Horticulture Magazine

Petunia Plant Care & Growing Tips

a flowerbed with purple and pink petunias

Petunia Overview

Official Plant NamePetunia
Plant TypeAnnual Flower
Native AreaSouth America
Hardiness RatingH2
ToxicityNone
FoliageSimple leaves
FlowersVarious colours, trumpet-shaped flowers
When To SowApril, May, June
Flowering MonthsJune, July, August, September, October
When To PruneJuly, August, September
Sunlight

Preferred
Full Sun

Exposure
Sheltered

Size

Height
0.1 – 0.5M

Spread
0.1 – 0.5M

Bloom Time
June – October

Soil

Preferred
Loam, Sand

Moisture
Well drained

pH
Any

Petunias are one of those plants that you can’t fail to notice everywhere in the UK.

These long-flowering beauties add vibrant bursts of colour throughout our gardens with the compact varieties being perfect for borders and beds, while the trailing types are a wonderful addition to hanging baskets.

Petunias come in a wide range of stunning colours, with choices between single and double blooms. Many varieties even have their own unique fragrances.

Brightly coloured petunias in plastic pots sat on a table
Perfectly pretty petunias

With so many options available, it’s easy to see why these pretty perennials are so well-loved, and why they make a choice for any garden whatever its size or style.

Why we love petunias

But why are we so fond of petunias and their trumpet-shaped flowers? Well, here’s a few reasons we can think of:

  • Petunias establish themselves quickly and easily.
  • Caring for them is actually surprisingly easy, making them ideal for beginner and experienced gardeners alike.
  • They are prolific flowerers, producing impressive amounts of blooms from June to October.
  • Petunias are well suited to pots, planters and containers. They won’t look out of place on an exterior windowsill, a patio container or hanging from a decking rail planter.
  • They are low maintenance, making them super easy to care for.
  • With so many colours, sizes and shapes to choose from, it is easy to find the perfect petunias for any garden.
  • Because of their easy to grow nature, they are a great option if you are hoping to introduce children to gardening.

Types of petunias

There are hundreds of types of petunias to choose from, so it can be hard to know where to start when selecting them for your garden. To give you a helping hand, we’ve picked out some of our favourites to help you familiarise yourself with some of the prettiest varieties and help you narrow down the right type for you.

Petunia Priscilla

This double flowering variety of petunia is wonderfully fragrant and has a beautifully unique, large and heavily veined lilac blooms.

This pretty, purple plant has a long trailing habit, growing to up to 80cm in length, making it a superb choice for hanging baskets.

Petunia phantom

This sleek, sophisticated and exceptionally eye-catching variety sport velvety black petals that, over time, develop star-like yellow patterns.

The petunia phantom has a mounding, upright growth habit and is ideal for flower boxes which are sure to turn heads.

Yellow and black petunia phantom
The petunia phantom’s yellow star-like patterns make them real head turners

Petunia red bingo

This plucky little petunia produces bright red medium-sized blooms that add interest to your garden throughout the summer months.

Thanks to their compact, upright growth habit they are perfect for pots that can be placed on patios and decking

Petunia black satin

This petunia produces gorgeous deep purplish-black trumpets that bloom from late spring to late summer.

With their satin sheen and compact nature, they are ideal bedding plants and, will really help to make the other colours in your garden pop.

Petunia star

With blooms in shades of pink, red and purple, petunia stars are one of the most popular bi-coloured varieties. Their whimsical style makes the perfect choice for gardeners who want to inject a bit of fun and gaiety into their garden. Fresh and flamboyant they are well suited to both formal and informal style gardens.

How to grow petunias in the UK

Including petunias in your garden can offer long term colour to your garden’s landscape over the summer months. If you’ve decided they are just what your garden needs, then we have put together a complete guide to growing and caring for petunias.

Let’s get started.

Cultivation

Petunias adore sunshine, although they will tolerate light shade, and will perform best in moist, fertile, well-drained soil. To prepare the soil, you will want to dig in lots of organic matter such as compost or well-rotted manure to make sure you really pack in the moisture.

Sowing and growing petunias from seed

Different varieties of petunias perform differently when sown from seeds so, if you want to plant from seed, it’s important to research which varieties will reward you the most.

Annual and bedding petunia seeds should be sown in spring. Plant the seeds in cell trays, seed trays or small pots and place indoors where the temperature is around 18-24 degrees Celsius.

A gardener planting petunia seeds in a plastic tray
Carefully plant your petunia seeds in cell trays or pots.

When large and sturdy enough to handle without causing damage, you can lift the plants out and place them individually into their own pots or cell trays. Place them in good light in a room where the temperature is around 10-15 degrees Celsius.

Over the next 7-10 days, prior to planting, you can gradually start to acclimatise them to the outside world.

When the plants seem to be comfortable outside and after the risk of frost has passed, you can then plant them in your chosen spot in your garden, containers, hanging baskets or window boxes.

How to plant petunias

The best time to plant petunias is between May and June when the risk of frost has well and truly passed.

You will want to use freshly prepared soil or balancing compost when planting petunias. If you are planting in a basket or pot, we recommend planting three or four plugs per 30cm radius.

