When to plant petunias

Caring For Petunias: How To Grow Petunias

Growing petunias can offer long term color in the summer landscape and brighten dreary borders with lovely pastel colors. Proper petunia care is simple and easy. After learning how to plant petunias you can include them in your flower bed and container garden.

Four species of petunias include hundreds of cultivars and offer a perfect addition to the home landscape:

  • Grandiflora petunias is the most common type of growing petunias. This species features 3 to 4 inch blooms which often grow upright, but may spill over the side of your container or window box.
  • Multiflora petunias have smaller flowers and a more abundant bloom.
  • Milliflora petunias are miniature versions of growing petunias, compact and reblooming.
  • Spreading petunias are only 6 inches tall and can rapidly cover a selected area to function as a blooming ground cover.

Care of Petunias

Care of petunias includes regular watering and as much sunlight as possible to promote multiple blooms. Spreading ground cover petunias are pickiest about water, weekly waterings should be included in the care of petunias.

While petunias will grow in a partially shaded location, a fuller and more abundant bloom is produced in full sun. Soil prepared before planting petunias should have well-composted organic matter worked in.

Care of petunias will include regular fertilization with a balanced, water soluble fertilizer designed for blooming plants. As they are heavy feeders, petunias care will also include weekly feedings. Proper light, water and fertilization when caring for petunias will ensure a long season of beautiful blooms.

Proper petunia care involves removing spent blooms and the seeds they may produce. When deadheading the growing petunias, remove the base of the flower to include seed removal. Petunias allowed to go to seed will slow or stop blooming.

Purchasing Petunia Plants

Hundreds of cultivars of petunias are available to the gardener for use in a range of garden designs. Double and single blooms offer a selection of solid and multi colored flowers.

When purchasing young petunias, choose plants with a compact form and unopened buds. Open blooms on the petunia are best removed after planting for a more abundant show in the future.

Growing petunias is easy and rewarding. As you learn how to grow and plant petunias, you will never be at a loss for a beautiful bloom for a full sun area.

One thing I love about the warmer months of the year is the flowers in bloom. They are gorgeous.

But one thing about ‘the gardening bug’ is that it doesn’t always come with an instant green thumb. If this is you, meaning you love flowers but struggle to grow them, I want to inform you of a wonderful option to try: petunias.

I’ve grown petunias for years. They’re simple to grow and gorgeous to look at. Here is all you need to know to grow petunias successfully year after year:

Petunia Varieties

Petunias are annuals in most locations. If you live in planting zones nine through eleven, you could potentially grow them as perennials.

Either way, your petunia varieties fall into two categories:

  • Grandiflora
  • Multiflora

Grandiflora varieties have larger flowers. These are great to go in hanging baskets or containers because of how big they are and their ability to flow.

Multiflora varieties produce smaller flowers, though they come in thicker. These are a good option for flower beds because they handle wet weather better than the other variety.

Starting Petunias from Seed

Petunias are easy flowers to grow once they’re transplanted. It is recommended to purchase petunias from a local nursery and transplant them. This should help you find success when growing them.

However, if you prefer to start petunias from seed and grow them yourself be advised they can be tricky. Here is how you grow petunias from seed:

1. Start Early

Petunias need to be started from seed around 10-12 weeks before you want to plant them outdoors. You should wait until after the last spring frost to move them outdoors.

Knowing your frost dates can help you decide when to start your seeds indoors.

2. Give Them Plenty of Light

Place your seeds in grow cells. Be careful to sprinkle the seeds on top of the dirt, but don’t cover them up.

From here, be sure to place the trays under a grow light to give them ample amount of sunlight. If you cover the seeds you’ll block the sunlight and could hinder germination.

Petunia seeds need warmth and light. You could place the trays on top of a seed starting mat to help them germinate quicker.

Depending upon the heat and light given, it could take the seeds anywhere from five to fifteen days to germinate.

3. Water Accordingly

When starting your petunia seeds, you should place a tray of water beneath the seed starting tray. This allows the seeds to absorb water from the bottom of the tray without being disturbed.

4. Count to Three

Finally, when you see three leaves on each seedling, you’ll know it’s time to move your petunias outdoors.

Planting Petunias Outdoors

When you’ve moved your seedlings outdoors or purchased your transplants, you should be sure it’s after your last spring frost.

