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Petunia

Eva Monning Eva Monning

Petunias are captivating during the summer months with their vibrant flowers. You can read all about planting and caring for the different species and varieties here.

Origin and history

The plant genus Petunia (Petunia) belongs to the nightshade plants (Solanaceae) and is related to the Tobacco plants (Nicotiana), which is its namesake - ‘petun’ in the language of the indigenous Brazilian people means ‘tobacco’. It originates from tropical South America. Petunias belong to the group of garden flowers with the longest garden tradition because the magnificent summer flowers bloom tirelessly from May until the first frosts with large, vibrantly colored flowers. The Garden Petunia (Petunia x hybrida) came about in the 19th century from a cross of the Large White Petunia (Petunia axillaris) with the Violet Petunia (Petunia integrifolia). Most of the varieties which are currently commercially available are Garden Petunias.

Growth

From a botanical point of view, the Petunia is not a flower but a fast-growing, shrub-like herb. It’s appearance with funnel-shaped flowers on dark foliage is typical for the plant genus and easy to recognize. The classic Garden Petunia is sub-divided into four main groups: Grandilflora Petunias, which are a big hit with their over-sized flowers, Multiflora petunias with their compact growth and countless smaller flowers on short stems, the smaller-growing Nana Compacta Petunias at 5.9 inches and the elegant, hanging Pendula Petunias.

Hanging Petunias in a hanging basket

Hanging Petunias are ideal for flower boxes and hanging baskets

Leaves

Petunia leaves are dark green, full margined and slightly hairy. They are typically slightly sticky. They provide a rich, contrasting background for the fresh flower colors. Note: As the Petunia belongs to the nightshade family, their foliage is poisonous!

Flowers

Trumpet-shaped flowers in the summer colors white, pink, violet, red and blue with splashed, starred or striped patters which appear tirelessly in large numbers from May until October are characteristic of Petunias. The flower sizes vary according to Grandiflora Petunia and Multiflora Petunia. Grandiflora breeds are characterized by a very large, flat flower which sits on a single stem. Multiflora Petunia on the other hand have somewhat smaller, densely grouped flowers and have a more compact effect due to their shorter shoots. Double-flowered specimens are reminiscent of rose flowers, which is why they are also commercially available under the name Rose Petunias.

Garden Petunias are not always a single-color. You can now also obtain spotted or splashed and striped varieties

Location and Substrate

Petunias are typically summer blooming balcony flowers, which is why they need a lot of light. The plants also thrive in semi-shade, however then they develop fewer flowers. Hot summers and blazing sunshine do not damage these sun worshippers. However, their delicate flowers suffer greatly from cold, wet weather influences, so a sheltered location is recommended. Grandiflora Petunias should always be protected from the rain as their large flowers wash out quickly. The smaller the flower, the more robust the variety. There is special, ferrous soil commercially available for flower containers and boxes with a low pH value (approx. 5.5), which is well composed for the requirements of these plants. Alternatively, normal planting soil can be mixed half and half with bog-flowerbed soil as a substrate.

Planting and Care

Petunias can be sown in propagator pots in the greenhouse or on a window ledge from mid-February at 68 to 70 degrees Fahrenheit. The seedlings can then be slowly acclimatized to the fresh air after the last frosts have finished. However, they are normally sold as young plants in a pot which can then simply be directly planted in the desired position during early summer.

The plants should be regularly pruned to stimulate beautiful growth in the petunias. During pruning, the deadhead, wilting shoots and damaged parts are removed. Occasional trimming also stimulates flower development. They require plenty of soft water (rain water) during hot mornings and evenings. Always water directly into the soil and do not shower the leaves or flowers! The colorful summer bloomers are extremely fast growing and therefore require a lot of nutrients. They have a strong uptake and require extremely permeable, nutrient-rich soil. They should be fertilized with high-phosphorous flowering plant fertilizer.

Petunias in flower boxes

To ensure petunias flower vivaciously the key is: fertilize, fertilize, fertilize

Overwintering

Garden Petunias are annual and not frost-hardy. If you wish to overwinter the plants, you can do so in a light, cool space (41-50 degrees Fahrenheit). The plants should also be heavily pruned. The plants should be put away before the nighttime temperatures drop below zero. They require regular watering in small quantities during the winter months.

