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 given a little shade.

Trailing petunias are ideal for growing in hanging baskets, raised pots, or tumbling over the sides of pots and window boxes. They make unusual and colourful ground cover in borders and can also be planted to tumble down slopes, banks, and from raised beds.

Bushy, upright petunias make superb displays in pots or planted in the ground, as part of a colourful bedding scheme, or to add splashes of vivid colour amongst permanent plants within a border.

When to plant petunias

Petunias are tender plants and can't tolerate any frost, so wait until late spring or early summer to plant them out. The best time to plant them is in May or June, once the danger of frost has passed. Sow petunia seed in early spring under cover.

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, mix some vermiculite or perlite into peat free sowing compost and fill a seed tray. Sow the petunia seed on the surface of the compost as it needs light to germinate and cover with glass or a seed tray cover to help keep the compost moist. Place in a warm room or use a heated propagator.

Prick out the seedlings once they have two true leaves. Once they are in individual pots, move the petunia seedlings somewhere cooler, but frost free, such as a cold frame.

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

In pots and containers, plants 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.

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 need hardening off before planting out.

How to care for petunias

Regular watering is important for petunias growing in pots and containers. The compost mustn’t be allowed to dry out, but at the other extreme, take care not to over-water, either, as this can cause spindly growth. Petunias growing in the ground also need watering during dry spells.

Direct the flow of water onto the soil rather than spraying the plant, to avoid causing sun scorch on the soft leaves and large flower petals. During hot weather, aim to water early in the morning or in the evening, also to avoid scorching.

During summer and early autumn, feed every 10-14 days with a liquid fertiliser high in potash (such as tomato fertiliser). If plants are looking tired come 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 or by taking softwood cuttings. Wait until the seedpods turn brown before collecting the seed and store in a paper bag. The best time to sow is in early spring.

Take softwood cuttings from new growth in late summer. Pot up individually into small pots and keep on a windowsill indoors for the winter.

Growing petunias: problem solving

Petunias are largely trouble-free, given the right growing conditions and care. You may see aphids on the young leaves and stems: inspecting plants regularly and hand-squashing small infestations can stop them becoming established.

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 ‘Phantom’ is an upright, bushy petunia, with velvety black flowers that develop yellow edgings on each petal, giving them a starry appearance. This variety has an upright, mounding growth habit. H x S: 30cm x 30cm

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 some 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.