How to grow petunias
All you need to know about growing bedding petunias, in our Grow Guide.
Petunias are some of the most outstanding bedding plants, thanks to their knack for creating a vibrant mass of colourful summer blooms. Petunias are versatile, ideal for different types of pot or hanging basket as well as in the ground. Originating from South America, petunias are frost tender and make a splendid display through summer and into autumn, often right until the frosts arrive.
Petunias are divided into two main types: compact bushy petunias with an upright habit, and trailing petunias with stems up to 90cm long. Within both groups there's a huge choice of colours and flower shapes to choose from. Colours range from ultra-brilliant pinks, reds, and purples, to soft pastel shades and white. The size of the flowers ranges, too, and you can choose varieties with ruffled edges and bi-coloured blooms, along with single- and double-flowered varieties.
How to grow petunias
Petunias can be raised from seed, bought as small plug plants to grow on, or bought as garden-ready plants. Petunias are tender and won’t tolerate any frost at all, so you mustn’t plant them outside until late spring or early summer.
Petunias need a good 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. For raised containers like hanging baskets and window boxes that are exposed to drying sun and wind, choose a compost that includes water-holding granules.
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Spacing of petunias depends very much on their growth habit and ultimate size as well as where they are being grown. 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.
Where 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.
The immense versatility of petunias means the growing habit of different types can be matched with almost every type and size of pot and container.
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.
How to care for petunias
Regular watering is important and is vital 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 fertilizer high in potash (such as tomato fertilizer). If plants are looking tired come autumn, switching to a high-nitrogen fertilizer can boost growth for the last few weeks before the frosts.
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. Feed at the same time which will boost new growth.
How to propagate petunias
Petunias can be grown from seed although they’re not the easiest of plants to propagate. Seed should be sown in late winter at a temperature of 21°C. Light is needed to germinate petunias so don’t cover the seed: sow onto the surface of moist compost and cover with polythene or put in a propagator, to ensure the seed doesn’t dry out. Seedlings need a warm and well-lit growing environment, shaded from direct sun, with a temperature no lower than 13-15°C.
Buying plug plants of petunias can be a good compromise between raising from seed and buying more expensive garden-ready plants. Plug plants are supplied by mail order in early to mid-spring. Pot them individually into 9cm pots and grown on a well-lit windowsill or in a heated greenhouse, only planting out after hardening off and when all danger of frost is past.
Some petunias, principally trailing varieties, can be kept over winter if cut back and brought into a warm environment. If space is limited, root cuttings 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. Aphids may occur on the young leaves and stems: inspecting plants regularly and hand-squashing small infestations can stop them becoming established. Otherwise, there are various ready-to-use sprays to combat aphids.
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.
Advice on buying petunias
- Choose the right petunia for your needs - cascading varieties are best for pots and containers, while upright vareities are best for bedding schemes
- Choose a mix of colours that complement each other
- You can buy petunias at garden centres but you'll have a greater variety at specialist nurseries and online
Where to buy petunias
Petunia varieties to grow
Petunia ‘Frenzy Mixed’ is an upright, bushy petunias, bearing masses of plain and striped flowers on compact, upright, bushy plants.
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.
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, to 50cm.
Petunia Surfinia series is vigorous and free flowering, bearing a profusion of blooms in colours ranging from white and pastels to vibrant primary shades. Up to 90cm long.
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). Height 30cm, spread 50cm.
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