Trailing Petunias – The Ultimate Growing Guide

Are you looking to grow trailing petunias with long trails and hundreds of blooms?

I’ve been growing petunias for nearly a decade, and they’ve become a mainstay of my summer baskets.

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.

I’ve seen 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 me 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.

Based on my experience, I recommend UK gardeners 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.

The Best Baskets For Trailing Petunias

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

Photos of my 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, I was able to create 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 and I found it very easy to insert plugs.

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

I have only one gripe – it became very heavy when fully loaded with plants and a potting mix. Also, at 12 inches, I had need buy a wider wall bracket, so the plants weren’t too close to the wall.

The Ideal Potting Mix For Petunias

If heavy 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.

I’ve found that a mixture of multi-purpose compost, coconut coir and perlite is best:

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. 

The perlite creates small voids and absorbs moisture that the roots can extract later in the day as the mixture dries.

I’ve had good results by mixing:

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

That’s it.

The Best Place in the Garden to Locate Trailing Petunias

I’ve tried growing petunias in shade before and the results weren’t great, I was rewarded with plenty of foliage and few flowers.

Based on my experience and testing I feel that trailing petunias need a minimum of 6 hours of direct sunlight and if you can provide them more, do so.

Drainage is also important as petunias hate wet feet, so to avoid root rot, I suggest raising 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; I’ve grown both wave and Surfinia and they both performed well with only light pruning.

For most other types of petunias, I’ve found that regular deadheading (at least weekly but ideally twice a week) is best.

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 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 of foliage. 

I’ve been 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.

I’ve found it very easy to prevent this: I just prune the leggy stems once every week or so in the summer 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. Petunias are very fast-growing plants and I’ve seen them recover quickly from aggressive pruning like this.

How Often Should Trailing Petunias be Watered?

Probably more than you think!

Here’s my watering regimen for my petunia baskets and containers that I keep in full sun:

• Cloudy, overcast, cool, dull summer days – water every two to four days.
• Typical summer day – water every day or every two days.
• Very very hot summer days – water morning and evening.

In my garden, the 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 like this.

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? I usually water my petunias heavily as it’s unlikely that a light summer shower would suffice. Baskets and containers are often very small and catch a tiny amount of rain and many are located under the roof overhang, which protects them from much of the rain anyway.

If your basket or container has only one or two drainage holes, you’ll need to be careful not to waterlog the roots, which could kill the plant.

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?

I recommend fertilising the petunias in baskets after every two weeks. So in the summer when you’re watering once per day that will be every 14th watering.

During cooler weeks, you can reduce the frequency to about once a month 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 monthly fertilisation but for optimal growth, I 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 feeding.

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

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

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

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

Fertiliser Alternatives

Are there any alternatives to fertilisers?

If you don’t want to use regular fertilisers, try seaweed extract organic fertiliser.

I tested seaweed extract back in 2018 by using it on all my annual plants for an entire year and I had great results:

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.

Inspiration and Ideas

From garden edging & fast-growing shrubs to hedges for privacy & garden plants that produce beautiful winter colour. Explore our ideas & inspiration corner. Start here