Thompson & Morgan Gardening Blog

Petunia ‘Pegasus Wine Splash’ petals are attractively flecked with burgundy
Image: Petunia ‘Pegasus Wine Splash’ from Thompson & Morgan

Petunias are hugely popular bedding plants that you can order as plugs or garden-ready plants. Alternatively, you can sow your own petunia seeds as a cost-effective way to replenish hanging baskets and fill your garden with colour. 

Here, T&M’s resident expert, Kris Collins, shares a few simple tips to increase the flower power and longevity of your petunias. 

Why grow petunias?

Buy scented petunias to add an extra dimension to your displays
Image: Petunia ‘Frills & Spills™ Susanna’ from Thompson & Morgan

Petunias are something I turn to every spring in order to get my garden ready for summer. I couldn’t be without them in my hanging baskets. Trailing types, covered in masses of fragrant trumpet blooms, such as Petunia ‘Easy Wave Ultimate Mixed’, are perfect for lending that luxurious feel to your summer garden.

Most commonly used in container displays, there are actually many varieties that work well in border plantings too. Prolific growth smothers weeds and traps moisture in the soil, whilst also providing a carpet of colour.

Petunias require very little specialist upkeep. As long as you’re prepared to water regularly and remove spent flowers as they go over, you’ll be in for a season of scent and colour right through to autumn.

Which petunia should I choose for my space?

Petunia ‘Back to Black’ produces gorgeous velvety black flowers
Image: Petunia ‘Back to Black’ from Thompson & Morgan

When it comes to choosing your petunias, firstly consider where you want to grow them. Grandiflora types, like Petunia grandiflora ‘Cascade Pink Orchid Mist’ F1 Hybrid, are best saved for basket and container displays – the large blooms are better shown off at height, and will be less prone to weather damage and mud splash.

For a show-stopping petunia bedding display, multiflora types including Petunia ‘Frenzy Mixed’ are the best option. They have smaller flowers and more of them, creating a carpet of colour that will shrug off a summer shower.

How often should I water my petunias?

Keep hanging baskets out of direct sun to reduce water loss
Image: Petunia ‘Surfinia’ Collection from T&M

Watering is very important for healthy petunias. In the height of summer you may need to water containers and baskets twice a day, but at least every other day in an average British summer.

For those that work long hours and have less time for watering, it’s a good idea to move petunia hanging baskets and small containers to a shady spot during heatwave conditions, keeping them out of the afternoon sun until you can get home to give them a drink.

Alternatively invest in an auto watering system to reduce your workload and keep your baskets evenly moist.

Do petunias need deadheading?

Keep petunias blooming by removing wilting flower heads 
Image: Petunia ‘Trailing Surfinia White’ from T&M

Remove spent flowers as often as possible. Don’t just clear away the spent petals, but make sure to remove the entire flower head otherwise seed pods will form, the plant will think it has achieved its objective, and flowering will start to reduce.

Should I feed my petunias?

Petunia ‘Trailing Surfinia Purple’ produces electric flowers and long trailing stems
Image: Petunia ‘Trailing Surfinia Purple’ from T&M

Feed your petunias using a specialist petunia fertiliser for the best results. Add the fertiliser to the compost mix before planting containers and baskets and it will feed your plants for the whole season.

We’ve seen some excellent results with petunias in our technical trials for Incredibloom. Our one-off granular feed, applied at planting time to soils or composts, encourages up to 400% more blooms and provides everything your plants need for up to 7 months – covering the whole growing season.

Can I train my petunias?

Train your petunias by pinching out young growing tips
Image: Petunia ‘Trailing Surfinia Blue’ from Thompson & Morgan

Pinch out the growing tips of your plants during the early stages of growth, and do this two or three times before planting out to encourage side shooting. This will lead to much more compact plants with many more flowers.

By mid-August, some petunia varieties may start to look a little tired and straggly. To encourage a second strong flush of blooms to last well into autumn, cut the whole display back by a third and offer a general purpose liquid feed. Within a week or so the plants will start to bush out again and fresh new flowers will soon follow. Within 2 weeks, just in time for your August Bank Holiday garden parties, the display will again be in full bloom with no sign that it has been pruned.

If you’re growing your petunias from seed, aim to sow plants 10-12 weeks ahead of safe planting. So if you’re generally safe to start planting out bedding plants in your area from the 1st week of June, aim to sow your seeds in the first week of March. I’ll be looking at sowing petunias in more detail before then, so stay tuned!

We hope you’ve enjoyed this post and found our top tips helpful! If you think we’ve missed anything let us know! For even more info, visit our petunias hub page for lots more resources to help you grow and care for petunias. Get your garden ready for summer – check out our summer flowers hub page for advice, inspiration and top tips!

Kris Collins

Kris Collins works as Thompson & Morgan’s quality control manager, making sure customers new and old are kept up to date on the latest plant developments and company news via a wide range of media sources. He trained in London’s Royal Parks and has spent more than a decade writing for UK gardening publications before joining the team at Thompson & Morgan.