Petunia

Petunia: how do you recognise it?

Habit

Upright or trailing plant 20–30 cm tall and up to 40 cm wide; trailing varieties can make much longer stems.

Leaves

Oval and soft, covered like the stems in sticky hairs.

Flower

Wide trumpets 5–10 cm across, single or double, from May to October.

Colour

White, pink, red, purple, blue-violet, yellow and almost black, plain, veined, striped or with a white edge or star.

Seed

Dust-fine seed in small capsules; it only germinates well in the light.

Flowering: May–October · Sowing: February–March · Plants: May–June · Pruning: May and July–August

Why grow it?

• Flowers for five months, from May until the first frost.
• A huge choice of colours and patterns.
• Trailing varieties fill containers and hanging baskets with a waterfall of flowers.
• Grows fast: a few weeks after planting out, the containers are full.
• Sowing your own in February–March is a fun project and gives lots of plants.

Petunia: where does it grow best?

• Full sun: the more sun, the more flowers.
• Fertile, well-drained soil or potting compost, preferably slightly acid to neutral.
• Normally moist: never let pots dry out, but avoid wet feet too.
• Sheltered from wind and heavy rain, especially for large-flowered varieties.
• Allow 25–30 cm between plants.

Light

Sun

Soil type

Sand, loam or clay

Acidity

Acid or neutral

Moisture

Normal

Size

0.3 m tall, 0.4 m wide

Hardiness

Frost tender: plant out after the last frost (mid-May)

Goes well with

• Lobelia: Small blue flowers at the edge of the container.
• Verbena: Flowers just as long and trails nicely over the edge.
• Zonal geranium: A sturdy, upright partner in the same sun.
• Silver ragwort: Silver-grey leaves that calm the bright petunia colours.

Petunia: when and how to plant it?

Plant in May–June.

1. Sow indoors in February–March at 20 °C and do not cover the fine seed: it germinates in the light.
2. Prick the seedlings out into small pots when they have two true leaves.
3. Harden off the young plants in May: outdoors by day, indoors at night.
4. Plant out after mid-May in full sun, 25–30 cm apart, in fertile soil or potting compost.
5. When planting out, pinch out the tips of the stems once, so they branch better.
6. Water in and mix some compost or slow-release fertiliser into the soil.

Care

Watering

Water regularly, daily in hot weather for pots and hanging baskets. Rainwater is best.

Feeding

From June to September, a flowering-plant fertiliser in the watering can every week; petunias are hungry plants.

Deadheading

Remove faded flowers together with the seed pod behind them, and it will keep flowering freely.

After rain

After a heavy shower the flowers hang limp. Remove damaged flowers; new buds soon take over.

Tip: For spots that catch a lot of rain, choose small-flowered varieties: their flowers recover from a downpour much faster than those of large-flowered petunias.

Petunia: when to prune it?

Pruning months: May and July–August.

When: Pinch out young plants once when planting out in May. If the stems become long and bare in July–August, cut them back.

How:

• When planting out, pinch out the tip of each stem for a bushier plant.
• In summer, cut long, bare stems back by a third to a half, just above a leaf.
• After pruning, water and feed; within two to three weeks it is in full flower again.
• Do not cut back trailing plants all at once, but a few stems at a time.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

In February–March indoors at 20 °C. Do not cover the seed and keep the compost moist under glass or plastic. It germinates in one to two weeks; the plants flower from June.

Cuttings

In late summer or spring, take tip cuttings 5–8 cm long from non-flowering shoots and root them in moist cuttings compost. This is how you keep a favourite trailing variety.

Petunia: how does it get through the winter?

Hardy to 0 °C: protect in harsh winters.

• Not hardy: frost kills it.
• Treat it as an annual: put the plants on the compost heap after flowering and sow or buy new ones every year.
• You can try overwintering trailing varieties in a light, frost-free place at 10–15 °C, with little water. Cut them back in March.

Diseases and pests

• Aphids: Green or black aphids on young tips and buds. Spray them off with water; ladybirds help too.
• Whitefly: Tiny white flies that rise up when you touch the plant. Hang up yellow sticky traps.
• Iron deficiency: Yellow leaves with green veins, caused by hard tap water or chalky soil. Water with rainwater and repot in fresh compost if needed.
• Grey mould: Grey, fluffy flowers and leaves in long spells of wet weather. Remove affected parts and give the plant more air.
• Slugs: They eat young plants in the border. Picking them off in the evening helps.

Through the year

• February: Sow indoors at 20 °C, without covering the seed.
• March: Sow. Prick out seedlings.
• April: Pot on young plants and keep them light and cool.
• May: Harden off. After mid-May, plant out and pinch out once.
• June: Flowering. Feed weekly and remove faded flowers.
• July: Full flower. Cut back long, bare stems.
• August: Flowering. Cut back if the plants get bare. Take cuttings.
• September: Flowering. Keep watering and feeding.
• October: Last flowers; clear away after the first frost.

Did you know?

• The name comes via French from ‘petun’, a South American word for tobacco. Petunias and tobacco do indeed both belong to the nightshade family, as do tomatoes and potatoes.
• The garden petunia is a cross between two wild species: the white Petunia axillaris, which is scented in the evening and pollinated by moths, and the purple Petunia integrifolia.
• Around 1990, researchers tried to make purple petunias darker by adding an extra colour gene. To their surprise they got white or patchy flowers: a discovery that later helped explain how plants can switch genes off.