Where to plant

Petunias are a popular plant for pots, flower boxes and hanging baskets thanks to their lush growth and abundance of flowers. Whether as a solitary plant or as under-planting for standard plants such as Roses or Lantana camara – the colorful blooming wonder looks great anywhere, provided it can get enough sunlight. Garden Petunias are also happy accompanying other annual summer bloomers in flower beds. Just don’t place the fast growing Petunias next to partners with weaker growth rates. Suitable neighbors for Petunias include, for example, Chaenostoma cordatum, Marigolds, verbena, Pelargonium, Ipomoea, lobelia, Dahlia, Fuchsia or Echinacea. Petunias belong to the classic farm garden plants, so they can be used decoratively with vegetable plants or herbs in boxes, tubs, containers or troughs. Decorative grasses provide a delicate contrast and relax the petunia flowers, which can sometimes be a little too gaudy. Ornamental foliage plants such as Ground Ivy or Variegated Nettlesalso provide visual calm to the planting.

Varieties

Small flowering varieties are currently in fashion, such as Million bells (Calibrachoe), which is available in a variety of colors. These are extremely visually similar to the Garden Petunias, however, they belong to a different genus from a botanical perspective. Full colored varieties from the Bonanza series are also a firm favorite. The ever popular Petunias in balcony and hanging basket planting include Cascade Petunias, such as ‘Giants of California’, whose long shoots gush over boxes and railings like a waterfall of flowers. The Plum Petunia displays veined flowers. If you prefer things a little more subtle, you’re better off trying the Celebrity series. This breed specializes in flowers in fine pastel shades with a light throat. A new Japanese breed is the extremely robust Surfina petunia. Its large flowers are also resilient to longer heavy showers.

Surfinia Petunia

These yellow-flowering Surfinia Petunias are a delight in pots and containers

Propagation

If you would like to propagate a variety which you have come to love, you can collect seeds from the deadhead plants in the fall. In this case, do not prune the Petunias, rather wait until the seed capsules have formed. You can then harvest these and leave them to mature in a warm space. If the seed capsules crack open themselves, you can collect the seeds and store them in a cool, dry place. Seeds are sown under glass in February. If seedlings have formed, the Small Petunias thinned and isolated in pots. Caution! Many modern breeds are created as disposable products and therefore do not bare seeds which are capable of germinating. Find out in advance from your specialist dealer whether it is worth the effort of sowing the seeds.

Diseases and Pests

Petunias are susceptible to Fusarium oxysporum and Powdery Mildew. The Tobacco Mosaic Virus is also occasionally bothersome for these summer flowers. You should look out for wilting leaves or white patches when purchasing plants. It’s also necessary to regularly check the balcony flowers for Aphid and White fly infestations. Petunias often suffer from snail damage in the garden. If the leaves suddenly turn yellow on the summer bloomers in pots and containers, this probably indicates a lack of iron (Chlorosis). This can be seen on the renewed, young leaves. Administering ammonium-containing fertilizer helps.

Frequently Asked Questions

When are petunia seeds sown?

Petunias can be sown from mid-February, ideally in propagation pots on the window ledge or in a greenhouse at 68 to 70 degrees Fahrenheit.

When can Petunias be planted?

If you obtain young plants commercially, these can be planted in early summer in the desired place.

What kind of soil is suitable for Petunias?

If you would like to plant Petunias in a flower box or hanging basket, you can use a soil specially created for Petunia requirements or mix normal potting soil with bog flower bed soil.

How many Petunias can be planted in a hanging basket or balcony box?

Petunias can grow up to 16 inches wide, depending on the species and variety. A planting distance of approx. 7.86 to 9.84 inches is recommended to ensure the balcony flowers do not feel too cramped.

When can Petunias go outside?

Petunias can be taken outside after the last frosts, so from around mid-May.

Are Petunias perennial?

No, the typical Garden Petunia is annual.

Are Petunias sensitive to frost?

Yes, unfortunately Petunias are sensitive to frost. A cool space between 41 and 50 degrees Fahrenheit is suitable for overwintering.

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