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
- 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: No
- Good for cut flowers: Yes
calendar
seasonal checklist
spring
- Sow petunia seed under cover in early spring.
- Pot on rooted seedlings and keep somewhere light and frost-free.
- Plant out after risk of frosts has passed.
summer
- Deadhead as necessary.
- Water regularly when the top two inches of soil feels dry.
- Add a liquid feed when watering.
autumn
- Take cuttings to overwinter.
- Move perennial plants to a frost-free place.
winter
- Plan which varieties you’d like to grow next year.
how to plant & grow petunias
where to grow petunias
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 petunias
Sow petunia seeds indoors in February-April. Pot on and move to a cooler position before planting out after the last frosts.
sowing petunia seeds undercover
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.
planting our seedlings
For the best results, we recommend potting these on into 9cm pots (or similar), before planting in their final position outside.
1. Choose a good quality, multi-purpose, peat-free compost and mix with a small amount of horticultural grit to ensure good drainage.
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.
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.
4. Check that the roots are fully covered and tamp down the soil gently. Give the pot a tap to settle the soil.
5. Water well and place in a greenhouse, cold frame or suitably sheltered spot outside to grow on.
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.
planting our 9cm potted plants or larger plants
IN THE GROUND
We’ve done a bit more of the legwork here for you, so if conditions are right, you can plant these straight into your containers or the garden by following the instructions below. If weather conditions aren’t right (i.e., they are too cold or too wet) then you can pot them on into a 1 or 2 litre pot before planting.
1.Prepare the ground (ideally at least two weeks before planting) by forking over the soil and incorporating plenty of organic matter such as homemade compost or well-rotted manure. Remove weeds and large stones as you go.
2. Water your plants well before planting. You can also soak them for 20 minutes in a bucket or wheelbarrow of water if they seem particularly dry.
3.Rake the area to level it and produce a fine crumbly soil texture or tilth.
4. Dig planting holes deep and wide enough to cover the roots. Adding rootgrow into the bottom of the planting hole will help plants establish roots
5. Place the plant in the hole so it sits at the same level as it was in its previous pot and firm the soil around it to anchor it. You should be able to tug gently on the leaves without the planting lifting out of the ground.
6. Water well, and once it looks like all the water has been absorbed, water again with a really good amount of water (not a sprinkle). Do this every 5-7 days (if there has been no rain) to encourage roots to be drawn down deep into the ground, resulting in stronger plants.
7. Remember that plants tend to look better in groups of three, five or seven, and allow about 15-40cm between plants in the ground, depending on the variety.
IN A CONTAINER
1. Choose a pot large enough to give the roots space to grow and spread. Plants in terracotta pots will need more watering due to the porous nature of the material.
2. Make sure you have plenty of drainage holes in the containers and broken pottery at the bottom to prevent the drainage holes from blocking.
3. Fill your chosen container with fresh, peat-free multi-purpose compost.
4. Dig planting holes deep and wide enough to cover roots and position the plant in the hole so it sits at the same level as it was in the original pot. Fill the space around the plant with soil, pressing firmly so the plant can’t be easily lifted.
5. Water well and add more compost if the surface has sunk more than an inch below the rim of the pot.
6. Keep well-watered and place in a warm sunny spot and feed regularly during the growing season for the best results.
how to care for petunias
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.
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 & arrange petunias
Cut fresh blooms in the morning or evening and place straight into a vase where they’ll last for 4-6 days.
