Culture of Roses

Aug 01 2007

Culture of Roses

Posted by: Leo in Plant & Crops 849 Views

Beginners and “old pros” alike can profit from the experience of others when selecting rose varieties. By visiting botanical gardens and talking with local gardeners, nursery producers and garden store operators, you can learn which varieties are best adapted to your area.

Most rose enthusiasts agree that roses require extra-tender loving care, but the rewards are well worth the effort. The following guidelines will make your rose growing experience more successful and enjoyable.

Picking the Planting Site

Many rose failures can be linked directly to poor site location. A site that provides sufficient sunlight, good soil and good air flow is of utmost importance.

Roses require a minimum of six hours of sunlight each day. Where some shade cannot be avoided, a location with morning sun is best. Morning sun will help dry dew from the foliage and reduce leaf diseases.

Next to sunlight, nothing is more important for successful rose culture than the soil. Roses require a well-drained, moderately fertile soil having a pH of 5.5 to 6.5 Air spaces between soil particles are essential for air and water movement into and out of the soil. The fertility and acidity of a well-aerated soil are also easier to correct and maintain than those of a more compact soil. Sandy soils generally have adequate air spaces between particles while heavy clay soils may require sand or organic matter to increase aeration. Failure results if the rose bed is located in a poorly-drained area of the landscape. If you cannot avoid a poorly-drained site, raise the bed with 6 to 8 inches of topsoil.

Preparing the Soil

Thoroughly plow or spade the planting area at least 12 inches deep and remove any rocks or debris. A more desirable practice is to prepare the soil in an entire bed instead of digging individual holes. A 4-inch layer of organic matter such as peat moss, composted pine bark or leaf mold incorporated thoroughly into the bed may be beneficial in certain soils. Some rose growers also incorporate natural organic fertilizers such as cotton-seed meal, milorganite or manure into the planting bed.

If you are serious about top-notch results from your roses, you may wish to fumigate the bed before planting. Many soil-borne insects, diseases and weeds can be eliminated by soil fumigants.

Buying Plants

Expect to pay higher prices for better quality plants. Buy from reputable sources — a licensed garden center or nursery, an established rose company or a well-known mail-order source. Cheap plants are just that — cheap — and will often produce poor growth and flowers the first year.

Rose plants are usually graded No. 1, 1½ and 2 based on size and number of canes. Grade No. 1 indicates top quality. These plants have three to five canes (? inch diameter or larger) 18 inches long. Grade No. 1½ will have two canes 15 inches long. Grade No. 2 will have two canes 12 inches long (Figure 3).

Figure 3. Packaged bare-root roses are available in three grades.

Buy plants with vigorous looking canes and avoid those that appear shriveled or discolored.

In recent years, roses have also been marketed as container-grown plants. They transplant best during the spring and early summer months. Container-grown plants generally have a better root system than bare-root stock and so suffer less transplanting shock.

Selecting Rose Cultivars

Selecting roses can be a confusing task. There are more than 6,000 rose cultivars (propagated varieties) having a wide variety of flower colors and growth characteristics. Your choice will depend on your personal preference for flower color, growth characteristics, plant performance and availability.

Roses are classified according to their growth habit and flower form. The following are the major classifications of roses.

Hybrid Tea: Hybrid tea roses are the most popular class of rose on the market today. Plants are strong and upright in growth habit and have large flowers borne singly on long stems. Hybrid tea roses make excellent arrangements and are preferred by florists.

Floribunda: As the name implies, floribunda roses flower abundantly throughout the growing season. Flowers are smaller than those of the hybrid tea roses and are borne in bouquet-like clusters. Some cultivars are low growing and are often grown with annuals and perennials in beds or borders.

Grandiflora: Plants of the grandiflora class combine features of the hybrid and floribunda roses. Flowers are borne in clusters like floribunda roses and have the form and long stems of the hybrid tea roses. The flowers are smaller and plants are taller than those of hybrid tea roses.

Climber: Climbers are a large class consisting of many different sub-types. Climbing hybrid teas are mutants of hybrid tea cultivars that are vegetatively propagated for their climbing growth habit. Trailing climbers can be grown on walls or as ground covers on banks. Ramblers are still another type of climber. They form dense clusters of small flowers on long, vigorous canes and may grow as much as 20 feet in a single season.

