for ‘flame’.
• Although it belongs to the same genus as the tall garden phlox, this is a mountain plant that actually likes lean, dry soil.