Petunias 101: How to Grow Petunias From Seed the Easy Way

Petunias 101 How to Grow Petunias From Seed the Easy Way

It’s easy to see why Petunias are one of the most popular plants in gardens the world over. They produce stunning flowers in almost every colour of the rainbow, remain in bloom from spring to autumn, and their diverse growth habits make them versatile plants for pots, beds, borders, and baskets. 

But despite their beauty and longevity, Petunias have earned themselves a reputation for being somewhat tricky to grow from seed. In fact, this couldn’t be further from the truth. Petunias will germinate prolifically so long as their specific yet simple needs are met, and growing from seed is by far the best, most cost-effective, and most rewarding way for you to fill your garden with an abundance of colour this year. 

This guide to growing Petunias will teach you all you need to know to nurture your own Petunias from a packet of seeds to plentiful blooms. 

What Are Petunias

What are petunias

Petunias comprise a sizeable genus of flowering tender perennials which originate from South America. Belonging to the Nightshade family Solanaceae, Petunias are related to tobacco, chilli, and deadly nightshade. They vary in height from around six inches to eighteen inches tall, and depending on the variety, they can spread up to four feet. Petunias can be both single or double-flowered and are mostly smooth trumpet or flute-shaped, although some varieties have ruffled edges and a rose-like appearance. 

History of Petunias

History of Petunias

Petunias were first discovered in the 16th century by Spanish explorers in the Americas. They were known by the native Tupi-Guarani peoples as petun, which translates to ‘worthless tobacco plant’, and were perceived at the time as being ugly.

It wasn’t until the 19th century that the Scottish botanist John James Tweedy rediscovered the species on a trip to South America and brought samples back to the Glasgow Botanical Gardens, that Petunias were first introduced to Europe. Botanists soon began experimenting with hybridisations of Petunias to develop larger, more colourful, and more ornate, double-flowered varieties, which is how we came to have the wonderful array of varieties that we do today. 

What Do Petunias Symbolise

What do Petunias symbolise

Petunias have been ascribed many different meanings by different communities and civilisations throughout history. 

The Maya and Inca people believed that the strong scent given off by Petunias helped to ward off evil spirits from the underworld. They used the petals to make protective potions. 

In New Age spiritualism, it is thought that Petunias won’t grow in places where there is negative energy, so the presence of Petunias indicates a positive space. 

Petunias haven’t always been associated with the bright, cheerful meanings that think of today, during the 1500s, they were thought to be a symbol of demonic power and signified resentment and anger towards the recipient when given as a (somewhat unwelcome) gift. 

Types of Petunia

Types of Petunia

Petunias are generally differentiated into five main groups, depending on their flower size. Let’s take a look at some of the best varieties of each group for you to grow from seed.  

Multiflora Petunias, as their name suggests, bloom prolifically, offering a dazzling display of small but abundant flowers. They are fairly hardy and can tolerate more moisture than other varieties, so are best suited to beds and borders, where the soil tends to retain more water. They are also the sturdiest variety, with strong stems that allow them to withstand gusty winds.  

Best Multiflora Varieties to grow:

Carpet is a popular Multiflora variety that produces fluted blooms in reds, whites, yellows, or purples, and provides excellent ground cover. 

Heavenly Blue produces plenty of vibrant indigo-hued flowers with a spreading growth habit that looks great in borders or baskets. 

Primetime are instantly recognisable for their trumpet-shaped, rich-coloured petals with striking white stripes in the centre. They have a compact growth habit making them perfect for pots. 

Grandiflora Petunias have the largest flowers of all varieties, although they flower less abundantly than Multiflora varieties. Their flowers are usually between three and five inches across, so really stand out against the foliage. Grandiflora don’t tolerate excess moisture well, so are best suited to pots and baskets which dry out quicker than borders and beds. 

Best Grandiflora varieties to grow:

Rose Star has uniform, bright, fuchsia-coloured petals with a distinctive white star shape in the centre. Their compact and upright growth habit is perfect for pots and containers. 

Storm Petunia has vivid lavender-coloured, single-flowered blooms which grow to around ten centimetres in diameter. This cultivar has been bred to withstand wetter climates more successfully than most Grandiflora varieties, so if you live in a rainy location, Storm is the Grandiflora for you! 

Sugar Daddy  Petunias have deep purple-hued petals often decorated with ornate vein-like patterns. They are one of the most popular Grandiflora varieties, giving off a subtle vanilla scent to entice humans and pollinators alike. 

Milliflora Petunias produce the smallest flowers of all Petunia varieties, although they often remain in bloom for the longest. Their flowers are usually around an inch in diameter, and their compact growth habit makes them ideal for dense planting. 

Best Milliflora varieties to grow:

Best Milliflora varieties to grow

Fantasy is a popular Milliflora variety with a compact growth habit and petite, delicate flowers ranging in colour from white to blue to purple to deep reds. 