Miniature: Flowers and leaves of miniature roses are smaller than those of other types of roses; however, plants are not always miniature in size. Some miniature rose plants may grow from 4 to 6 feet tall at maturity.

“Old Roses” and Species Roses: Old roses are cultivated garden roses that were in existence before 1867 and have remained genetically pure through the years. These include the European and Chinese ancestors of today’s “modern” roses. Growth habit and flower form of old roses are quite diverse. Species roses are the native or naturalized roses propagated and sold commercially.

Planting

Container-grown plants are a better choice for late planting.

Spacing the plants in the rose bed depends on the variety and the growth rate. An average spacing is 3 to 4 feet apart. A 5- to 6-foot spacing is recommended for vigorous growing varieties.

Dig a hole large enough to accommodate the root system without crowding. Planting depth is critical. Plants set too deeply do poorly and are more susceptible to pests.

To set the plants at the correct depth, construct a cone-like mound of soil in the middle of each hole. The cone should be high enough so when the plant is set on top, the level of the graft union (the swollen area of the main stem) is about 1 inch above the soil level. Separate and spread the roots around the cone (Figure 4). Partially fill the hole with soil, shaking it between the roots. When the roots are covered, fill the hole with water and allow it to soak into the soil. Then finish filling the hole. Use your hands to build a ring of soil about 4 inches high along the perimeter of the planting hole. This directs water to the roots while the plant is getting established. Water thoroughly several times to settle the soil around the roots.

Figure 4. Dig large holes. Avoid setting plants too deep. Mound soil in the hole and spread roots over the mound.

After planting bare-root plants, prune the canes back to 5 to 7 inches in height. Remove any broken or discolored canes. In the colder, mountainous region of Georgia, mound soil up over the canes to protect them from cold damage during the winter. Remove the mounded soil as soon as the danger of frost has passed or as new growth begins.

Plant container-grown roses no deeper than they were in the original container. If the root system is pot-bound, loosen it with your hands before planting.

Plant individual plantings similar to bedded plants. Dig the planting hole two to three times wider than the root system and 12 to 15 inches deep. This loosens the soil in a large area and provides a favorable environment for root system growth. A successful rose grower never places a 10-dollar plant in a 2-dollar hole.

Mulching

Mulched rose plants have several advantages over those grown in bare soil. Mulching prevents soil crusting and erosion, maintains a uniform soil temperature, conserves moisture and reduces weeds.

Mulching materials include fall leaves, pine straw, ground pine bark and hardwood chips. Your choice depends on cost, availability and ease of handling. A 2- to 3-inch layer of mulching material is adequate. Too much mulch causes soil to retain excessive moisture.

Watering

Adequate soil moisture is essential for rapid, healthy cane growth and flower development. During dry weather, water mulched roses at least once a week. Unmulched plantings require more frequent watering. Three to five gallons of water per plant at each watering should adequately wet the root zone.

Avoid using lawn sprinklers or other overhead irrigation devices that wet the foliage and encourage leaf diseases. A soil-soaker hose placed under the mulch is ideal for watering roses. Drip or trickle irrigation kits are also excellent irrigation systems for rose plantings.

Fertilizing

Fertilization varies widely, depending on plant size, soil type, rainfall and the time of growing season. Many rose growers have developed their own recipe for fertilization based on past experience or the experiences of others. This has led to many different approaches to rose fertilization.

Light fertilizer application at monthly intervals are recommended. A 12 to 16 percent nitrogen source such as 16-4-8 or 12-4-8 fertilizer is advisable. Three tablespoons per plant per application is usually adequate. If the plant is shorter than 1 foot, reduce the rate to 1 tablespoon. Large bushes, 6 feet tall, respond to 5 tablespoons per application. Beginning 6 inches from the main stem, spread the fertilizer evenly in a circle around the shrub. Use a rake to mix it lightly into the soil and water soon after application. Avoid getting fertilizer on the foliage, canes or flowers and too close to the main trunk.

Pruning and Grooming

Roses respond to pruning and grooming (removal of old flowers) by producing specimen flowers in greater quantity. Larger, more attractive flowers are the result of well-groomed, correctly pruned plants. Major pruning is done in early spring (before growth begins) while grooming is done throughout the growing season.