Also, you’ll need to make sure the area you’re planting the petunias in has fluffy, well-drained soil; is in full sun (or at least partial sun); and has a soil pH of 6.0-7.0.

Next, be sure to dig a six to eight-inch hole for your petunias to be planted in. Each flower will need its own planting hole.

Keep in mind, it’s recommended to plant petunias 12 inches apart if they’re going in a bed and 10 inches apart if they’re going in a container. Be sure to add organic matter to each hole to give the petunias their necessary nutrients from the start.

Finally, you’ll place the flower into the hole, put the dirt around the base of the flower, and push down gently. From there, water the plants thoroughly.

How to Care for Petunias

Petunias are easy plants to grow. They don’t require much care, but the few things they do need from the gardener are important. Here is what you need to know:

1. Water Matters

Like any living thing, petunias need water to survive. If you plant petunias in a bed, and you aren’t in the midst of a drought, you should be able to get by with watering them one time per week because they’re heat tolerant.

However, if you plant petunias in containers they’ll need to be watered almost daily. Their shallow root systems make it difficult for them to obtain the necessary moisture when placed in environments with limited soil.

2. Fertilizing is Necessary

Petunias like to be fed regularly. It’s recommended to feed them with a water-soluble fertilizer on a bi-weekly to monthly basis.

Many times we give too much fertilizer, making our plants spindly or having great foliage but poor fruit. There will be a time each growing season where the blooms of a petunia weaken, and they turn spindly anyway. I’ll share with you how to handle this a little further down in this post.

3. Deadheading is Your Friend

Petunias will produce blooms, and they’ll begin to fade at a certain point. When this begins to happen, you need to deadhead.

Deadheading is the process where you pinch off old blooms to make room for new blooms to come out and give the flower a fresh look.

4. Mulch Helps

It’s a good idea to place a two to three-inch layer of mulch around the base of petunias. You can apply this to plants growing in containers or those growing in flower beds.

Mulching will help suppress weeds and keep soil moist and cool which helps the plants to thrive.

5. Give Petunias a Trim

Petunias will produce from spring to mid-fall. Around mid-summer, the plants will begin to get exhausted. You’ll notice the stems becoming spindly and the flowers fading.

When this occurs, cut the stem back to half of its original size. This allows the plant to regrow and produce healthier stems and flowers for the remainder of their growing period.

6. Sunlight Can Make a Difference

Petunias can grow in full sunlight or partial shade. Keep in mind, if you grow your petunias in partial shade they may not produce as many flowers as they would in full sunlight.

If your plants aren’t producing, look at where they’re located to see if lack of sunlight could have something to do with it.

Problems with Petunias

Petunias have very few problems. This is what makes them ideal for those who have a difficult time gardening, or those who are new to gardening. Here is what you should look out for when growing petunias:

1. Aphids

Aphids are tiny bugs which can be found in most gardens. They suck juices from the stems and leaves of plants.

When you spot these pests on your plants, either use an insecticide or spray the plant with cold water. Finally, remove any damaged part of the plant.

2. Caterpillars

It’s very common to see caterpillars hanging out around your plants. They like to munch on them. You should handpick them from the plant and remove any damaged part of the plant.

3. Gray Mold and Bacterial Soft Rot

Both of these diseases will form on your petunias if they are in areas with too much moisture. You’ll begin seeing your plants becoming soft and discolored. You should choose varieties which are resistant to moist weather.

4. Viruses

Petunias are prone to different viruses such as mosaic virus. You’ll recognize signs of a virus because the plants will become discolored and begin to wilt. When this happens, you should clean any tool which has come in contact with an infected plant to stop from spreading the virus.

Also, any plants showing sign of infection from a virus should be immediately removed and discarded. Be sure you don’t compost these plants as the virus could spread throughout the compost and infect any area it’s applied to.

5. Wild Life

Animals such as deer and rabbits could potentially make a snack out of your petunias. There are multiple ways to deter deer from hanging out in your yard.

If you have rabbits in your yard, it’s a good idea to keep your dog or cat outside for a few days as a deterrent.

Best and Worst Companion Plants

Every plant has certain plants they grow better around and other plants they don’t grow well with. When looking for good companion plants for petunias you should consider other flowers who have similar water and sunlight requirements.

Good companion plants for petunias are:

  • Geraniums
  • Marigolds
  • Zinnias
  • Lavender

Each of these plants enjoys full sunlight and have similar water requirements as petunias do.

