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Trailing Petunias – The Ultimate Growing Guide

How to grow long, dense and flower-packed trailing petunias in baskets and containers

Welcome to another entry in the Our Plants section of the DIY Gardening website!

Do you want to grow long trailing petunias with masses of dense colourful flowers? Are you looking to create overflowing containers or baskets like you often see at entrances to garden centres?

While petunias are prolific growers, you’ll need to follow the steps listed below if you want to take these wonderful trailing plants to the next level.

Many gardeners struggle with petunias, especially towards the end of summer and autumn when the plant can look leggy, faded and sparse with few blooms.

Let us help you grow and maintain perfect trailing petunias.

Which Type of Petunia is Best For Hanging Baskets?

There are many varieties of petunia and most can be placed into three categories:

  • Trailing.
  • Mound forming.
  • Ground covering.

It’s worth noting that some petunias that provide excellent ground coverage also trail very well and look great in baskets and window boxes.

Our recommendation for UK gardeners looking for trailing basket petunias is to choose either the Surfinia or the Wave petunia. Both of these petunias require little maintenance and grow prolifically with the potential for long, dense trails.

Trailing petunias

The Best Baskets For Trailing Petunias

We’ve tested several different hanging baskets over the years, from cheap plastic pots on flimsy chains to metal baskets with liners.

Photos of our favourite are shown below.

This 12″ basket has six side holes which are suitable for plugs of any size, there’s also enough space on the top for a further 5 petunias.

By packing 11 petunias into a 12″ basket, you’ll be well on your way to creating a wonderful display of dense, trailing petunias.

The basket is made from sturdy plastic complete with metal chains. Each side hole has a removable patch making it easy to insert plugs.

This basket was designed for drainage with holes all around the side and one in the base.

Our only gripe – it can become heavy when fully loaded with plants and a potting mix. Also, at 12 inches, you’ll need a suitable bracket so the plants aren’t too close to the wall.

Black hanging basket
Close up of empty black hanging basket

The Ideal Potting Mix For Petunias

If soils and composts are used in hanging baskets, you may encounter some issues:

  • Weight – soil is very heavy when wet and the total weight of the basket could bend or break the hook or bracket.
  • Density – soil and compacted compost material can be very dense, this can restrict the growth of the roots which makes them less efficient at nutrient uptake.
  • Water retention – a constantly waterlogged basket can result in root rot and failure of the plants.

A simple and cheap solution is to use a mixture of multi-purpose compost, a growing medium such as coconut coir (or use peat but be aware of its environmental damage) and perlite.

The compost adds nutrients and you can create your own from garden waste. The coconut coir holds moisture but drains excess water and improves aeration, which helps to promote strong root growth with excellent nutrient uptake. The perlite creates small voids and also absorbs moisture which the roots can extract later in the day as the mixture dries.

We suggest creating a mix of:

  • 10% perlite or vermiculite
  • an even mixture of 45% coconut coir and 45% multi-purpose compost

That’s it.

Compost

The Best Place in the Garden to Locate Trailing Petunias

Trailing petunias need a minimum of 6 hours of direct sunlight if you want to grow long dense trails from baskets and containers.

Consider rotating baskets if one area of your garden receives less sunlight.

Of course, you can grow them in areas with little direct sunlight but they won’t grow as prolifically.

Drainage is also important, so to avoid root rot, raise any ground-based pots or containers with pot feet.

How to Deadhead and Prune Trailing Petunias

Deadheading a plant serves two purposes:

  • to tidy up the plant and improve the appearance.
  • to prevent seed-setting plants from “going to seed”. Once an annual plant has started to produce seeds, new growth is often reduced as the plant has achieved its goal – to create offspring. This can be prevented and growth extended by deadheading and stopping the plant from producing seeds.

A quick Google search reveals dozens of authors claiming you need to deadhead trailing petunias as often as you can if you want long dense trails.

But is this really true?

There are in fact several varieties of petunias that don’t require regular deadheading; Wave and Surfinia will grow very well with only minimal deadheading and are perfect for the busy gardener.

