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Plant Focus: Viola

March 3, 2020 • Leave a Comment

*Viola cornuta* (Photo: Jonathon Hofley / Michigan Gardener)

by George Papadelis

In the spring, the earliest bedding plants to appear at your local garden center are violas and pansies. These are usually available in flats and look similar except violas have smaller flowers than pansies. So, what is the real difference between violas and pansies and is this the same “violet” that has spread all over my friend’s yard? As a matter of fact, the plants referred to as “violas,” “pansies,” and “sweet violets” are all in the same group of plants, namely the genus Viola.

*Viola cornuta* ‘Jersey Gem’ (Photo: White Flower Farm)

Pansies are the result of crossing different species of violas. These “hybrids” (called Viola x wittrockiana) have flowers 2 to 4 inches across and include an incredible range of colors including white, black and practically every color in the rainbow. These plants will tolerate freezes and frosts, so gardeners can plant them as early as April 1 here in Michigan. They will flower profusely all spring and if old flowers are removed, they will most likely continue through the summer. The cool fall will encourage more flowering, which often lasts until the winter holidays. In our climate, pansies planted in a protected area usually return one more season for another performance, although somewhat less spectacular. Protected areas include the south side of the house and the cooler east side.

The smaller-flowering viola (Viola cornuta), sold in flats every spring, has evolved greatly. Several series such as the “Princess” series and the “Sorbets” have introduced new colors and color combinations that rival the closely related Johnny jump-up (Viola tricolor). Violas planted in our climate last one or two seasons. Just like pansies, spent flowers must be removed to encourage flowering through the hot summer.

Viola

Botanical Name: Viola cornuta (vy-OH-lah kor-NEW-tah)
Common Name: Violet, horned violet
Plant Type: Hardy annual/tender perennial
Plant Size: 5-10 inches tall
Flower Color: White, purple, violet, yellow, maroon
Flower Size: 1-1/2 inches wide
Bloom Period: Spring to fall
Light: Partial sun to sun
Soil: Well-drained, moist
Hardiness: Zone 5
Uses: Areas that are partially sunny, yet moist
Remarks: Remove spent flowers to encourage blooms through the summer

The dangerous member of this group is Viola odorata or “sweet violets” which are often just referred to as “violets.” These are very perennial, produce fragrant, small flowers in the spring, and may spread everywhere if you let them. Like violas and pansies, sweet violets produce seeds which may germinate and produce more plants. However, sweet violets also send underground stems called stolons in all directions, which may be difficult to find and remove. This invasive nature makes it an excellent groundcover or a wildflower in a naturalized site. Sweet violets have also been planted for as long as gardens have existed. The flower market in Athens, Greece sold sweet violets as early as 400 B.C. Its fragrance has been used by the perfume industry for centuries and is still being used by some today.

All members of the genus Viola produce edible flowers. Chefs all over the world use these showy blossoms as an attractive garnish, especially on salads. The blossoms also make great cut flowers and are among the most popular flowers for pressing. Members of the Viola family grow best in partial sun but full sun can be tolerated. High temperatures and drying out will cause stress, so keep the soil moist and cool if possible.

*Viola cornuta* ‘Cuty’ (Photo: White Flower Farm/Michael Dodge)

Gardeners looking for something different may want to try the purple-leafed viola (Viola labridorica) for its attractive foliage and fluorescent purple flowers. Other violas such as Viola koreana even have attractive silver patterned leaves. The bird’s foot violet (Viola pedata) is easy to identify because the leaves look just like a bird’s foot.

From a naturalizing habit to being self-contained, the genus Viola is so diverse that every gardener is sure to have a spot for at least one variety!

George Papadelis is the owner of Telly’s Greenhouse in Troy and Shelby Township, MI.

Tar spot on maple leaves

February 28, 2020 • Leave a Comment

Do the enclosed leaves come from diseased trees? There have been spots on the autumn leaves from these 2 trees for the last couple years, but not as many as last fall. They are the neighbor’s backyard trees, but the leaves fall into our yard. Are they dangerous to other growth or to the soil in our garden? The neighbor said if we wanted to have them cut down, he would not object.

The maple trees are infected with a fungus known as “tar spot” (Rhytisma acerinum). Many maple species are host to the fungus which is readily visible and, therefore, one of the easiest maple diseases to diagnose. Fortunately, it is one of the least damaging ailments on its host. It can cause early leaf drop but does not cause serious harm to established trees.

The tar-like spot is a fruiting structure of the fungus that survives the winter on fallen leaves. The following spring, just as new leaves are unfolding, the fungal tissue in the leaves on the ground ripens. The surfaces of the spots split and minute, needle-like spores escape. The spores are carried by the wind and, if they land on new leaves of a susceptible host, they may germinate, penetrate the leaf tissue, and start a new disease cycle.

Tar spot will not affect your soil health. Fungi are host specific and this fungus will only affect maple and sycamore trees. The most effective management practice is to rake and destroy the infected leaves in the fall. This will reduce the number of overwintering “spots” (fungal reproductive structures) that can produce spores the following spring. An almost as effective alternative is to mulch the leaves. But the mulch pile should be covered or turned before new leaves begin to emerge in the spring in order to destroy many of the spores before they mature.

What is quite interesting is that the apparent absence of the fungus in urban areas and abundance in rural areas has led to its use as a biological indicator of air pollution. Researchers think the absence in urban areas is caused by the amount of sulfur dioxide (exhausted by combustion engines) in the air.

Preferred growing conditions for redbuds

February 24, 2020 • Leave a Comment

I bought a 4-foot tall redbud and it has not grown at all. It leafs out, blooms for spring, then it looks dead by mid-August. Maybe it has verticillium wilt? Does this come back every year? If so, how do I prevent it?

Eastern redbud (Cercis canadensis) is highly valued in the urban landscape for its pink spring flowers and its smaller, manageable size. As an understory tree, it prefers moist, well-drained, deep soils. It tolerates various soil types, except those that are permanently wet, and adapts to full sun or light shade. Regular watering and fertilizing are keys to keeping it vigorous. Unfortunately, it suffers dramatically from lack of water, too much water, or mechanical injury.

Since your redbud does bloom and leaf out in spring, but looks dead by mid-August, your tree may be responding to inconsistent water patterns. There is plenty of moisture available in spring, from snowmelt and rain. By the apex of summer heat, the redbud may be packing all its energy into saving moisture for survival by dropping leaves and going dormant. This is not the typical pattern of a tree suffering from the soil-borne fungus verticillium wilt, which is incurable and progresses over time until the tree is dead.

Before assuming your redbud has this disease, consider the soil conditions where you planted it and your maintenance practices. Is the tree in the middle of lawn, competing with turf up to its trunk for moisture and nutrients? Is it subject to potential mowing damage? Has it ever received a slow-release granular fertilizer beyond its nursery container? Does it get regular deep watering during periods of no rain? With conscientious adjustments to maintenance and amendments, you strengthen your redbud’s ability to withstand such diseases as verticillium wilt, canker, and even insect pests.

With the new growing season upon us, re-examine your plant maintenance routine and strategize a consistent watering program as well as a spring and fall granular fertilizer application. If your tree is sited in lawn, remove the turf away from the trunk out to the tree’s drip line so the root zone has an equal chance for water. The redbud likes moist (not soggy) soil that is well-drained and rich, medium sunlight, and fertilizer to replenish what was used from its original container. Be observant about the tree’s progress through the season, and you may get to enjoy your redbud’s lovely yellow fall display.

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