The contrarian rosarian–debunking rose mythology

Roses are perhaps the most frequently cultivated landscape plant across America. Rose gardens are common to parks, landscapes, botanical gardens and for homeowners. Everyone seems to have an opinion about rose culture and there are numerous clubs and societies to support the hobby of rose growing. This week I am in the midst of pruning my rose fertilizer study here in Santa Paula California. I have 240 roses of eight varieties and my thoughts are on roses now, so I offer this blog to dispel some of the myths about rose horticulture.

Myth I–Roses are difficult and require a lot of pesticides

Roses grow well in California soils. A selection of varieties here in Santa Paula CA

Most roses grow easily in most soils in most places. Roses tolerate environmental extremes very well. They grow in many climates and tolerate below freezing temperatures during winter dormancy and high temperatures during summer. Current rose varieties have been developed through breeding of wild rose types. Floribundas, hybrid T roses, grandifloras, shrub or landscape roses, climbing roses and dwarf roses offer the enthusiast a variety of forms and functions in the Rosa genus. In the early 19th century Empress Josephine of France gave rose development a great boost in her own garden at Malmaison. Her patronage of rose research led to the development of thousands of varieties in Europe and later in the United States. The genetics of garden roses is now quite diverse. Because of the diversity of roses some grow better than others, some are highly disease resistant some are very susceptible. Like all plants, roses develop various kinds of diseases and attract pests. Because they are grown commonly in gardens there are many rose pesticides available for use. In my decade of rose research growing hundreds of roses, I have never used pesticides to maintain them. Susceptible varieties could be treated with pesticides or gardeners can chose to avoid varieties that host pests and focus on ones that are not so afflicted. With so many varieties available to gardeners there will be strong varieties and weak ones, pest prone and healthy. The variety you select will determine the necessity for pest control. Many many roses are relatively pest free and grow well without any treatments.

Myth II Roses Require lots of irrigation

The idea that roses need more water than other landscape plants is a horticultural misnomer. In the Central Valley of California roses are grown for production to consumer markets and they typically are furrow irrigated once every eight days in the growing season. Even during triple digit weather, they are held to this schedule without damage.

Can you tell which one got Epsom salts? No. there is no difference between roses grown with applied magnesium sulfate vs those not receiving the treatment.

Myth III Roses require rose specific fertilizers

Roses need the same mineral element as other plants. There is no evidence that increased magnesium (Epsom Salts) benefits roses in any way. Prescriptive fertilization is not appropriate for rose culture or any landscape setting. Fertilizers should be applied on the basis of soils tests that determine the necessity of minerals that may be missing from the soil.

Rose varieties respond widely to field conditions. In the same field some varieties consistently thrive and others grow poorly. Rose varieties have variable vigor, tolerance of soil conditions and pest resistance.

Myth IV Prune rose canes at 45 degrees that is with angled Cuts

There are many pruning strategies for roses. One of the most consistent myths is that roses should be pruned with angled cuts so water is shed away from the cut end. There is no scientific basis for this and therefore it is not recommended. Pruning back to an outward facing bud is a good idea as it maintains a less tangled rose canopy and helps to promote a more organized architecture in the shrub. Various sources recommend more or less severe winter pruning for roses. Our research shows that the less severely you prune major canes the more flowers that will result. Severe pruning did not increase rose flower quality or quantity. The best rose shrubs (most flowers) are pruned to maintain their shape and reduce tangle while maintaining shrub size.  I almost forgot–Don’t seal pruning wounds made to rose canes.  Leave cuts to dry.

Myth V Mounding soil around the base of roses should be done every winter

Some rose experts, especially in places with cold climates have advocated mulching with manure or soil over the crown of the rose before freezing winter temperatures set in. Most rose varieties survive the cold winters without this treatment if snow is present. If temperatures fall rapidly without snow, a covering of leaves or straw may be helpful.

Myth VI Grafted roses are better than non-grafted roses

The recent advent of landscape or shrub roses has proven that this myth is incorrect. Non-grafted roses have the advantage of not producing annoying suckers that need to be removed frequently as on some grafted varieties. Many of the landscape roses growing on their own roots are more disease resistant, more vigorous, and produce more flowers consistently than their grafted counterparts. Not all scions are perfectly compatible with their rootstocks so some grafted roses are less vigorous due to graft incompatibility.

Roses are easy to grow once they are established. In recent years, I have had trouble with roses purchased from garden centers that would not grow when planted out. This may be because the plants were held too long in storage before coming to market. It is also imperative when first planting roses to frequently sprinkle the canes to avoid them drying out. Desiccation is a common killer of freshly harvested roses. Once buds “pop” and shoots emerge, culture can continue as with any garden plant providing appropriate moisture as needed. Fertilization should follow recommendations of your soils analysis.

Reference:

Downer, A.J., A.D. Howell, and J. Karlik. 2015. Effect of pruning on eight landscape rose cultivars grown outdoors. Acta Horticulturae 1064:253-255.

