Petunias: annual or perennial?
In most garden environments petunias are sold and grown as annuals, typically as bedding plants for beds, hanging baskets and containers. But are petunias really annuals? The answer is no. Technically, petunias are perennials. This is because in warm temperate climates, with no risk of frost and no scorching temperatures, petunias will grown on year after year.
Whilst many people buy and grow petunias as annuals, the fact that they are perennials means that it is possible to take petunia cuttings in summer. As long as these cuttings are overwintered in a warm glass house, conservatory or indoor environment, they will provide new plants for the following year.
Do petunias grow back every year in the UK?
Because petunias are actually perennials they can grow back every year in the UK – if they are not cut down by frost. Usually temperatures below about -2º Celsius (28º F), will kill off petunias. But you can keep them alive with protective fleece or in a greenhouse (with protection) in the winter.
Where winters are mild, petunias may even survive in the garden. I have had one particularly tough petunia specimen come through the winter outdoors in Scotland. Admittedly, it was in a pretty sorry state by March, but it wasn’t killed even though we had some hard frosts. It was in a pretty sheltered position. So I suspect that was what helped it.
On the whole, it is best not to expect petunias to grow back every year in the UK. But, it is worth experimenting with protection and cuttings to see if you can bring some plants through the winter unharmed.
Growing petunias: summary plant notes
Half hardy perennial, typically grown as an annual.
30 cm (1 foot) tall, 30-90 cm (1 to 3 feet wide.
Video: Petunias – annuals or perennials?
What do Petunias look like?
Petunia are vibrant, multi-coloured, bedding plants that will flower for a long period over the summer.
Petunias grow up to around 30cm (1 foot) tall and 60 to 90cm (2 to 3 feet) wide. They have dark or mid green leaves with a hairy, sticky texture, on branching stems.
The main feature of petunias is their flowers which are on show from Spring to late Autumn. Bright and showy, petunia flowers are saucer or trumpet shaped and may be single of double flowered.
The many petunia cultivars mean that there are wide range of petunia flower colours. These mainly cover shades of pink, red, pale yellow, orange, violet blue or white.
Some petunia flowers have darker shading at the centre of the trumpet, some have dark veining across the petals (as in the picture below) and some have dark margins around the lobes of the petals. This latter feature is known as Picotee shading in Botany.
There are 5 main groups of petunia as detailed below. Within each group there are various series. Typically the cultivars in a series are all very similar in size shape and habit with the main variation being the flower colour.
Grandiflora petunias have especially large flowers – up to 10cm (4 inches) wide. However, these flowers are delicate and can be damaged by rain. Therefore, they are best grown in pots or hanging baskets in a sheltered position.
Popular Grandiflora series include the Daddy series, the Express series and the Fanfare series.
These have smaller flowers (up to 5cm, or two inches across) than Grandifloras. They are bushier and, as the name suggests, they produce lots of flowers. Multiflora petunias can also be planted in containers or baskets, but they are tougher than Grandifloras, so will also do well in beds and borders. Popular Multiflora series include Duo, Easy Wave and Surfinia series.
These are a cross between Grandiflora and Multiflora types. They have the large flowers of Grandilfora but with the tougher characteristics of the Multiflora, so they are easier to grow. ‘Wave’ is a popular Floribunda series.
Milliflora petunias are smaller, dwarf plants that arose from a genetic mutation. They have small flowers (4cm, or 1.25 inches) across, but they are produced in their masses. They work well as a contrast to the larger flowered varieties. ‘Fantasy’ and Picobello’ are impressive Milliflora series Petunias.
Spreading petunias are low growing and have trailing stems, with flowers 5-8cm across (2-3 inches). Their spreading habit means they are good for ground cover in your garden beds, but the trailing stems also mean they are effective in hanging baskets.
When, where and how to plant Petunia
Petunias are incredibly versatile plants and can be grown in containers, in hanging baskets or in garden beds.
Since petunias are tender plants, you need to make sure that they are not exposed to frosts. So, plant them out once you are sure that last frost has passed – typically in late Spring or early summer.
If growing petunias from seed or from plug plants, it is best to wait until the plants have bulked up a little, and have several sets of leaves, before planting them in the final position.
If they have been raised in a glass house or heated nursery, make sure you harden your petunias off first. This means placing them outside, in a fairly sheltered spot, during the day, and bringing them back inside at night. Do this for a week or so and, in this way, they can get used to the tougher conditions of the outdoor environment.
Petunias planted in hanging baskets or containers can be packed in fairly tightly to give a spectacular display fast. If planted in borders it is usually best to space the plants 15 to 20 cm (6-8 inches) apart. Particularly bushy or spreading varieties should be spaced 30-40cm (12 to 15 inches) apart.
How to grow and care for petunias in hanging baskets and containers
Ideally petunias need a fertile soil to perform well, although they also need free draining conditions.
It is therefore best to use a multi-purpose compost (ideally peat-free) when planting petunias in hanging baskets or containers.
It is also a good idea, especially where where there is hot sun or wind, to try to find a way to retain moisture within the compost in the hanging basket or container. This might be through using water retaining crystals or by lining the container with plastic. If using plastic lining, make sure there are some holes pierced in so that there is some drainage, as the plants won’t survive if the roots are waterlogged.
Petunias in hanging baskets or containers need feeding regularly. Use a high Potash fertiliser, such as tomato feed, as this encourages flowering
Care for petunias in garden beds and borders
When planting Petunias in your garden beds, enrich the soil first with well rotted manure, compost or soil conditioner.
Keep your plants well watered – though not overwatered – and feed every couple of weeks during summer with a high Potash fertiliser.
How to prune petunias
You can deadhead petunias quite easily by removing the spent flowers as they fade. It is easy to do this by pinching out the dead flower, but it is better to use secateurs or snips to get a clean cut. Cut just above the first set out of leaves below the flower head.
When it comes to pruning petunias, it is important to know that they only produce their flowers at the end of their stems. Therefore, for more flowers, you need are more stems. And how do you get more stems? By pruning your plants.
As the plants grow, they can begin to look a bit ‘leggy’ or straggly. So, when the stems get to around 20cm (8 inches) long, you know it is time to prune your petunias.
You can cut back the stems by about half, again making sure that you cut just above a leaf node. This will encourage the plant to produce new stems from each node, which should quickly start flowering.
If you prune back a few stems every few days, you can keep the plant flowering over the summer and maintain a good shape to it.
Here is what I use for all my pruning:
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- Anvil blade with sap groove, rubber cushion shock aborbers
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Last update on 2023-09-30 / Affiliate links / Images from Amazon Product Advertising API
Martin Cole has been an avid gardener for more than 20 years and loves to talk and write about gardening. In 2006 he was a finalist in the BBC Gardener of the Year competition. He is a member of the National dahlia Society.
He previously lived in London and Sydney, Australia, where he took a diploma course in Horticultural studies and is now based in North Berwick in Scotland. He founded GardeningStepbyStep.com in 2012. The website is aimed at everybody who has been bitten by the gardening bug and wants to know more.
Gardening Step by Step has been cited by Thompson and Morgan, the UK’s largest mail order plant retailer, as a website that publishes expert gardening content.
Check out my comprehensive step by step guide, with plain language explanations and ultra-useful images and illustrations. This is for you if you love dahlias and want to the best out of the dahlias you grow.