Shock Wave will produce flowers from early spring onwards, even in colder climates. They are fairly weather-resistant and can withstand rainy climates better than most Petunias. 

Picobella is a pretty dwarf variety that produces plenty of elegant flute-shaped flowers. Their mounded growth habit makes them perfect for pots and containers. 

Trailing Petunias, sometimes called ‘Wave’ or ‘Spreading’ Petunias, are low-growing varieties with a wide spread. They offer colourful ground cover in beds and borders but are equally well suited to hanging baskets where they will elegantly cascade downwards. They tend to grow vigorously but may need deadheading in midsummer. Trailing Petunias are more drought-tolerant so are perfect for hotter climates. 

Best Trailing varieties to grow:

Hang Out is a vibrant, single-flowered variety available in indigos, pinks, and whites. Its vigorous cascading growth habit makes it perfect for hanging baskets. 

Purple Wave was the very first trailing Petunia cultivar. It produces an abundant display of deep magenta and plum-coloured flowers which look great in hanging baskets. 

Priscilla are a stunning double flowering variety, displaying lilac-coloured petals adorned with deep purple vein-like patterns. They give off a stunning scent during the evening. 

Floribunda Petunias are an amalgamation of other varieties. They have been bred to exhibit the best qualities of each of the main groups of Petunia, so are fairly hardy and water-tolerant. They produce many medium-sized blooms and have a somewhat trailing growth habit. Floribunda varieties tend to be ‘self-cleaning’, meaning their flowers drop naturally once they die, so there’s no need to deadhead them. This variety is perfect if you are looking for a low-maintenance Petunia. 

Best Floribunda varieties to grow: 

Celebrity is a hardy, rain-tolerant variety which is perfect if your garden is in a wetter climate. Unlike most Petunias, it can also tolerate semi-shade conditions and produces beautiful lavender, rose, white, or yellow coloured flowers. 

Double Madness produces some of the most show-stopping blooms of all Petunias, with intricate double flowers in an array of pink and purple hues. 

Merlin are some of the hardiest and lowest-maintenance Petunias. They have a compact growth habit which is ideal for dense planting and are available in a variety of colours to suit any planting scheme. 

How to Grow Petunia From Seed

How to grow Petunia from seed

Although you can often buy Petunias as young plugs or mature plants, the best, and most cost-effective way to grow them is from seed, especially if you have a large space that you want to fill. If you do opt to buy Petunias as plugs, select short, compact, and dense plants, as these will produce the most blooms, but avoid overly tall or spindly plants.  

Petunias seeds need to be started off indoors at least eight to ten weeks before the last frost has passed. You should start the seeds off in a seed tray filled with seedling compost. Petunia seeds are tiny, almost dust-like, so it can be tricky to distribute them evenly across your soil. Once sown, don’t cover the seeds with soil, as they won’t germinate if they don’t receive enough light. Give the seeds a light misting with a spray bottle and cover the seed tray with a clear plastic lid or plastic wrap to help retain warmth. The seeds should be kept away from direct sunlight at temperatures above 24°C to activate germination, and the temperature should be kept consistent during day and night. Germination usually takes around 14 days. 

Once the seedlings begin to emerge from the soil, you can remove the plastic covering and place the seed tray in a cooler spot (around 18°C), where they will receive plenty of direct light. A south-facing windowsill is a good option, or underneath fluorescent or LED lights if you have them. The lights should be positioned six inches above the top of the plants. During this stage, you should allow the soil to dry out completely between waterings. Overwatering will cause the seedlings to rot. 

Once the seedlings have developed at least two true leaves they can be gently pricked out and transferred into individual pots filled with moist, well-draining soil. Continue to provide plenty of direct light until they are ready for hardening off.

Once the last frost has passed, you can begin hardening off your Petunia seedlings to acclimatise them to outdoor conditions. Place the seedlings outside for a few hours each day, leaving them out for incrementally longer periods over the course of a week or two. Once acclimatised, your seedlings will be ready to plant out in their final position. Fertilising your Petunias as soon as you plant them out will give them a head start for abundant blooms. 

Where to Plant Petunias

Where to plant Petunias

If you are planting your Petunias in beds for ground cover, they should be spaced around one foot apart, although this is flexible depending on the variety. In pots, the seedlings can be placed closer together to produce a more dense display, especially if using a variety with a compact or upright growth habit. Choose a full sun position with well-draining soil. Petunias can be fragile, so try to select a position where they will be protected from strong winds. 

Caring For Petunias

Caring For Petunias

Temperature and Humidity 

Petunias love heat! They do best when daytime temperatures are between 15 and 26°C. If you live in a very warm area, you may need to provide some shade to protect them from the sun’s hottest rays during the afternoon. Prolonged periods of extreme heat can sometimes cause flowers to become stunted temporarily. Petunias are not humidity lovers and prefer a place with warm, dry air and good circulation. 

