How to plant, grow & care for Petunias

We’ve trialled hundreds of container plants at Perch Hill over the years, and petunias – and their closely related cousins, calibrachoas and petchoas (hybrids of the two) – are always at the top of the list. Available in a kaleidoscope of colours from white to almost-black, via sunset oranges and mouth-wateringly rich wine reds, they’re super easy to care for and flower long and hard until the first frosts. Use them in hanging baskets, around the sides of pots to soften the edges, or simply on their own as a sensational centrepiece. They’re great in the ground too, so pick a spot you’d like to fill, and choose from our range of seeds, rooted cuttings and young plants to find the perfect one for you.

Details Where & when to plant How to sow How to plant Care guide Pests, diseases & common issues Frequently asked questions

Details

Calendar

Jan J

Feb F

Mar M

Apr A

May M

Jun J

Jul J

Aug A

Sep S

Oct O

Nov N

Dec D

Sowing

Planting

Flowering

Where & when to plant

Where to plant

Soil type

Petunias prefer a fertile, well-drained soil.

Aspect & position

Petunias need full sun (at least six hours a day) to thrive.

When to plant

Sow petunia seeds indoors in February-April. Pot on and move to a cooler position before planting out after the last frosts.

How to sow

Start petunia seeds undercover in late February-April.

Fill divided seed trays or Jiffy modules with peat-free compost and moisten well. Sow thinly onto the surface and place in a propagator or on a warm windowsill (a temperature of 20C is ideal), and cover with a clear plastic bag or sheet of glass to maintain a humid atmosphere.

Once germination occurs, remove the lid/glass/polythene, and place the tray in a light, cool place such as a cool windowsill is ideal. If more than one seed per module has germinated, remove the weaker seedling. Water sparingly.

When you can see roots filling the bottom of the module, pot the seedlings on into 9cm pots, pinching out the growing tips when the plant is about 8cm tall to encourage bushier growth. If the plant develops any flowers or buds while still small, pinch these out too. Plant out after the frosts, hardening the plants off over 1-2 weeks before you do so.

Photography by

Jonathan Buckley

How to plant

For the best results, we recommend potting these on into 9cm pots (or similar), before planting in their final position outside.

Step 1.

Choose a good quality, multi-purpose,peat-free compost and mix with a small amount of horticultural gritto ensure good drainage.

Step 2.

Fill a clean 9cm pot with the potting mix and firm down gently. Use your fingers or a dibber to make a hole in the middle, slightly deeper than the seedling. Top tip – always handle seedlings by the leaf, not the stem so you don’t damage the lifeline of the plant.

Step 3.

Position the seedling in the hole, ensuring the roots are fully covered and that the seedling is firmly placed, tapping to settle the soil. Top tip – always handle seedlings by the leaf, not the stem so you don’t damage the lifeline of the plant.

Step 4.

Check that the roots are fully covered and tamp down the soil gently. Give the pot a tap to settle the soil.

Step 5.

Water well and place in a greenhouse, cold frame or suitably sheltered spot outside to grow on.

Step 6.

Once the plants are growing strongly and the roots have filled the pot, plant out (once acclimatised and once the last frosts have passed) following the steps below.

Photography by

Jonathan Buckley

Care guide

Watering

Water your petunias regularly, especially those in pots which are more likely to dry out more quickly. Petunias don’t like to sit in wet soil though, so you need to strike a balance. Water at the base of the plant rather than over the leaves to avoid sun scorch and fungal problems.

Fertilising

Feed plants every two weeks during the growing season with a high potash fertiliser to promote flowering.

Deadheading

Many of the modern varieties do not need much deadheading, but removing any faded flowers will help keep plants looking their best. Pinch just below the petals to remove the seeds as well.

Propagating

Petunias can be propagated via cuttings from mid-summer to mid-autumn, following the steps below:

On a dry morning, choose leafy, flower-free shoots about 10-12cm long. Cut cleanly and place in a plastic bag to prevent them drying out.
Trim to just below a leaf node and remove the lower leaves so that just a few remain. Pinch out the tip.
Fill a container with peat-free potting compost mixed with 50 percent sand or grit and push in the cuttings deeply around the edge of the pot, taking care that they don’t touch each other.
Water well and move to a cool place out of direct sunlight.
Monitor to ensure the soil stays moist (but not wet).
Pot up plants when you see roots emerging through the base of the pot, remembering to keep them protected from frost over winter.
Plant out in May, once all risk of frost has passed.