For most other types of petunias, regular deadheading (at least weekly but ideally twice a week) is recommended.

Pro tip: When deadheading, make sure you remove the seed pod and not just the flower. 

Pruning

Pruning is one of the most important tasks but is often overlooked or done too lightly.

Every time a stem is cut, side shoots will form and these will develop into new stems.

Prune too often and you’ll have a very dense petunia plant with short trails.

Prune too little or not aggressively enough and the few stems you have will grow long and leggy with few side shoots and few flowers.

We recommend that once a week you deadhead petunias and prune back any long leggy stems, this will encourage side-shoots which will then trail. Look for stems that are weak, have few flowers or leaves and start by pruning those.

How far back should petunia be pruned?

Try to maintain a uniform shape when pruning but don’t be afraid to prune off half the growth or more if the plant is somewhat leggy and sparse.

If you think your plant is already too far gone and is extremely neglected, leggy and with few flowers, just go ahead and prune back aggressively to just below the rim of the basket or container. Always follow any aggressive pruning by regular fertilisation to boost growth.

How to prune petunia

How to Avoid “Flat Topping”

The perfect petunia hanging basket or container won’t just have long trails but also a well-rounded top section complete with blooms and plenty foliage. 

You should be able to gain 10+ inches of height by preventing “flat topping”.

If you allow all of the stems in the centre of the basket to become leggy, they will overhang the basket edge and the top of the basket will look flat and sparse.

It’s very easy to prevent this, just regularly prune the leggy stems to encourage bushy growth near the top of the basket or container.

If you’ve neglected a trailing petunia, just go ahead and aggressively prune away so there’s around 12 inches of the plant overhanging the edge of the basket. It won’t take long for the plant to grow and much of it will be in the top section.

How Often Should Trailing Petunias be Watered?

Probably more than you think!

Here’s our watering regimen for our petunia baskets and containers:

  • Cloudy, overcast, cool, dull summer days – water every two days.
  • Typical summer day – water every day.
  • Very hot summer days – water twice a day.

Petunias require a lot of water but the roots prefer moist yet never waterlogged soil. The baskets/containers should also allow the water to freely out of the bottom.

If you water the basket and it immediately drains out of the bottom, chances are the soil is too dry and has shrunk, the water is just escaping through the gaps. To remedy this, water the plant and leave for 15 minutes so the soil expands, then water again. Moving forward; try to prevent the soil from becoming so dry that it shrinks.

Can you overwater petunias? Yes, and root rot is possible but it’s generally only a problem if your container or basket doesn’t have drainage holes or your potting mixture is so dense that the water can’t drain out. See our preferred potting mix and baskets at the top of this page.

Should you water the petunias even if it’s been raining? We usually water our petunias heavily and it’s unlikely that a light summer shower would suffice. So even after rain, we still go ahead and water them. Baskets and containers are often very small and catch a tiny amount of rain, many are located under the roof overhang which protects them from much of the rain anyway.

Fertiliser and Feed

Ask any gardener how often they fertilise their petunias and you’ll get a different answer every time. There is no set timetable but as a general rule of the thumb, nutrients that are flushed out of hanging baskets by watering need to be replaced.

Unfortunately, it is possible to over fertilise plants, even those in hanging baskets. Too much zinc, manganese, copper or phosphorous can block the uptake of iron leading to yellow leaves and stunted growth.

So how often should trailing petunias in baskets be fertilised?

We recommend fertilising the petunias in baskets after every week. So in the summer when you’re watering once per day that will be every seventh watering.

During cooler weeks, you can reduce the frequency to about once every ten days as you won’t be watering so much and the existing nutrients won’t be flushed out of the basket so often.

Of course, you can still get good results with fortnightly fertilisation but for optimal growth, we think you should apply a little more frequently.

As for petunias grown in the ground or flowerbeds, you won’t need to fertilize so often. Neither do petunias grown in large containers need such frequent fertilisation. 

Do remember that baskets often dry out very quickly in the summer and therefore need more watering.  The more water that is used, the more fertiliser that is required to replace the lost nutrients.

