Petunias make for gorgeous colorful hanging baskets and decorative lawn borders, lush with varied flower heads that last all summer long. Or they should. The thing the garden centers don’t advertise is that most varieties of petunias are fairly high maintenance.
The only type of low maintenance petunias is Milliflora Petunias, which require no deadheading – removal of spent flowers. Names of this variety include the tradename Supertunia, Picabella and Petunia Fantasy.
Spreading (Wave) Petunias are another type that don’t need pinching back. Every other variety needs regular pruning, frequent watering and fertilizer to be added.
The two most commonly available types of petunias are grandiflora and multiflora. These plants do become leggy easily without the right attention.
Something to note is that petunias are full sun plants. During blooming season, they need 5-6 hours of full-sun, all round, meaning no side of the plant should be kept in the shade.
If you have petunias in a hanging basket, perhaps on your porch where the back of the planter is in the shade, an idea is to rotate it regularly, or move the basket onto a plant stand and place that somewhere in your garden where it can get full sunlight for longer.
It may not need this every day, however the more sunlight the plant gets, the fuller petunias grow.
How to Tell Which Type of Petunia You’re Growing
If you’re not sure what type of petunia you’re growing, a good tell is the size of the flowers produced when in bloom.
- Grandiflora petunias produce the largest flower heads, usually 3 to 5 inches.
- Multiflora petunias have flower heads that are roughly 2 inches.
- Milliflora petunias are 1 to 1.5 inches.
- Wave petunias are a spreading variety with flower heads a little larger than multifloras of 2 ½ to 3 inches in diameter. Wave series are faster growers.
The reason you need to know the type you’re growing is because milliflora and spreading petunias are low maintenance, and don’t need pinching back. Multifloras and grandifloras do.
How to Keep Grandiflora and Multiflora Petunias from Getting Leggy
The trick is hacking as much as you can as often as you can. You can’t be shy giving these fast growers a regular haircut.
Provided you’re feeding the plants right (see more tips in my full care guide), they will bloom all summer long with the right water feeding combined with a good balance of trimming the plants.
To Keep Grandifloras from Getting Leggy…
Water weekly, or at least every ten days, and fertilize monthly. If the plant is already leggy, you can cut it back to about half it’s size. These rebound fast, so you can cut back a fair bit and essentially start from scratch.
One of the key components of successfully growing petunias in hanging baskets is maintaining the plants hydration. The Flower Shop Network use a good test to know you’ve given the plant the right amount of water.
Pull out a small amount of soil from the basket and roll it into a ball. If you can squeeze water from it, you’ve fed it too much. If you can’t roll the soil into a ball without it blowing away, it needs to be watered. The right balance of watering is when you can roll the soil into a ball and no water releases.
This won’t work when you’ve just watered the plant, however, the next time you water your plant, take a note of how much water you feed it. Then the next day, test the soil to see if you can roll it into a ball without releasing water.
As you should be watering the plant weekly, within a few weeks, you’ll have a good baseline of the amount of water to feed your plant each week to keep it growing strong.
To Keep Multiflora Petunias from Getting Leggy…
When multiflora petunias are planted in a good area of the garden getting full sun daily, they’ll grow faster than grandiflora petunias. Because of this, it can mean the flowers yellow faster, or you’ll find the color is fading frequently.
One of the things you can do to help grow fuller petunias of this variety is to get rid of the flowers as soon the color starts to fade. If you find any yellowing flowers, pinch them off.
This will stop the plant from spending its energy producing seeds, instead channeling more energy towards blooming. The result is more color and a bushier stem in general.
It’s also worth nothing that in wetter climates, less frequent watering may be required, as overwatering can cause petunias to wilt too.
Deadheading and Pinching Back is How to Grow Fuller Petunias
Both multiflora and grandiflora petunias will produce seeds. Deadheading is the process you need to be using to get rid of those seeds early and pinch the leaves back to encourage lush stem growth instead of seed production.
The proper way to deadhead petunias is to pinch spent flowers early by pinching the stem with your thumb and forefinger (or pruners) just above the first set of healthy leaves. Leave the leaves intact, snap the stem and the plant will produce fresh flowers throughout the summer months.
With petunias, it is best to get rid of the flowers losing color to encourage the growth of new ones. The result is the plant’s energy will be used for producing thicker, bushier stems and leaves, resulting in more vibrant flower heads.
If you’ve never pinched back plants, watch this quick video showing how it’s done (properly):
Notice how there’s no gloves worn? That’s because thick gloves can get in the way of effective pruning as it’s more likely you’ll hurt the plant by pinching back too much.
This is a part some gardeners hate because of the stickiness of the leaves on petunias. If you’d rather wear gloves, wear thin ones so you pinch back the part of the plant you intend to without damaging any other part of the plant.
Rejuvenating Petunias and Keeping Critters from Eating Them
It’s not uncommon to get your petunias growing fuller, only to find them being damaged by something mysterious when the sunlight goes down.
Often with petunias, it’s in the mornings that you’ll notice there’s damage done to the plant, but nothing in sight to explain how it happened.
A number of insects will eat petunias at night. These include, aphids, mites, caterpillars (most notably the budworm) and leaf miners. Slugs can be a nuisance too.
A number of problematic pests can be controlled by Bacillus Thuringiensis (BT), however, it is advised this is only used as a last resort. Neem oil is handy for repelling mites, and insecticidal soap will repel many garden critters.
But, the best way to prevent anything nibbling on petunias anywhere in the garden is frequent deadheading, as is required anyway.
Due to the speed that petunias grow and bloom, the more often you remove spent flowers, the more likely it is that anything trying to eat at your plants will find their way into your trash instead.
The most common causes of leggy petunias are over or underwatering, a lack of fertilizer and/or inadequate pruning.
Water weekly, use a water-soluble fertilizer once monthly and deadhead your petunias every week or every other week to prevent petunias from becoming leggy and encourage bushier, fuller growth of your petunias with far more vibrancy in color.
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.