Light

Petunias need a least six hours of sunlight per day to thrive and produce their stunning flowers. The more sunlight they receive, the more flowers they will produce. They tend to become spindly when they don’t receive enough direct sunlight and will struggle to produce any flowers at all in full shade. 

Soil

Petunias are generally moisture-averse, so need loose, well-draining soil which won’t become waterlogged. They like a fertile substrate, so work plenty of organic matter into borders before planting, or use an enriched potting mix for containers. Adding organic matter and compost to borders will also help to improve drainage. Petunias are not overly fussy about pH levels, but you will find they produce their most prolific blooms in slightly acidic soil. 

Water

In most locations, weekly watering throughout the growing season should suffice. If you chose to grow your Petunias in hanging baskets, you will find they dry out more quickly and will need a slightly increased watering schedule. When watering your Petunias, take care to water the soil rather than the foliage, as the sun can scorch the leaves if they get wet. Overwatering can cause root-rot or spindly growth, but they aren’t drought-tolerant, so will need to be watered more regularly during very hot dry spells. 

Food

Petunias grow most vigorously during springtime, so this is the period when they will need the most food. You should aim to feed your Petunias at least monthly, if not fortnightly, with a well-balanced or high-potash fertiliser to maximise their blooms. Continue feeding throughout the summer and into autumn to ensure longevity. Most species of Petunia will bloom from spring right through to the first frost if they are fed regularly. More ornate, double-flowered varieties tend to be hungrier than single-flowered varieties. 

Pruning

Pruning

Pruning your Petunias will help to maintain their beautiful blooms long into late summer and autumn. Often, petunias become ‘leggy’ or spindly during midsummer, so cut the long, leafless shoots back by about half to encourage dense new growth. Fertilising immediately after pruning will promote faster regrowth. Faded or dying flowers should be deadheaded periodically throughout summer to get rid of any seed heads which compete with the flowers for energy. 

Winter 

Petunias are a tender perennial, although they do not tolerate frost so should be treated as an annual in most climates. Frost will kill your petunias, so they will need to be dug up and disposed of in the compost bin after the first frost of the year has arrived. 

If you really want to preserve your Petunias for next year, you can prune them right back and lift them just before the first frost arrives. Place them in pots with fresh compost, and put them in a cool, dry place indoors. Water the plants thoroughly at first, and gradually reduce watering and light levels over the next few weeks to allow them to dry out and become dormant. Don’t worry if the leaves begin to drop, this is normal in dormancy. As we enter spring, you can slowly increase the watering frequency and light levels to break the dormancy. Once the last frost has passed, you can harden them off before planting them back outside. 

Pests and Disease 

One of the reasons Petunias are so popular is that they are relatively pest and disease resistant, but you should still keep an eye out for any symptoms of common garden pests. 

Aphids are a common pest that suck the sap from the plants’ tissue. If infested, the foliage will become yellowed and wilted, and the flowers can become misshapen. Happily, aphids are fairly easy to treat using insecticidal soap, and sometimes a steady stream of water from the hose will be enough to dislodge aphids. Their populations are easily kept under control by their natural predators like lacewings and ladybirds. 

If you notice holes or ragged edges on your Petunias’ foliage, it’s probably due to slugs or snails munching on the leaves. You can discourage them from feeding on your Petunias by planting strong-smelling plants like garlic or chive nearby, as the pests are averse to these aromas. You could also place beer traps near your Petunias to drown the slugs. 

The most common disease affecting Petunias is root rot, caused by overwatering or by being planted in dense soil which retains too much moisture. The symptoms of root rot are wilting foliage and mushy stems. Unfortunately, once root-rot has set in, the plant is often unsalvageable. If you live in a very rainy climate, opt for a more moisture-tolerant Petunia variety to avoid root-rot. 

FAQs

FAQs

What do Petunias smell like?

Many Petunia varieties will release a sweet-smelling scent at dusk to attract moths and other evening pollinators. Some also give off their fragrance during the day, but it is usually stronger at night.

Are Petunias hard to care for?

Provided that they receive the right amount of sunlight, Petunias are very easy to care for since they don’t require a meticulous watering schedule and are fairly drought tolerant. 

Can Petunias be grown indoors? 

Whilst Petunias will surely be happiest outdoors in full sun, it is possible to grow them indoors on a sunny windowsill. 

Wrap Up

Wrap Up

Petunias are some of the most productive, rewarding, and cost-effective plants to grow from seed. With so many colours, sizes, and growth habits to choose from, these low-maintenance, high-impact, long-lasting plants are sure to bring plenty of cheer to any outdoor space, no matter how big or small, so what are you waiting for? Get sowing!

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