Overwintering

Some petunias, especially the trailing varieties, and petchoas will overwinter if they are cut back and moved indoors before the frosts.

Pests, diseases & common issues

Aphids

While aphids can spread viruses (see below), they are beneficial to lacewings, ladybirds and hover flies which feed on them so live with them if you can. If not, squash them, or hose them off. At Perch Hill, we use a homemade garlic spray as a preventative. To make it, take a whole garlic bulb and blitz it in a processor. Add 250ml of water and then blitz again. Add 750ml of water and allow to infuse overnight, before decanting into a spray bottle for ease of use.

Slugs & snails

Slugs love the soft leaves of petunias, so allow plants to grow to a good size before planting out, and consider using barriers (such as copper tape around pots) or wool pellets to deter them.

Cucumber mosaic virus

Petunias can be prone to cucumber mosaic virus, which causes mottled, yellow leaves and stunted growth. If your plant has the virus, remove it from the soil and dispose of it.

Deer

Deer will eat petunias, so protect them with fencing if deer are a problem in your area.

Why do petunias get leggy

There are several things you can do to stop your petunias getting leggy and to encourage them to form nice plump clumps instead. Ensure they are in a sunny spot and keep on top of watering, making sure your soil is neither too dry nor too wet. Deadhead regularly, removing the seedpods (just below the flowers) as you do so, and regularly cut back the stems by between a quarter and a half to encourage regeneration. Overfeeding can also be an issue, as nitrogen encourages leafy growth, so cut back on feeding or switch to a feed containing more potassium.

Why are my petunias wilting or dying

Petunias are generally trouble-free plants but if yours are wilting or dying, it may be due to overwatering, which can lead to root rot, or due to a viral disease such as cucumber mosaic virus (see above). Give your plants a bright, sunny spot and water regularly, allowing the top of the soil to dry out in between.

Why are my petunias sticky

Many petunias have naturally sticky leaves. Excessive stickiness can also be due to an aphid or whitefly infestation, so keep an eye out and remove the insects as necessary.

Photography by

Jonathan Buckley

Frequently asked questions

Can petunias survive winter?

Some petunias, especially the trailing varieties, and petchoas will overwinter if they are cut back and moved to somewhere frost-free.
Can I grow petunias indoors?

Petunias are best grown outdoors in bright light. Perennial varieties should be overwintered indoors in a frost-free spot, and seeds should be started undercover between February and April.
Which petunias are trailing?

Many types of petunias, including those in the ‘Surfinia’, ‘Cascadia’ and ‘Wave’ series, are trailing.
Which petunias are perennial?

There are a number of perennial petunias but since most are tender or half-hardy, they tend to be grown as annuals in the UK.
Do petunias spread?

Yes, many petunias are spreading plants making them great for ground cover, pots and hanging baskets.
Are petunia flowers edible?

No, it is not advised to eat petunia flowers.
Are petunias toxic to cats or dogs?

No, petunias are not toxic to cats or dogs.
Are petunias hardy?

No, petunias are not hardy and should be kept inside over winter and only planted out after the risk of frost has passed.

What to grow with Petunias

Petunias look great generously planted in pots or in the ground on their own, or in combination with all sorts of plants. At Perch Hill, we like mixing them with cosmos and salvias in similar hues (try our fabulous carmine and crimson combination that will go on for months), or with striking contrasting colours as in Arthur Parkinson’s Flower Yard Collection featuring lime green nicotiana and sparkling fountain grass.

How to cut and arrange Petunias

Cut fresh blooms in the morning or evening and place straight into a vase where they’ll last for 4-6 days.

Common name	Petunia
Latin name	Petunia
Type	Half-hardy perennials and annuals grown as annuals in the UK
Height	30cm
TLC rating	Easy
Aspect	Full Sun
Planting position	Borders (front), container garden, hanging baskets
Suitable for pots	Yes
Good for pollinators	Yes
Good for cut flowers	Yes

How to plant, grow & care for Petunias