Also, keep an eye out for signs of over fertilisation, such as yellow petunia leaves. If that happens, dial it back and feed the petunias some sequestered iron.

Best Fertiliser For Petunias

We suggest starting with a good all-rounder such as Miracle-Gro soluble universal fertiliser which has a high concentration of nitrogen which is perfect for encouraging long trails.

As the season goes on, you can swap the occasional feed with a fertiliser with a higher ratio of Phosphorus if you find the petunias are somewhat leggy and producing small or few blooms.

We also recommend feeding the petunias a monthly dose of sequestered iron to keep the leaves nice and green.

We’ve used this product and had great results getting the petunia foilage back to a lush green colour.

Miracle grow

Fertiliser Alternatives

Are there any alternatives to fertilisers?

If you don’t want to use chemical fertilisers, you have a couple of options; use seaweed extract organic fertiliser or pot up your plants throughout the growing season.

Potting up hanging baskets is a little tricky but is a great way to feed your plants without using any fertiliser.

Let’s say you start with 6″ hanging baskets, after a couple of months you can move the plants to 9″ baskets and fill the extra space with organic matter such as compost and manure. Towards the end of summer, you could then migrate the plants to a 12″ basket and top up with more organic material.

Seaweed extract is also a safe way to feed plants so do check the reviews of this product:

seaweed extract

Are You Aggressively Fertilising Your Petunias?

Watch out for two things:

  • High pH levels – petunias thrive in pH levels between 5 and 6 and may suffer yellowing and stunted growth if grown in soil near and above 7. Not sure of your soil’s pH level? Try one of these soil testing kits, they’re cheaper than you think.
  • Excess minerals may block or reduce the uptake of iron, leading to yellowing (interveinal chlorosis). Reduce the amount or frequency of fertilisation and feed monthly with sequestered iron to resolve.

Top Ten Tips (A Summary)

Here are our top ten tips for growing trailing petunias, we’ve kept each one short and to the point:

 1) Research

Research the type of petunias you are growing, not all of them trail well and some require deadheading while others don’t.

 2) Sunny Spot

Trailing petunias will perform best in a very sunny spot, ideally with at least 6 hours of sunshine per summer day. Avoid shaded areas of the garden.

 3) Water

Petunias need lots of water, probably more than you think. Aim for once a day watering in the summer, double that when it’s very hot.

 4) Feeding

Petunias in hanging baskets need more fertiliser than plants in flowerbeds. The more you water the basket, the more nutrients you’ll need to replace.

 5) Companion Plants

Choose companion plants that can cope with lots of frequent watering and fertilisation. Other annuals such as pansies and geraniums are popular.

 6) Deadheading

Don’t forget to deadhead your flowers to improve the appearance, for many petunias it will also encourage new growth and blooms, even into autumn.

 7) Planting

Plant appropriately as petunias can spread far if in borders and baskets and will develop long trails in placed in baskets and watered/fed frequently.

 8) Potting Mix

Choose a potting mix with lots of aeration, perlite and other moisture-retaining materials. Avoid heavy and dense soils that restrict root growth.

 9) Basket Size

For really long and dense trails, use a basket that’s large and has side holes for extra plants. Watch out, you might need a strong bracket or hook.

 10) Pruning

Pruning will stop petunias from growing long and leggy later in the season and will encourage new bushy growth with fresh foliage and blooms.

Below is a selection of products we recommend:

 Ergonomic Secateurs

These lightweight secateurs are razor-sharp so are ideal for trimming back petunia stems and deadheading – something you’ll be doing a lot of with this plant!

 Hanging Baskets

We love these hanging baskets for their size, sturdiness and also the extra side holes – perfect for filling with lots of long-trailing petunias.

Black hanging basket

 Coconut Coir

Petunias grow well in coconut coir with compost, perlite & optionally vermiculite which all improve drainage, aeration & moisture control.

Coconut coir

 Organic Fertiliser

Want to go green… literally? Try these slow-release organic fertiliser pellets from Miracle-Gro. Safer for the environment and you.

Fertiliser pellets

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This guide to growing trailing petunias was created by the team here at DIY Gardening

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