Published by

Jim Downer

Dr. Downer has 34 years of experience as a horticulture and plant pathology Advisor with the University of California Cooperative Extension in Ventura County. Dr. Downer’s academic training is from California Polytechnic Univ., Pomona, (BSc. horticulture & botany, 1981; MSc. Biology, 1983;. In 1998 he earned a Ph.D. in plant pathology, from University of California, Riverside. Dr. Downer’s research is focused on mulch, soil microbiology and disease suppression in mulched soils, diseases of shade trees and cultural practices to maintain landscape plants. Dr. Downer is a member of the American Society of Horticultural Science, the American Phytopathological Society, The International Soc. of Arboriculture, and the Western Chapter of the ISA, and the International Society for Horticultural Science. Dr. Downer is an Adjunct professor at California Polytechnic University in Pomona. Dr. Downer serves on the Board of the John Britton Fund for tree Research as the chair of the research advisory committee, and currently chairs the regional conference committee for WCISA. Dr. Downer has a love of shade trees, Shinrin roku (forest bathing/walking) tree work, wood working, horses, gardening, horticulture and the study of plants and their biology.

9 thoughts on “The contrarian rosarian–debunking rose mythology”

  1. Roses are some of the toughest plants I know, and some of the most invasive. R. multiflora was used as a root stock for ornamental roses and for roadside stabilization. It forms pure thickets and birds spread it…it climbs fully mature trees and they die, making it a forestry threat. Rosa rugosa an Asian beach rose is beautiful but invading shores in many parts of the world, also making pure thickets, eliminating shore bird nesting habitat, and resulting in erosion as it moves out the native grass species. Both are wickedly thorned making removing them highly unpleasant.

  2. Here in Michigan those landscape roses are now frequently planted in unfriendly places like next to parking lots and seem to thrive without a lot of attention. They bloom well into the fall. I don’t see many rose gardens using hybrid teas but the climbing roses do well. I have a Jacob’s Coat that has persisted in the face of almost no care (including irrigation) for years.

  3. It’s easier to talk about not spraying roses in CA where there’s no blackspot. In the hot, humid Deep South my bushes would be covered with blackspot if I didn’t maintain a regular spray program. Even Knock Out roses get it.
    I also can’t agree with you that own root bushes are more vigorous than grafted ones. Time and time again I have seen an own root bush take 3 or more years to catch up to the growth of my Fortuniana grafted bushes and some varieties of Minis and HTs just languish and won’t grow much at all unless grafted. This is borne out by many reviewers that contribute to Horizon Roses rose review publication.
    I do agree with you about not applying Epsom Salts and only fertilizing according to your soil test.

    1. Black spot is everywhere. It becomes a problem when environmental conditions, host susceptability, and disease virulence all coincide. “A regular spray program” is going to kill all your microbes, good and bad. That makes your roses more susceptible, not less. The publication you mention is not peer reviewed, and really is nothing more than a collection of anecdotal observations. They do not rise to the level of rigorous, peer-reviewed, experimental research.
      Dr. Downer is not only a plant pathologist, but does research on roses. You may not agree wtih it, but that’s where the science is, and this is a science based blog. Anecdotal observations are no more than just that.

  4. Oh man. I really want to read more about the best pruning practices! I tried to look up the article but could only get the abstract. Everything non-science-journal-ly I’ve read (rose books, etc.) has advocated pruning to about half height and eliminating “dead, damaged, diseased, or rubbing” canes. Is the half-height thing not supported by evidence? What about pruning off just the top bits where last year’s flowers were?

    Certainly when I get down into my shrub roses about 1/3 of the canes look diseased or half-dead. Is this covered by “maintain shape and reduce tangle?” I’d love to know the minimum pruning for the best result as that would save me a lot of work!

    I would love more information on the very best pruning practices for shrub (and climbing) roses, if anyone was able to write such an article.

    1. A rose is simply another woody plant. That means that the general rules about pruning any woody plant apply to roses, too. Roses do not have any special physiology or morphology that requires a unique approach to pruning or any other management practices. And there is no hard and fast rule about how much material to remove when you are pruning: the more you remove, the great a strain on resources you impose on the plant.

      Certainly the 3 D’s (dead, diseased, damaged) apply for pruning roses just like any other woody plant. But this too is smoething we are doing for our aesthetic enjoyment. Plants have mechanisms by which to prevent disease from spreading as well as the ability to shed dead tissues.

  5. British rose pruning study using controls undertaken some years ago by Royal National Rose Society had same basic outcome as that described here. That is that test plants mowed across the top like a hedge (pruned non selectively) bloomed more heavily the following season than those that got the long advocated opening up of the center selective pruning. With it being concluded that the reason for this difference was that the non selective treatment left the bushes with a greater total volume of stem tissue afterward. Stem tissue containing stored energy used to produce new growth with flowers on it.

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