Large white petunia (Petunia axillaris) Care Guide
Large white petunia is not difficult to grow or maintain and presents no particular challenges provided the soil is kept reasonably dry. Large white petunia is used for its delicate, colorful flower booms, pleasing scent and its flowering duration which lasts from spring until frost. They make excellent bedding and container plants.
Quick Care Guides
Water and Hardiness
On account of its South American origins, large white petunia can tolerate high temperatures but will not tolerate frost. Though classed as tender perennials, most large white petunia will not survive winter conditions and live as annuals. They are not a hardy genus and will only survive in a warm area. Night-time temperatures should stay above 14 ℃ and daytime temperatures above 16 ℃.
Large white petunia likes moist substrate but does not tolerate waterlogging, because soggy soil will cause root rot.
The most important factor in growing of large white petunia is sunlight. large white petunia needs at least five hours of sunlight per day. They will thrive best and grow the most flowers with exposure to full, all-day sunlight. The plants will grow in partial shade but will have fewer flowers. Lack of sunlight may also lead to leggy plants and a lack of healthy flowering.
large white petunia will thrive best in fertile soil with high organic matter content such as peat moss, well-decomposed compost or manure. If potting, soil needs to be lightweight to allow water to drain away. Dense soil with poor drainage is easy to accumulate water, making large white petunia roots wet and causing them to rot away. As with many ornamental plants, petunias prefer slightly acidic soil (pH 6.0–7.0).
Large white petunia can be grown from seed though growing from transplants is easier. Transplants should be positioned in light, well-drained soil with exposure to full sun shortly after the last frost in spring.
If growing from seed, start the seeds indoors 10-12 weeks before taking them outside. The seedlings can be taken outside once they have three leaves, and the placing of plastic wrap over the seedlings outdoors will help keep temperature and humidity constant to help in their development.
Whether growing from seed or transplanting large white petunia, a location should be chosen with minimal exposure to wind and each plant given a space of 30 cm. Large white petunia should not be planted in the area where diseases have once occurred, since they are susceptible to diseases. If planting in pots use a soil-less mix to keep cultivation substrate light large white petunia free of disease.
Watering of large white petunia once a week should be sufficient in most conditions but large white petunia plants in hanging baskets and other containers may require watering more frequently, especially in hot summer. A good watering medium is the use of a fine spray mist applied to soil and foliage to avoid water-logging of soils that can damage roots.
In summer, a balanced liquid fertilizer contains roughly equal proportions of the three main elements (N％-P2O5％-K2O％) with 8-8-8 or 12-12-12 can be used every two to three weeks. Spreading varieties will respond well to weekly fertilization. Some varieties such as those with double flowers will enjoy twice-weekly doses of fertilizer. If growing large white petunia in containers or baskets, opt for a time-release fertilizer.
During the season, deadhead any flowers which have died to keep the area free of sites which may harbor pests and disease. Large white petunia flowers die fairly quickly so deadheading should be performed regularly. Doing so will help the growth of new flowers and prolong blooming.
My large white petunia is wilting. What is the problem?
Large white petunia may wilt if soils become too water-logged or if they are dry. Too little or too much water will reduce root growth and cause the plants to wilt. If this is noticed, first check to see if the soil is very dry. If so, water the plant. If it is too moist, waterlogging may be the problem. Waterlogging is the most common problem to large white petunia and will manifest as wilting plants. Soil should be dried out at least once before watering the plants.
My large white petunia is growing very few or small flowers. What is the problem?
My petunias have grown leggy with droopy flowers. What should I do?
Large white petunia stems may sometimes grow long and flowers droop. If this has happened, petunias should be trimmed back in midsummer by removing half of the plant stem’s length using garden shears. this will force the flowers to grow new, more compact stems and full flowers. Remember to put your large white petunia in a place with plenty of sunlight.
Pests and Diseases
Grey mold, also known as Botrytis blight, will manifest as spots or discoloration on large white petunia flowers and leaves that eventually form spores. Unlike other diseases such as crown, root or stem rot, grey mold can be treated through pruning of the affected areas and removing any surrounding soil debris. Watering should also be lightened to help remove moisture from the area. Too much moisture will help the disease to propagate. Once treated, the bed should be dried out at least once to help prevent re-infestation.
Fusarium wilt affects many plants. In large white petunia, it manifests as yellowing of the leaves. The best prevention is to ensure the planting of disease-resistant varieties at the beginning. However, if suspected, Fusarium wilt can be treated using Mycostop biological fungicide according to manufacturer instructions. If this does not work, be sure to remove the infected large white petunia and any nearby plants to help reduce the risk of the infection spreading.
Spider mites are tiny, almost-microscopic cousins of spiders that suck the juices out of flowers such as large white petunia. They remove nutrients from the plants as well as causing mechanical damage by their sucking action. Mite damage can be identified by the curling up of large white petunia leaves and petals. These pests can be prevented by applying an oil insecticide to the top and bottom of foliage at the beginning of the season. A horticultural oil-free of petroleum should be used with one tablespoon of the oil mixed into one liter of water. If mites have already taken hold, a weekly spray of neem oil will remove them from the plants.
As well as damage caused by thrips themselves, thrips can carry viruses between plants. Thrip damage can be identified by leaves turning dry and papery. It can also manifest through white spots in flowers breaking up the flowers’ colors. As with Mites, a horticultural oil-free of petroleum can be used with one tablespoon of the oil mixed into one liter of water to prevent these pests. If already on the plants they can be treated through a weekly spray of neem oil.
Other Uncommon Pests or Diseases
Moreover, there are some less common pests and diseases listed below that need your attention.
- Powdery Mildew
- Late Blight
- Brown Spot
- Root, Stem and Crown Rots
- Verticillium Wilt
- Virus Diseases(Cucumber mosaic virus, Tobacco mosaic virus, Beet curly top virus, Impatiens necrotic spot virus, etc.)
- Leaf Miners
- Snails and Slugs