However, you should avoid planting petunias with cacti as they have drastically different water requirements.

How to Save Petunia Seeds

You should allow petunias to grow until they are finished producing. They aren’t the type of plant you would cut for indoor flower arrangements.

However, you can harvest their seeds to grow them for free year after year. Here is what you need to do to harvest petunia seeds:

1. Stop Deadheading

When you’re ready to begin saving seeds for the next season, you should stop the deadheading process. You should wait until early fall to begin this process.

2. Look for the Seed Pod

After you’ve begun letting flowers live out their life, fade, and die, you should begin to look for a seed pod. This is under the old bloom at the base of the flower. The scientific term for its location is the calyx.

When the flower begins to die, let it do this naturally. Don’t remove the flowers to speed up the process of getting to the seed pod.

After the last bloom has fallen, let the seed pod dry until you begin to see it crack. Check the seed pod daily.

When it’s cracked, remove it from the plant by cutting it off.

3. Dry Your Seeds

You should bring your seed pod indoors to finish drying. You’ll crack the pod open and remove smaller petunia seeds from the pod.

4. Crack Them Open and Store

When the pod has been cracked open and the seeds removed, place the seeds in an envelope. Store them in a cool, dry location until you’re ready to start new petunias the next season.

Well, you now know how to start your own petunias from seeds, how to grow them, care for them, protect them from pests and diseases, who to plant them with and who to avoid, and how to harvest your own petunia seeds.

Now, I want to hear from you. Do you have any secrets for growing petunias? Do you have a particular flower you love to grow every year?

We’d love to hear from you. Leave us your thoughts in the comment section below.

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Plant petunias now through mid-October

News Release Distributed 09/20/12

By Allen Owings, LSU AgCenter horticulturist

Petunias are one of the most popular flowers in Louisiana. They can be planted in fall for cool-season color or planted in late winter or early spring for warm-season color. As with almost all bedding plants these days, you can find a wide assortment of petunias at local garden centers.

For best results, plant petunias in September through early November or late January through mid-March. Petunias do better during winter in south Louisiana. Their performance depends significantly on how cold a winter we have.

Many flower colors are available in petunias. You can find single-flowered petunias and double-flowered petunias. Normally, the single-flower forms are more reliable than the double-flower forms in the long term.

Some “best management practices” to provide enjoyment from your petunias from now through late spring include:

– Properly prepare the landscape bed to allow for good internal drainage and aeration.

– Add fresh, nutrient-rich, finished compost to landscape beds to provide nutrients.

– For a traditional fertilizer approach, apply a slow-release fertilizer at planting.

– Make sure landscape beds have a soil pH between 5.5-6.0.

– Select a full-sun location in the landscape. If you want petunias to extend longer into the summer, plant in a partially shaded location but realize flowering will be less.

– Complete late winter or early spring petunia planting by mid-March.

– Use irrigation only when needed. Over-watering leads to root rot and stem dieback problems.

– Be aggressive and plant in masses for the best visual enhancement.

– For performance longer into the late spring months, lightly deadhead after the first peak bloom.

Great petunia varieties include the Wave, Easy Wave, Tidal Wave, Shock Wave, Madness, Dreams and Supertunias. Petunias are popular bedding plants and are not difficult to grow. Just follow these recommendations and select nice, vigorous, healthy plants to get you started.

You can see more about work being done in landscape horticulture by viewing the LSU AgCenter Hammond Research Station website. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals.

Rick Bogren

All About Petunias

Petunias have always offered nonstop summer bloom, but now you’re more likely to find a color, size, and growth habit to suit your garden needs. New, vigorous trailing types and miniature-flowered types have rekindled gardeners’ interest.

Petunias are low-growing, bushy to spreading tender perennials usually grown as annuals. Their soft, thick leaves are slightly sticky to the touch. Trumpet-shaped flowers have a single set of plain-edged petals, or can be doubled, ruffled, or fringed and come in colors from light pink through dark red, and pale blue through deep purple. You’ll also find white, cream, and even a new bright yellow. Many flowers have veins of accenting colors, or alternating stripes.

Plants grow in all climates, preferring the warmth of summer; most die at or just below freezing. Gardeners in mild-winter climates know petunias as winter annuals or even short-lived perennials.