All plants are not pruned alike because of differences in flowering and growth habits. Generally, weak-growing varieties are pruned lightly while vigorous growing varieties are pruned more heavily and more frequently. In either case, wounded or weak canes or those showing evidence of bark splitting should be removed first.

Here are specific instructions for pruning the various types of roses:

Hybrid Teas — Hybrid teas (garden type or cut-flower roses) should be pruned in early spring just before new growth starts. Leave at least four to six of the most vigorous canes. Prune these canes back to within 24 to 30 inches of ground level. Make the cuts about ¼ inch above a bud. Always use clean, sharp pruning shears (Figure 5).

Figure 5. Keep all spinkly growth removed. When spring growth begins, remove all but four or six of the healthiest canes. Cut the remaining canes one-half their length.

Vigorous shoots (suckers) originating below the graft union will be different in foliage and flower from the desired grafted variety and should be removed. If allowed to develop, they will compete heavily with the grafted variety.

Groom the plants by removing old flowers as soon as they have passed their peak. If allowed to remain on the plant, the flower heads will develop seed pods (also called hips) that draw heavily on the plant’s food supply. Also, remove any spindly shoots or sucker originating from below the graft union or any stems showing disease symptoms during the growing season.

To produce specimen flowers on hybrid tea or garden roses, remove the flower buds that develop on shoots other than the main one. Allow only one flower bud to develop and mature on each main shoot (Figure 6).

Figuire 6. For larger, quality blooms for exhibition or show purposes, always remove all but one bud per stem. Pinch or prune the extra buds while they are young and soft.

Climbing Roses — Climbing roses require special pruning for profuse flowering. Many varieties in this group produce most of their flowers in the spring. During flowering, they will develop new canes on which next year’s flowers will be borne. Prune to remove the oldest canes near ground level immediately after flowering to promote vigorous new shoot development.

Prune climbers to keep them trained to their support (fence, trellis, wires). Climbers generally require much less pruning than do other types.

Some climbers bloom off and on during the spring and summer. However, they usually have a peak flowering period quite early in the season. Prune these climbers following their first flush of flowering (Figure 7).

Figure 7. Prune climbers after the first flush of flowers. Keep weak, diseased or dead stems removed. Leave five or six healthy, vigorous canes. Thick, dense growth of climbers leads to problems.

Canes of most climbers are good flower producers for two years. In some cases, new canes develop only on the older canes rather than from ground level. In such cases, remove the oldest canes in early spring, leaving five or six of the healthy, vigorous ones. Also, keep all faded flowers cut from the plants.

You can now get climbing forms of many hybrid tea varieties, which are generally more vigorous than their corresponding bush varieties. Prune them in early spring to remove weak, spindly growth and dead or diseased branches.

Floribundas and Grandifloras — Floribundas and Grandifloras are grouped together for practical purposes. Both produce flowers in profusion. Floribundas have a shrub growth habit and are low- to medium-growing. Consequently, pruning is generally confined to maintaining plant shape and vigor. Grandifloras have a growth habit similar to that of hybrid teas and are pruned in the same manner.

Cutting Roses

Cut roses in early morning or late afternoon when there is more stored food in the stems and flowers. Stored food lengthens the life of the cut flower. Make cuts about ¼ inch above a node and cut only the length of stem needed for the flower arrangement.

Put the cut stems in water as soon as possible. Have a bucket or container with you in which to place each stem as it is cut. Put the bucket of cut roses in a cool, dark place for several hours. If room permits, place them in the lower part of your refrigerator. Unopened flower buds can be stored in the refrigerator for several days until blooms are desired for special occasions.

Controlling Pests

Roses will not be productive during the flowering periods unless they are kept free of insects and diseases. It is important to understand the characteristics and the types of damage caused by insects and diseases.

Before applying any pesticide, always read and follow the instructions on the label. Play it safe! Do not expose yourself or your plants to unnecessary hazards such as improper measuring, mixing and application of insecticides and fungicides.

Careful observation of your plants throughout the year is of utmost importance. This allows early detection of problems that may arise and leads to better control, better plants and greater personal satisfaction.

