Crop Vignette: Rose

This first appeared as “Spotlight on Ornamentals: A rose by any other name” in the IR-4 Newsletter 48(1):8.

Plant Information

A dozen long-stemmed roses is the modern epitome for giving a gift on Valentine’s Day to one’s sweetheart. The tradition of giving flowers as presents may have arisen in the early 18th century when King Charles II of Sweden visited Persia and returned home with a new art: the language or flowers, otherwise known as florigraphy. It became highly fashionable to send messages to one another by sending flowers. As this practice gained in popularity, Chelotte de la Tour from Paris codified the language in the first flower dictionary “Le Language des Fleurs” published in 1818, which further increased the practice and spawned additional reference books on the topic. The nobility and developing middle class equated knowing and using florigraphy with other valued trains of gentry such as good manners and being well groomed. Sending flowers wasn’t just for romance. The language of flowers had depth and breadth and conveyed many emotions and meaning. For example, sending fennel meant the receiver was worthy of praise. Some flowers had multiple meanings such as yellow roses could signify both friendship and betrayal. Red roses meant passion and romantic love. With Valentine’s Day celebrating romantic love with sending gifts and notes of affection with one’s sweetheart, sending flowers became an elegant and nuanced way to convey one’s feelings from friendship to disdain to passion. While much of the language of flowers has faded away, we still give flowers on major events – including sending red roses to one’s valentine on Feb 14.

Whether as flowers in bouquets or bushes in landscapes, roses fill major niches in our urban plant world. According to the 2014 USDA NASS Census of Horticulture, the wholesale value of all roses grown in the U.S. was $262 million. More than 75% of these were shrub roses for landscaping around homes, businesses and public areas.

Main Disease and Pest Problems

During production and in the landscape, roses are prone to numerous diseases and pests. Some of the diseases include powdery mildew, downy mildew, black spot, and gray mold (Botrytis). Thrips, scale, mealybugs, mites, eriophyid mites and Japanese beetle larvae and adults feed on roses, causing damage and possibly defoliation. Some pests vector diseases. For example, eriophyid mites move rose rosette virus from infected plants to healthy ones nearby. This disease started in the Rocky Mountains in the beginning of the 20th century and has progressed across the U.S. so that it is impacting naturalized multiflora rose (an invasive weed!) and landscape roses in eastern states today.

IR-4 Research

Since the inception of the IR-4 Ornamental Horticulture Program in 1977, we have screened 56 products for crop safety, four for PGR affects and 93 for efficacy against diseases, pest and weeds of roses. This had lead to registration or label amendments for more than 50 products. A recent example of success is the development of data for gray mold caused by Botrytis cinerea. In California, Dr. Cai-Zhong Jiang studied the impact of several fungicides on the development of gray mold on ‘Karina’ miniature rose. Relying on nature infections, Orkestra (BAS 703) demonstrated superior disease development prevention (Table 1). This efficacy report became part of a larger data set to support registration of Orkestra to manage Botrytis on ornamental horticulture crops.

IR-4 will continue to aid rose producers to grow the best possible flowers, so you will be able to continue to enjoy giving or receiving beautiful long stem roses on Valentine’s Day, and landscape rose bushes in your yard.


Rose Growing Tips From

America’s most popular flower is also one of the very oldest flowers in cultivation. There are over 2,000 different rose varieties to lure us with their history and fragrance. This is because the rose, like the orchid, cross-breeds readily—a trait exploited first by nature, and then by horticulturalists. Today, we can choose from old-fashioned favorites, as well as modern varieties that are the result of intensive breeding programs throughout the world. The rose is a flower with a rich past, and an exciting future.

Finding your way through the rose’s large extended family can be both confusing and intimidating. Damasks, musks, gallicas, centifolias, hybrid perpetuals, Bourbons, hybrid teas, ramblers and climbers—even the most distinguished rosarians have a difficult time determining which rose is which.

Tracing the history of a particular rose can be a fascinating adventure, but it is hardly an exact science. The old roses have cross-bred so many times, and so many varieties have been lost to time, that it is often impossible to uncover the exact parentage. If you are one of the many who become possessed by roses, you may eventually find it important to know the difference between a gallica and a Bourbon. But until that point, our advice is not to worry about it. The important thing is to select a rose that you find beautiful, and that suits your garden.

Roses are usually grouped into one of two broad categories: old roses and modern roses. Old roses are those varieties discovered or developed prior to the introduction of the hybrid tea rose in 1867. But like everything else in the world of roses, when it comes to determining how a particular rose should be classified, it’s not always crystal clear.

It is generally agreed that “old roses” include species or wild roses; albas; Bourbons; moss roses; China roses; Noisettes; Portland roses; rugosa roses; Scotch roses; centifolias; hybrid pimpinellifolias; damasks; gallicas; hybrid perpetuals; tea roses; and musk roses. Those classified as modern rose varieties are hybrid teas; floribundas; polyanthas; grandifloras; miniatures and dwarfs; modern shrub and landscape roses; climbers and ramblers; and rugosa hybrids.

Why choose an old-fashioned rose over a modern hybrid? Many of the old rose varieties offer more fragrance, more complex and interesting blooms, greater disease resistance, easier care and more interesting forms. But modern roses can offer all-season blooms, and a much broader range of colors and flower forms. Some are also far more cold- hardy and disease-resistant than any of the old-fashioned varieties.