Kinds of petunias

Most modern petunias descend from two wild species from Argentina, a large white one (P. axillaris) and a violet-flowered one (P. integrifolia, formerly P. violacea). The initial hybrids of these two were produced in Germany and England in the early 1800s. Over time, they proved so stable–not to mention popular–that botanists now refer to them simply as P. hybrida.

This nearly 200 years of gene mixing combined with petunias’ great popularity (and the modern habit of giving plants a trademarked name) has led to some confusion among types.

When planning a petunia color scheme, keep in mind that purple-flowered varieties tend to be the most vigorous, while yellow ones–except for ‘Prism Sunshine’–are the least. Red-flowered varieties of all types also tend to be weak. The breeding required to produce yellow and red varieties results in genetically weaker plants than the naturally hardy purple ones.

Following are descriptions of the basic petunia hybrids, with listings of strains that I’ve found to be superior.

Grandiflora. Of all petunias, these produce the fewest but largest flowers, 3 to 5 inches across. Since their introduction in the 1930s, they’ve been the most popular type of petunia.

Plants grow 1 to 2 feet high and 2 to 3 feet wide. The flowers can be single, ruffled, or fringed. Colors include blue, pink, red, rose, salmon, scarlet, white, and pale yellow, plus striped forms of these colors. Double flowers are also available.

Grandifloras are damaged by rain and strong winds. Also, the plants’ thick, heavy stems have a tendency to fall over, resulting in unsightly holes in the planting. It may be difficult to find a place in the garden protected enough to show off grandifloras’ full splendor all season. I like to grow them in a cutting bed and let the flowers take a starring role in arrangements.

Among the grandifloras, the big news is ‘Prism Sunshine’. This 1998 All-America winner is notable for both its bright yellow color and its vigorous growth. (Earlier yellow petunias produced weak plants of modest performance.)

Multiflora. Sometimes called floribundas, multiflora plants are similar in size to grandifloras, but their flowers are only about 2 inches in diameter. Their chief virtue is more abundant flowers that have greater resistance to disease and bad weather. Because their branching is denser, they are less likely than grandifloras to flop over. They are also available in more colors than any other kind of petunia. Overall, they make neat, compact plants that cover themselves in bloom.

Despite their many virtues, multifloras are less vigorous than other petunias and not really suited to center stage in the garden.

Milliflora. These dwarf petunias grow to about two-thirds the size of multifloras. Small, delicate, 1- to 1-1/2-inch blooms cover the compact plants, which are ideal for containers, window boxes, and hanging baskets. I plant millifloras as a border, spacing them about 8 inches apart. Plants form mounds 6 to 8 inches across. Don’t expect them to fill into a solid mass like other petunias. To show off the compact, dense mounds, plant them in clusters of three, five, or seven, depending on space. Space plants about 9 inches apart.

In the southern states (USDA Hardiness Zones 7 and warmer), millifloras are hailed as a long-lasting new bedding plant that won’t flop over. In zones 5 and cooler, some critics have noted a relative lack of vigor. My experience is different. I have enjoyed them for the last three years in Vineland, Ontario (zone 5), and find that when planted early and given good care, they are very welcome additions to the garden.

Unlike the multitude of series and varieties common to other petunias, only one type of milliflora is available: the Fantasy series, offered in nine colors.

Doubles. Grandifloras, multifloras, and some trailing types are available with double flowers. All of these novelties, but especially the trailers, are striking in mass plantings. My preference is to place them in beds or planters where you can see them at close range and appreciate the blooms’ complexity. While most double-flowered petunias are available as seed for home gardeners, seeds of doubles have less vigor so take longer to germinate and grow.

The Doubloon strain includes a solid pink as well as a veined pink, blue, and lilac. The more upright-growing Marco Polo, bred in Australia, comes in four clear colors: blue, rose, white, and a very showy pink. Both Doubloon and Marco Polo petunias are marketed under the Flower Fields brand.

Trailing types

Surfinia and other new trailing types were introduced in 1989, but only now are they becoming a market presence. They represent the first really new type of petunia in a generation.

Seed-propagated trailers. The Wave series is another star of the new trailing types. The incredibly vigorous ‘Purple Wave’ won an All-America Selections award in 1995. ‘Purple Wave’ was the first, and it continues to set the standard of performance, not only when compared with other trailing petunias, but also compared with sister colors in the Wave strain. Three new Wave colors were introduced in 1997: pink, lilac, and rose.