Successful rose growers prevent problems more often than they control them. Here are a few tips that will help keep your plants beautiful, vigorous and productive:

Buy healthy plants. Avoid those with any abnormal swellings or discoloration on canes or roots. Do not, however, confuse the enlarged graft union with a disease.
When applying fungicides, always spray the area underneath the plant where leaves have fallen. This will help in your disease control program.
Cut out any canes showing cankers, discolorations or sunken areas. Make cuts 4 to 6 inches below the infected area. Before making each cut, dip shears in a solution of rubbing alcohol or a solution of 9 parts water and 1 part bleach. Destroy all infected stems, leaves and faded blooms.
Remove and destroy any plant infected with crown gall or root-knot nematodes. Do not replant on such sites if at all possible.
Successful rose growers follow a regular spray program. Generally, each application contains a fungicide for disease control and an insecticide for insect and mite control. Applications are usually made at weekly intervals or as indicated on the pesticide label. Preventive spraying is the most effective approach to controlling pests.

Leaf diseases are extremely difficult to control once they have become established. When applying fungicides, cover the surfaces of stems, leaves, flower buds and canes thoroughly to adequately control pests. Do not delay spraying even if rain is forecast. Most disease-causing organisms require this wet environment to infect; this is the time fungicides are needed the most.

Diseases

Black spot is the most prevalent rose disease. It is characterized by circular black spots with irregular margins on leaves. Control with fungicides is difficult. Mulching around plants can reduce disease occurrence. The leaf spots may increase in size and number with time. Infection will cause leaves to turn yellow and drop. Severely infected plants may be completely defoliated by midsummer.

Black spot disease is unsightly. More importantly, the disease reduces leaf function, which weakens the entire plant. The result is a plant that grows very slowly and is more susceptible to other diseases and winter injury.

Figure 8. Black spot disease causes discoloration and leaf drop.

Powdery mildew is a rose disease that stunts and distorts young, tender growth of buds, leaves and canes. Older leaves may also be diseased, but damage is not as severe. The fungus is a prolific spore producer. These spores form on the surface of the tissue, which gives it a “powdered” appearance — hence, its name. Fungicide application to new growth can reduce disease incidence and spread. Disease development requires damp, cool nights, which can occur any time during the growing season. Some varieties of climbing roses and small-flowering ramblers are most susceptible to this disease.

Figure 9. Mildew is severe on stems, buds and leaves during damp, cool weather.

Botrytis blossom blight is severe on some varieties of hybrid teas, particularly the whites and pinks. This disease affects the buds and partially opened flowers. It is recognized by its grayish-brown fungus growth on the buds and petals under humid, wet conditions. The fungus overwinters on infected plant parts, especially winter-killed stems. Pick off and destroy faded and infected blooms. Fungicides are effective in controlling the disease.

Crown gall, caused by a soil-borne bacterium, severely damages roses. The bacterium usually gains entry into the plant via wounds or natural openings. This disease causes large, corky growths or galls to form on the crown or roots. Sometimes galls develop on above-ground portions of the plant. These galls first appear as small swellings that slowly increase in size. Diseased plants show a loss in vigor and produce smaller blossoms and leaves. This effect on the plant becomes evident only when the galls have reached a diameter of several inches. Do not confuse crown gall with normal enlargement of the graft union of plants (Figure 10). Infection may occur during grafting; therefore, inspect nursery stock before buying. Burn or destroy all infected plants. Chemical control of this disease is not effective.

Figure 10. The large, dark- to flesh-colored gall shown above is characteristic of Crown Gall disease. Galls can also occur on shallow roots.

Stem cankers. The three most common stem canker diseases are caused by fungi that invade the plant through wounds caused by pruning, cultivation or winter injury. Hybrid tea varieties are more susceptible than others. Failure to control leaf diseases with fungicides increases susceptibility to stem cankers.

The fungi overwinter in cankers and continue to spread during the season. If left untreated, the infection can girdle the cane, causing death or poor growth above these infected areas. (Figure 11)

Figure 11. Symptoms of stem canker. Notice the difference between the dark, infected tissue and the lighter, healthy tissue.

To control stem canker infections, prune and discard all infected tissues. Be sure to make cuts well below the blighted areas. Disinfect pruning shears between cuts with a surface disinfectant such as isopropyl rubbing alcohol.