Dig a decent-sized hole which will easily allow for the rootball of the plant. Next, add a layer of organic matter or compost to the base of the hole and fork it in thoroughly.

You can then take the root ball and place it in the hole, making sure to adjust the depth so that it is at the same level that it was at in its original pot, taking care to make sure the roots are level with the soil surface. Mix in more compost or organic matter and gently fill in the hole.

Next, we advise applying a layer of general granular feed and then water well. You may also wish to apply a 5cm layer of well-rotted garden compost. This will help you to lock in the moisture and help prevent the growth of weeds.

To begin with water every 3-5 days, avoiding the foliage which can be easily damaged. Instead, water at the base close to the soil.

Take care to ensure that the pots have good drainage to prevent waterlogging and root rot. You can check the moisture level of the soil before watering to avoid drowning your pretty plants.

If you are lucky to have a greenhouse, you can place the little petunias in spring, allowing them to grow and then put them outside in June. This will encourage earlier and longer flowering throughout summer.

Ongoing care for petunias in the UK

Sunshine is vital when it comes to growing healthy petunias. Putting them in a nice sunny spot will promote multiple blooms, and will keep your garden bursting with colour during the warmer months.

Petunias also require moist soil so, during dry spells, you will want to water regularly. For petunias planted in containers watering may be needed on a daily basis to help them to thrive, but do take care not to overwater as this can result in the plants becoming leggy with far fewer flowers. Spreading ground cover varieties are very particular about water and will require weekly watering to keep them healthy.

Throughout the summer, we highly recommend feeding your petunias with liquid plant food. This will encourage maximum production of flowers that will bloom for a much longer period.

Deadheading is essential for these plants, by removing faded and dead flowers and any developing seed pods you will help to ensure a more extended flowering display. Plants that start to appear unkempt can be cut back relatively hard. You can then feed them with more liquid plant food, and this will usually encourage new growth and a fresh batch of flourishing flowers.

When the colder months hit and the frost has taken its toll, then bedding petunias should be dug up and can then be composted.

Combating pests and damaging diseases for petunias in the UK

They may look dainty, but petunias are tough cookies and can withstand a fair bit of neglect and poor weather conditions. But, as with all plants, there are a number of pests and diseases that can cause all kinds of damage.

We’ve put together a list of the most common pests and diseases and how you can tackle them to keep your petunias happy and healthy.

Caterpillars

Humans may adore petunias, but caterpillars may well be their biggest fans. These irritating creepy crawlies love to dine out on foliage and buds and, if left unchecked, can cause some fairly significant damage.

close up of a bright green caterpillar eating a plant
Caterpillars will happily munch their way through your petunias if left unchecked.

If you can face it, the best way to get rid of these beastly mini beasts is to pick them off by hand daily; you can then either release them into the wild, far from your garden or if absolutely necessary, drown them in a bucket.

If handpicking caterpillars sounds like too much of an ordeal, then weekly sprays of Bacillus thuringiensis will quickly and efficiently kill them off.

Mites

These microscopic monsters suck the juices out of the very cells of your petunias, this leads to the discolouration and hardening of flowers and can cause leaves to curl and cup.

Mites are cousins of spiders, and this means they leave telltale webs behind them as they feed. If you notice these little trails, then treat your petunias with a spray of neem oil once a week until all signs of the mites have disappeared.

Thrips

Thrips can be difficult to see, but they have a similar appearance to ants. These nasty little things can carry viruses that are harmful to petunias and cause flowers to develop white spots and leaves to appear papery and weak. Thankfully, as with mites, neem oil can be employed to rid your plants of these pesky perpetrators.

Powdery mildew

One of the most common reasons for powdery mildew to appear is plants being planted too close together. Avoiding planting to tightly to begin with will help prevent this mildew from striking.

If you do find yourself with a powdery mildew issue then, once again, neem oil applied weekly will help your petunias to become fighting fit once again.

Root, stem and crown rot

Petunias planted in areas with poor drainage will frequently fall victim to root, stem and crown rot. Even with regular watering, leaves will wilt and stems will become fragile.

Sadly, in most cases, the petunia won’t be able to be saved, and it may be better to pull them out and start again. You can try and correct the drainage problem but, if you see the damage, it probably means the problem is too far gone to be salvaged.

Botrytis blight

This nasty little disease can be identified by post and discolouration on flowers and leaves, and will eventually produce grey-brown spores. This is another disease that thrives in wet bedding conditions so the best thing you can do is quit watering for a while. You should then prune the damaged areas of the plant and clear away any fallen debris. You can dry out the bed to prevent further infestation.

Petunia perfection

Hopefully, this article has provided you with everything you need to know about growing and caring for your petunias here in the UK.

Petunias are such rewarding plants, and their endless elegance and bountiful blooms have made them one of the most popular plants on the planet. Thanks to how easy they are to grow and care for they are perfect for gardeners at any level and also provide a fantastic opportunity for children to learn about how to tend to plants. Sunshine is a crucial component so be sure to pick a sunny little spot in your garden, and your petunias will produce an abundance of glorious, beautiful blooms for you and your family to enjoy all through the summer months.

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