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2014: Year of the Petunia

This petunia hybrid known as vista bubblegum has been grown at McCrory Gardens in Brookings. (McCrory Gardens photo)

By David Graper

Each year the National Garden Bureau selects a perennial, annual and edible to become the chosen plants of the year. This year they have chosen petunia as the annual of the year.

It is difficult to think of an annual garden or container that does not include at least a few petunias. They now come in such a staggering array of colors, flower sizes and growth habits that they fit into just about any situation. They are very easy to grow, have few pest problems and can bloom from early summer until a hard freeze in the fall.

Petunias are native to South America but the hybrids that we buy today have come a long way from their natural ancestors. I think I might have actually seen some native petunias when I was in Bolivia back in 2001, but they were much plainer, with fewer and smaller flowers than most of the cultivars available to us today. Much of that is due to the art and science of plant breeding which continues to bring us an ever increasing diversity of plants with traits unseen and even unthought-of just a few years ago.

One of those advances has been in the development of inter-specific hybrids or the crossing of two different species and inter-generic hybrids or the crossing of two different genera. Typically plants have to be in the same species in order to successfully cross but inter-specific hybrids are very common now. Inter-generic hybrids are becoming more common as well. In the case of petunias, it means crossing with a fairly close relative, Calibrachoa to produce what are sometimes known as Petchoas. When you start looking at the great diversity that is already out there and then start thinking of all the different combinations that are still left to try -- I think those plant breeders are going to be busy for a long time.

Keep it simple

Petunias are classified in a number of different ways depending on the flower size, plant size, plant growth habit, numbers of flowers produced, color and of course parentage. Some of the different types include multiflora, grandiflora, floribunda, milliflora, spreading and wave. Each major seed company has come up with their own "brand" or series which can make it a bit confusing as to which petunias to buy for your yard or garden.

Don't make it too complicated. Buy and plant what you like. If you have some cultivars that have performed well for you, grow them again. But be sure to check out the "new kids on the bench" at your local garden center. Generally, you will be able to learn a little more about how that particular plant will grow by reading the plant tag in the pot or pack or look for a bench card that might provide you with even more information. Certainly speak to the staff of your local greenhouse or garden center to see if they can provide any assistance in plant selection of your petunias and any other plants they might be selling. They should be able to tell you more about how different plants might perform in garden beds or containers.

Buying petunia plants from your local garden center is certainly the easiest and probably the best way to get started in growing petunias. You will usually find them sold in cell packs or in small pots when it comes to the spreading types.

If you are looking for a little challenge, you can also grow them yourself from seed, but it takes quite a while to get from planting the small seed to having a nice plant blooming in a pot on your deck or in your garden. The benefit is that you might be able to locate the seed of a stunning new cultivar that you might not be able to find for sale in your home town. But, it will often take about 12-15 weeks to go from planting the seed to having a plant large enough to transplant outside. The seed is fairly small, so look for pelleted seed if you can find it.

Check online for the best selection. Petunias need lots of light to grow too. In fact, commercial growers often use supplemental lighting on them while they are already in a greenhouse. So start them in a warm location and place them a few inches beneath fluorescent lights or on a very sunny windowsill if you want to try growing your own.

Petunias grow well when planted directly in the ground, often despite our clay type soils. However, sometimes we have seen some of the smaller-flowered types, like the Calibrachoa or Million Bells cultivars will suffer in heavy soils and not bloom as well. They will grow better in a soil that has better drainage. So, if your soil is pretty heavy, try creating a raised bed, mix lots of organic matter into the soil or try a container. Petunias get along with most other plants but can sometimes overgrow their neighbors so give them space to spread out a bit. Check the plant tag to see how big the plants will generally grow before planting so that things do not get too crowded. The nice thing about petunias though, is that they are pretty adaptable and will grow to fill the space and probably bloom like crazy the whole time while doing it. Petunias will flower best in full sun but can tolerate some shade as well. Once they are established, they can also tolerate some drought but don't let them get too dry or flowering will decrease.

New releases

There have been lots of great new petunias introduced over the last several years. Some of the best ones from our trial program at McCrory Gardens include: Petunia "Cha-Ching Cherry"; "Debonair Black Cherry"; "Flash Mob Bluerific"; "Pretty Much Picasso"; "Suncatcher Vintage Rose"; "Rose and Shine"; "Shock Wave Deep Purple"; "Vista Bubblegum"; and "Vista Silverberry." We have especially enjoyed some of the new multi-colored and multi-patterned cultivars. However, we continue to be a bit disappointed in the lack of a few, true, very important colors, especially for us here on the campus of South Dakota State University -- blue and yellow.

There are probably dozens of petunias that have blue in their name, but I have yet to see one that is a true blue and not really purple or lavender. Likewise, I have yet to see a good solid yellow petunia. There are some light yellow cultivars out there but the flowers usually fade out fairly quickly. Orange petunias are also not quite there yet, but there is a newly announced All America Selections 2014 Winner called "African Sunset" that is said to be a "designer orange." Yes, there are hundreds of cultivars to choose from, but I think the plant breeders still have some work left to do.

Healthy plants

Generally we do not see many pest problems or diseases on petunias. The most common pest problem is usually aphids or whiteflies but they usually show up in the greenhouse and are not a problem in the garden.

Spider mites can be an issue but usually during the summer when it gets really hot and dry. These might be especially troublesome for petunias, and other plants, growing in a container in a hot location.

Petunias are also susceptible to iron chlorosis when planted in high pH soils. You will especially notice this during cool wet periods or in more poorly drained soils. Regular fertilizing with a product that has micronutrients included should help to keep your plants green, growing and blooming.

-- Source: SDSU Extension. Graper is an SDSU Extension horticulture specialist and director of McCrory Gardens.