How to grow petunias

Petunias need plenty of sun, a fertile soil, and shelter from strong winds. In hot summers or milder areas of the country, petunias will also do well in partial shade.

Grow trailing petunias in hanging baskets, raised pots, or pots and window boxes, where their stems and flowers can trail over the sides. They make unusual and colourful ground cover in borders and can also be planted to tumble down slopes, banks, and from raised beds.

Grow bushy, upright petunias in pots or the ground, either as part of a colourful bedding scheme or to fill gaps between more permanent plantings, in a border.

When to plant petunias

Petunias are tender plants, so wait until all risk of frost has passed before planting outside. This is usually late spring to early summer, depending on where you live.

If growing petunia from seed, sow in early spring under cover, and then harden off plants before planting out in May or June.

How to plant petunias

Petunias can be raised from seed, bought as small plug plants to grow on, or bought as garden-ready plants.

To grow from seed, fill a seed tray with peat-free seed compost mixed with vermiculite or perlite. Sow petunia seed on the surface of the compost and don't cover it, as it needs light to germinate. Then pop it in a propagator with a lid to help keep the compost moist. Place in a warm room or use a heated propagator set to 18-24ºC.

Plant the seedlings into individual pots once they have two true leaves, and then keep in a cool, frost-free spot such as a cold frame to grow on.

Pot up plug plants to grow on in the same manner as above.

Before planting petunias outside, harden them off by gradually acclimatising them to the outside over a week or two. When buying garden-ready plants, check if they’ve spent any time outside or whether they’ve been under cover, in which case they’ll also need hardening off before planting out.

Petunias need rich soil to perform well. In borders, prepare the soil by mixing in plenty of well-rotted compost or soil conditioner. For pots and containers, petunias do best in peat-free, multi-purpose potting compost.

In pots and containers, petunias can be massed close together to produce a spectacular show in a short time. Elsewhere, the smallest compact and upright varieties can be planted 15-20cm apart, bushy petunias with a lax, mounding habit need wider spacing of around 30cm, and trailing ones spaced around 40cm apart.

How to care for petunias

Regular watering is important for petunias growing in pots and hanging baskets – as a general rule, don't let the compost dry out. In the ground petunias may need additional watering during dry spells.

Direct the flow of water onto the soil rather than spraying the plant, to avoid causing sun scorch on the leaves and flowers. Aim to water early in the morning or in the evening, also to avoid scorching.

Feed every 10-14 days with a liquid fertiliser high in potash (such as tomato fertiliser). If plants are looking tired by autumn, switching to a high-nitrogen fertiliser can boost growth for the last few weeks before the frosts.

Deadhead petunias regularly. Picking off faded and dead flower heads keeps petunias looking good and encourages more flowers to be produced. Trailing varieties that become straggly later in the season can be lightly trimmed.

How to propagate petunias

Petunias can be propagated by saving seed, but the resulting plants may not be true to form, and coiuld be a completely different colour or shape. It's much better to buy fresh petunias each year.

However, you can propagate petunias by taking softwood cuttings from new growth in late summer. Pot the cuttings individually into small pots and keep on a windowsill indoors for winter.

Pests and diseases

Petunias are largely trouble-free, given the right growing conditions and care. You may see aphids on the young leaves and stems, but this is perfectly normal and usually nothing to worry about.

Slugs and snails can be a problem, particularly on petunias growing in the ground. Grow petunias to a good size before planting out as larger plants are much more able to withstand attack. Surround plants with absorbent granules or barriers or use an environmentally friendly bait.

Petunia varieties to grow

Petunia ‘Frenzy Mixed’ is an upright, bushy petunias, bearing masses of plain and striped flowers on compact, upright, bushy plants. Height x Spread: 25cm x 30cm

• Buy Petunia 'Frenzy Mixed' from Thompson & Morgan

Petunia Cascadias series has a range of unusual colours, including ‘Yellow Eye’ (white with a yellow centre), vivid ‘Rim Magenta’, and ’Indian Summer’ that changes colour through shades of yellow and peach. Trailing yet compact. H x S: 50cm x 45cm

• Buy Petunia Cascadia 'Indian Summer' from Sarah Raven

Petunia Surfinia series is vigorous and free flowering, bearing a profusion of blooms in colours ranging from white and pastels to vibrant primary shades. H x S: 25cm x 90cm

• Buy Petunia 'Surfinia Mixed' from Thompson & Morgan

Petunia Tumbelina series have beautifully formed, ruffled, double flowers and, unusually, are scented too. Varieties include ‘Anna’ (bright pink with petals edged with white), ‘Priscilla’ (mauve with purple veins), ‘Candyfloss’ (rich pink) and ‘Joanna’ (pale pink). H x S: 25cm x 80cm

• Buy Petunia Tumbelina 'Most Fragrant Ever' from You Garden

Frequently asked questions

Does petunia come back every year?

Although petunias are perennial, they are tender and will die if exposed to frost. In the UK petunias are treated like annuals and used as bedding plants for one growing season.

Are petunias poisonous to pets?

Petunias are not toxic to pets such as dogs and cats.