Agdex No. 276.21

Shrub roses can provide an attractive, easy care alternative to hybrid tea or floribunda roses. They can be used in a wide variety of ways; in foundation plantings, specimen plantings, informal screens or shrub borders. Shrub roses produce an abundance of flowers and fragrance during the growing season. Many also have decorative foliage and produce attractive fruit for winter colour.

Shrub roses prefer full sun and good air circulation but otherwise are easy care shrubs that usually do not require winter protection.

Shrub roses prefer a good clay loam soil but will grow well in lighter soils where organic matter is added. Organic matter improves soil structure and water retention. Well rotted manure is recommended, but peat moss and compost are beneficial organic amendments. If peat is used, it is recommended that fertilizer be mixed with the peat at the rate of 1 kg of 5-10-10 or 5-10-15 to 1m3 of peat. 1m3 of organic matter is sufficient for about 10m2 of bed. Roses grow best in soils of pH 6.0-6.5. If the soil is acidic (pH less than 6.5), add lime at a rate of 2 kg/m2 for every unit of pH up to pH 6.0. A soil test available through the N.B. Dept. of Agriculture will give specific fertilizer and lime recommendations.

Shrub roses require plenty of moisture to assure steady growth, but they do not like poorly drained soils. If the subsoil is heavy clay, open it with deep digging and where possible, drainage tiles. Sandy soils may require an addition of organic matter to increase water holding capacity.

Roses usually do not require supplemental watering. However, during dry summers, roses should be watered at least every 10 days if there has not been enough rain to soak to a depth of 25 cm. When watering roses, avoid wetting foliage as it encourages disease infestation.

The preferred time to plant is in the spring while the roses are still dormant.

For planting later in the spring, potted roses are useful. Beds should be prepared the previous fall so planting can be done as early as possible and to allow the freezing and thawing action throughout the winter to improve soil structure.

For best results, roses with 3 or more strong canes should be purchased.

Packaged roses should be purchased soon after they appear on the market, just prior to budbreak, as once the buds start growing the plants are difficult to establish.

Plant packaged shrub roses soon after purchase. If planting is to be delayed, leave roses packaged and store in a cool place. Keep the roots of packaged roses moist at all times before and during planting. If roots are dry, immerse them in a tub of water for several hours before planting and thoroughly soak potted roses before planting.

Shrub roses should be planted 1m apart for smaller varieties and 2m apart for larger varieties.

Prior to planting examine rose bushes carefully. Remove any broken roots by cutting them off cleanly above the break and trim off dried roots. All weak top growth and broken canes should be pruned off to leave the strongest canes.

For packing purposes, rose roots are often curled; these should be separated and spread naturally when planting. Dig a hole large enough to hold the root without crowding and deep enough so that when planted the bud union on the shrub is covered by about 2.5 cm of soil.

It is helpful to make a cone shaped mound in the center of the hole using the soil mix prepared for the bed. Place the rose bush on this mound making sure the bud union is below ground level and roots are well spread out. Fill hole with soil mix and tread in firmly, to eliminate air pockets. Water thoroughly and make a shallow dish around planting hole. This will help to capture extra moisture until the plant is established.

Shrub roses generally need little pruning. If required, cut out a few old branches each spring from the established plant as this encourages new shoots to form at the base of the shrub. The weakest of these new shoots can be thinned out later. Certain varieties require cutting the shrub back one quarter of its growth. This encourages the production of new shoots which will arise from old canes and produce most of the blooms for the current year.

The fertilizer incorporated into the beds during their preparation should be sufficient for the first year. Well rotted manure can be used to add nutrients as well as organic matter but shrub roses should not be fed with high nitrogen or fresh manures.

Specially formulated rose fertilizers used as directed are effective. Fertilizer should be applied in the spring when new growth has commenced and then repeated in July after the first flush of flowers.

Most shrub roses will overwinter reasonably well if the plants are hardened off correctly. In N.B. no fertilizing should be done after mid-July to avoid stimulating tender new growth in the fall. Late fertilization does not allow a plant to harden off adequately and prepare for cold winters.

Shrub roses can be mulched to help retain soil moisture and control weeds in the beds. Suitable materials for use as mulch include: bark chips, wood chips, and sawdust. Landscape fabric, a permeable synthetic material can be applied under the mulch to provide a good long term control against weeds.

Shrub roses are often subject to two common diseases, mildew and blackspot.

• Mildew forms a greyish cobwebby covering on leaves. It occurs most often in moist weather when there is poor air circulation. To control the disease remove and destroy infected plant parts when affected area is small and use proper pruning and spacing to increase air circulation.

• Black spot causes black spots with yellow halos on the leaves. It often leads to early loss of leaves. The disease overwinters on the fallen foliage and stem spots so it is necessary to practice good sanitation. Collect and dispose of all leaf litter and prune any infected plant stems.

The most common insect problems of shrub roses are caused by 2 main types of insects:

1. sucking insects that have mouth parts that penetrate the surface tissue of leaves and stems and suck juices from them (e.g. green aphids),
2. chewing insects which eat the leaves (e.g. caterpillars and beetles).

Cultural methods can provide good control of most rose insects and diseases. Avoid problems by selecting roses with natural resistance to diseases and insects. Practice good sanitation and consider air circulation when planting to reduce disease infestation.

If pest problems persist, there are chemical controls available for roses at your local garden centre or nursery, or consult the N.B. Department of Agriculture.

For information on shrub rose varieties, consult N.B. Department of Agriculture Publication 'Hardy Shrub Roses for New Brunswick'.