Viral Diseases

There are several viral diseases of roses. Most of these maladies are transmitted to non-infected plants through vegetative propagation processes used by commercial rose producers or through pruning. There is some evidence that at least two of these viral diseases are transmitted to other plants by insects or spider mites. Viral infected roses tend to be less vigorous, are more susceptible to other diseases, and are less likely to tolerate environmental stresses as healthy plants do.

There are at least six known viral diseases of roses. Yellow and green mosaic patterns, leaf distortion and ring spots are possible symptoms of virus infections. (Figure 12) Others that exhibit viral-like symptoms have not been linked to a particular virus. It is not unusual to encounter plants infected with more than one virus. Also, such occurrences usually cause problems in positive identification.

Figure 12. Typical viral symptoms on rose.

Some chemical toxicities and nutrient deficiencies express symptoms similar to those caused by viral diseases. Removing severely infected plants may be the only solution. Preventive measures to prohibit the spread of viruses include disinfecting pruning shears when moving from one plant to another, and a good insect control program is a must. Also, buy plants that are apparently healthy and exhibit no peculiar foliar symptoms (Figure 13).

Figure 13. Symptoms of the rosette virus. Note the increased numbers of thorns; clusters of deformed, crinkled leaves; and the many small leaves originating from one point (a condition called “witches’ broom”). Symptoms sometimes mimic those associated with herbicide injury.

Insects and Mites

Aphids. Several species of aphids damage roses by removing large quantities of plant juices and by secreting a sticky substance over the surface of infested plant parts. Heavy infestation can cause abnormal growth of plants.

Aphids are small, approximately ? inch long, and vary in color from yellow to green to black. Their life cycle is completed in as few as four days under favorable environmental conditions. Remove and destroy heavily infested plant parts. Then treat plants with an insecticide registered for aphid control on roses. Inspect roses for aphids two to three days after application. Due to their short life cycle, aphids can rapidly build back up in number; therefore, several applications of insecticide may be necessary to bring the population under control.

Thrips. Thrips are another troublesome pest on roses. Thrips enter developing flower buds to feed and cause petals to become flecked and discolored. Heavy infestations cause deformities in new growth and can be responsible for buds not opening properly. Adult thrips are tiny, slender, brown to yellow insects with feather-like wings. They are most easily seen by shaking new growth or flower buds over a white cloth.

Thrips have repeated generations during spring through fall. In hot, dry weather they complete a life cycle in less than two weeks. Cutting off and disposing of old blooms lessens infestation. Do not leave old blooms on the ground or thrips will quickly leave them and reinfest plants. Treat infested plants with an insecticide registered for thrips control on roses. Complete coverage of infested plants with the insecticide is important to your control program.

Spider Mites. Mites are such small pests that they often cause damage before they are noticed. Mites are found on the underside of leaves, there they feed by sucking plant juices. Infested leaves will have many tiny chlorotic spots. Heavy infestations cause leaves to turn brown and die.

Mites have a very rapid life cycle and can complete development in less than a week under hot, dry conditions. A control program for mites begins with the removal of weeds and other plants serving as alternate hosts for mites. Frequently inspect roses for the presence of mites. A magnifying glass is useful for seeing mites. When mites are found, treat plants with a registered miticide and reinspect plants for mites three to four days later.

Other Insect Pests. Rose chafers, scale insects and Japanese beetles are occasionally found damaging roses. Rose chafers are buff-colored beetles ½ inch long with long, spiny legs. They feed on the rose blossoms. Japanese beetles are bright green, about ? inch long; they feed on the foliage (Figure 14). Scale insects are small, stationary insects found on the stems and leaves of roses. They damage roses by removing plant juices with their sucking mouth parts.

Figure 14. Japanese beetle feeding injury on rose petals.

Nematodes. Nematodes are microscopic worms that feed on plant roots. They may stunt young rose plants and can cause a slow decline in older ones. If you suspect nematodes have entered your rose bed, take a soil sample from the root zone of the plants involved. Place a pint of this soil in a plastic bag. Be sure the soil is moist. Take this sample to your county extension agent, who will have the soil examined for nematodes.

source: pubs.caes.uga.edu, photo from cherryvalleynursery.com

For more info, contact:

Dept.of Agriculture
D.A. Compound, Elliptical Rd.,
Diliman,Quezon City
Tel. Nos. (632) 929-6065 to 67 / 920-3991 / 928-1134
Web: www.da.gov.ph