How to Select a Rose
There are thousands of beautiful roses, far more than any of us will ever have the opportunity to see, much less grow. When choosing a rose for your garden, there are five considerations that should make the selection process easier.

1. Growth habit
Though roses are usually planted for their flowers, it is important to know what the plant as well as the flowers will look like, in order to determine where it will fit in your garden.

Hybrid teas and floribundas usually grow no more than 2 to 3 feet high. Their form is coarse, and hardly very appealing, but they do have the ability to produce an abundance of flowers throughout the growing season. The hybrid tea has large, single blooms on long, stiff stems, whereas the floribunda has slightly smaller clusters of blooms on stems that are not as stiff.

Miniature roses have tiny flowers, and may be only 10 to 36 inches tall. Dwarf roses grow up to 2 feet high, and their flowers are produced in clusters. Shrub roses, including both the old-fashioned and the modern types, and ground-cover or landscape roses, are generally large and leafy.

Climbers and ramblers grow from 7 feet to 30 feet in length, and most of them benefit from some support. Standards are roses that are trained into a tree-like form with a single stem and a rounded bush or weeping display of flowers on top.

2. Hardiness
Northern gardeners need to know exactly what zone a rose is hardy to. Southern gardeners must also watch to see what zones are recommended for each particular variety, as some roses perform very poorly in hot and/or humid weather. Read the catalogs carefully and, if possible, purchase your roses from a local or regional grower. They will be able to advise you from experience about how a particular variety will perform in your area.

3. Bloom time
Many roses, especially the old-fashioned varieties, have just one flush of blooms per year. Will you be satisfied with a cloud of heavenly pink blossoms for three weeks in June, or do you need your rose to bloom all summer long? This consideration may narrow your choices very quickly.

4. Disease-resistance
Selecting a disease-resistant rose is the single most effective way to avoid problems and the need for chemicals. You might start by considering some of the old rose varieties, many of which have natural disease resistance. You can also look to many of the modern roses, which are now being bred for improved disease resistance. Hybrid teas are notoriously disease-prone, and seem to lure every insect pest from miles around. They can be difficult to grow without an arsenal of chemical dusts and sprays.

5. Stem length
This may seem like an odd consideration, but it’s important if you are growing roses for cutting. The traditional florist rose is a hybrid tea, and it is the only type of rose that flowers on a long, stiff stem. All other roses have shorter, weaker stems, which gives them a more casual—some believe more beautiful—presence in a vase.

Caring for Your Roses
Roses are rather particular, and you should be aware of the growing conditions and care necessary to keep them happy.

Site: For most abundant blooms and greatest vigor, roses need to receive 6 to 8 hours of direct sunlight each day. In hot climates, they will appreciate receiving protection from the most intense afternoon sun. In cool climates, a fence or a warm south- or west-facing wall can add enough extra warmth to boost flower production and reduce winter damage.

Soils: Roses need good drainage and a rich, moisture-retentive soil, with a pH between 6.5 and 7. If your soil is heavy and wet, you may want to consider planting your roses in raised beds. Compost should be added to create a loose texture with a high organic content. For help correcting a pH imbalance, read Building Healthy Soil.

Water: Roses require more water than most other landscape plantings, especially during the first year as the plant is getting its roots established. The best way to water your roses is with drip irrigation. It concentrates the water at the root zone where it is needed, and keeps the foliage dry to minimize disease problems. A good, thick layer of organic mulch will help conserve moisture, reduce weeds, and encourage healthy root growth. As the mulch breaks down, it will also add organic matter to the soil.

Fertilizer: Roses are heavy feeders, and will benefit from a steady supply of nitrogen, phosphorus and potassium. You can provide these nutrients with either liquid or granular fertilizers, at a ratio of approximately 5-8-5. In most cases, regular applications of compost, rotted manure, fish emulsion and seaweed extracts will provide roses with all the nutrients they need. These organic amendments also help to moderate pH imbalances and stimulate beneficial soil life. Other organic amendments favored by rose growers include greensand, black rock phosphate and alfalfa meal.

Pruning: Dead, weak and sickly stems can lead to disease problems. Pruning these away will increase air circulation to the center of the plant and minimize fungus problems. Pruning also stimulates new growth, and allows you to shape the plant in a pleasing manner. Spent flowers should be removed during the growing season to encourage reblooming. Use a scissor-action pruner for the cleanest cuts.

Winter protection: If possible, select rose varieties that are hardy for your growing zone; ones that can survive the winter with no special protection. In cold climates, hybrid teas and floribundas, as well as some of the smaller shrub roses, will benefit from a little extra insulation. Once you have had several weeks of below-freezing temperatures, cover the base of the rose with 12 inches of soil or mulch, and then cover the canes with straw, leaves, pine boughs or even foam insulation. Climbing roses can be wrapped right on their supports, or you can lay them on the ground and cover the canes with straw or brush. In severely cold climates, hybrid teas are sometimes partially dug up, laid down onto the soil, and the entire plant is then covered with more soil or mulch.

Pests and diseases: Prevention is the best way to avoid pest and disease problems. Start with disease-resistant varieties, keep plants in healthy condition (well fertilized and well watered), maintain good air circulation, keep foliage dry, and remove any diseased foliage or spent flowers. For Japanese beetle grubs, use beneficial nematodes or Milky Spore (Bacillus popilliae). Rose Rx is effective against scale, spidermites and aphids. For more information, see the Pest and Disease Finder.

Sources Cited