Wave flowers are multiflora-sized, 2-1/2 to 3-inches across, slightly larger than other trailing types. Although the flowers appear otherwise similar to Surfinia, and both types are hardy to about 28oF, their growth habits and leaf shapes are different. Wave petunias spread very rapidly, forming a low, solid mass studded with flowers. Plants remain about 6 inches tall and spread more than 5 feet across, making them a good choice for hanging baskets or patio pots.

Cutting-propagated trailers. Surfinias result from a cross of P. hybrida with a wild South American trailing type, P. pendula. They are remarkable for their long, trailing, dark green foliage that offsets flowers in five colors: blue-purple, pink, purple, violet, and white. Flowers are about 1-1/2 inches in diameter. Plant them in baskets, tubs, beds, or window boxes. In baskets, they produce trails of flowers. Their vigor can be a problem; it’s not easy to find a sufficiently large hanging basket and to keep it watered on hot days. A single plant can cover a 4-foot-diameter space, or trail that far out of a basket within four to five weeks!

Supertunias are modern hybrids of P. hybrida with another wild petunia, P. axillaris. These fast-growing, long-lived, profuse bloomers are ideal for hanging baskets, planting beds, and containers. Eight colors are available: burgundy, fuchsia, bright pink, pastel pink, dark purple, two types of violet-magenta, and white. Plants are slightly hardier–to 27° F–than Surfinias, so might be more likely to survive mild winters and serve as short-lived perennials. Their flowers are about 2-1/2 inches in diameter; plants will spread to 3 feet in six weeks. Both Surfinias and Supertunias are marketed under the Proven Winners brand.

Cascadias are Surfinia look-alikes. They share a similar hybrid history and are sold under the Flower Fields brand. Cascadias are available in 15 colors including several shades of purple, pink, and blue. For instance, uniquely colored ‘Charlie’ is blue with a soft yellow center. Cascadias also include a double-flowered strain, Doubloon.

Petitunia were introduced in 1998. Also marketed under the Flower Fields brand, it has the same vigorous and wide-spreading habit as the Cascadias, but its flowers are a diminutive 3/4 inch in diameter. The tiny flowers bloom in such profusion that the overall color impact is nearly equal that of its larger-flowered cousins. Colors include pink, purple, and white with darker veins. All four of these similarly vigorous petunias–Surfinia, Supertunia, Cascadias, and Petitunia–are propagated by cuttings only, not seed. Cutting-grown petunias are available at garden centers. As bedding plants, plant one per square yard. They’ll form a very dense carpet, with new shoots continuously producing blooms. Additionally, there’s no need to pinch off spent flowers, as old flowers dry up and fall off.

Growing petunias

Throughout most of the country, petunias are warm-season flowers that can produce a carpet of color from spring until frost. In intermediate- and low-desert areas such as Tucson and Phoenix, and in eastern zone 10, petunias fail in humidity or during extended periods of high heat (temperatures in the 90s), or both. In those regions, grow them as winter annuals, planting in fall and enjoying them through late spring.

Plant in full sun in rich, well-drained soil. If your soil is either very sandy or clayey, amend it by incorporating about 6 cubic feet of composted organic matter per 100 square feet.

Plant grandiflora and multiflora types about 10 inches apart, and Wave and Surfinia types 2-1/2 to 3 feet apart. After plants are established, pinch back halfway for compact growth. For optimum growth, feed monthly with complete liquid fertilizer. If you live in long-season zones 7 or 8, cut back plants halfway in August to force new growth.

Trailing petunias also need sun and well-drained soil, but they need more nitrogen fertilizer than bedding petunias because of their more rapid growth. An iron chelate spray or a nitrogen fertilizer with extra iron will promote attractive dark green leaves.

Pests. In humid weather, gray mold (botrytis) damages flowers and leaves of most types. There’s no practical remedy if you live in a wet-summer climate beyond planting resistant types, such as multifloras. The ozone in smog causes silvery spotting on leaves (petunias are so sensitive that they are good indicators of invisible ozone pollution). Tobacco budworm is a problem in some areas. Snails and slugs dine on petunias as well as other plants, and likewise, aphids may gather on succulent new stems.

Peter Kopcinski is a seedsman living in Marlton, New Jersey.

Photos by Suzanne DeJohn/National Gardening Association.

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