A Complete Analysis of the Key Cultivation Techniques for Roses
The rose (Rosa chinensis) is a deciduous plant native to temperate zones and has a certain degree of cold tolerance. When planted in most areas of northern China, it requires mounding soil over the base to protect it through winter; in other areas, it can overwinter naturally in the open ground. It prefers sunlight and has no strict requirements for day length, so it can bloom continuously. In midsummer it mostly stops growing and produces few flowers. If brought into a high-temperature greenhouse in winter, it remains evergreen and continues to bloom, but this is detrimental to the following year's growth. It is not demanding about soil, preferring neutral, well-drained loam and clay loam, and can tolerate mild alkalinity. It grows poorly in sandy and acidic soils. It has a high fertilizer requirement, and fertilizer must be applied regularly for it to keep blooming.
Propagation Methods for Roses
Rose propagation is mainly vegetative, and can be done by cuttings, grafting, division, and layering, with cuttings and grafting being the most commonly used.
1. Propagation by Cuttings
For rose propagation by cuttings, the first step is to prepare a heated cutting bed. Fermenting material such as horse manure or leaves should be placed in the bed, watered, and pressed down firmly, all of which will generate a certain amount of heat. From the mother rose plant, cut semi-lignified branches after the flowers have faded, about 10 cm in length, generally with three bud eyes per branch. All the leaves on the lower part of the cutting should be removed, leaving only the two leaves at the tip for photosynthesis. Too many leaves should not be retained, as they consume nutrients stored in the stem and evaporate a large amount of water. Cut the base of the cutting into a "horseshoe" slant shape and place it in a basin of clean water to prevent air-drying; it should be planted promptly. The most suitable temperature for rose rooting is 20-25 degC, and rooting generally begins only above 8 degC. If the winter ground temperature is below 8 degC, rooting after cutting is very difficult. When the spring temperature rises, besides paying attention to spraying the bed surface, the moisture in the bed must not be neglected; otherwise, due to lack of water, the cuttings will wither, and even small seedlings that have already rooted will dry out and die. To check the substrate, insert your hand 8-10 cm deep into the soil and take out a small amount; if it can be pressed into a ball by hand, the moisture is suitable; if it cannot be pressed into a ball, the soil is short of water. First use a wooden stick to make a hole, then insert the cutting into the sand hole and press it firm by hand. The insertion depth should be 1/3 of the cutting's length, and the spacing should be such that the leaves do not overlap. After inserting, promptly water with a fine watering can until thoroughly soaked. After firming the bed sand, cover it with plastic film and shade it for 1 week, spraying the leaves 1-2 times per day. After about 1 week the wound begins to heal, and after about one month roots form and it can be transplanted. When transplanting, the roots should be coated with mud slurry, and planting should be done as they are dug out. Mixing 1%-2% copper sulfate and about 0.50% urea into the mud slurry can both prevent root rot and promote seedling growth and survival. Before potting, place broken tile pieces over the drainage hole of the flower pot, add mixed soil, then plant the seedling with its soil ball into the pot, adding soil in layers and pressing firm. After planting, water thoroughly once, place in a shaded shed for 7-10 days, then move to a ventilated, sunny spot. After potting, water thoroughly once a day.
2. Propagation by Grafting
Grafting is the main means of propagating roses. When grafting, the choice of rootstock is very important. The rootstock should have an ample source of cuttings, root easily, adapt to local climatic conditions, and have good affinity with the scion. At present, the rootstock commonly used in China is rose (Rosa multiflora). Dormant-season grafting usually uses whip grafting, before the leaf buds break in spring. Growing-season grafting usually uses bud grafting.
Cultivation and Management of Roses
Rose cultivation is divided into protected cultivation and open-field cultivation.
1. Protected Cultivation (Pot Cultivation)
The rose is a sun-loving plant, but overly strong light is detrimental to flower bud development, while growing in insufficient sunlight makes the branches slender. It takes about 45 days from bud break to flowering. The optimum temperature for growth is 15-25 degC; within this temperature range the flowers are large and beautiful. At 30 degC growth slows, and above 30 degC the flowers become smaller and the flower color fades. When potting 2-3-year-old plants, the roots should be trimmed, cutting the old roots short to encourage new root growth, but root trimming should not be too severe. When planting, make sure the root system is spread out and the plant is upright, and the pot soil should not be filled to the brim. Potting is generally done during the dormant period. Roses grow vigorously and need much fertilizer, so repot once a year or once every other year, during the dormant period, and water thoroughly twice after repotting. In spring, summer, and autumn, they should be placed in a spot with ample sunlight, good ventilation, and no water accumulation. After Qingming (early April), this is the time for a careful pruning when the roses come out of the cellar. Select and retain the robust branches of the rose, and cut off all the others: horizontal branches, weak branches, crossing branches, and overly dense branches. The retained branches should have 3-5 bud eyes kept from the base, and all growth above that should be cut off, so that the plant absorbs a large amount of nutrients from the soil to supply the long-term growth needs of the leaf buds and flower buds on the retained branches. Remember not to prune after the buds have broken; late pruning affects the first flowering. Growth height should be kept uniform. Each plant can retain 3-5 main branches, at most 7. Do not water potted roses unless the soil is dry; when watering, water thoroughly. In summer, the weather is hot and evaporation is high, so potted plants should be watered more, especially the evening watering, which should be sufficient. When the temperature exceeds 30 degC, roses grow poorly and bloom less. Some people think this is due to insufficient fertility and apply more topdressing, which actually makes things worse. In midsummer, topdressing is generally not applied; only for robustly growing plants, apply light fertilizer frequently, 1-2 times per week. If possible, provide proper shading after 11 a.m. and let them get sun again after 4 p.m., avoiding the hot midday temperatures while allowing them to receive the weaker sunlight before and after noon, which is beneficial for photosynthesis and accumulates nutrients for the next flush of flowers. Fertilizer can be applied right after pruning, using 50% human waste mixed with 2% superphosphate. In mid-February, apply topdressing with 3% human waste or 1% urea. Urea can also be applied before or after rain. Do not fertilize when new shoots are red; fertilizing at this time injures the young roots, causing the plant to wilt or stop growing, so special attention must be paid to this. Roses also require mid-season pruning, mainly to remove the sprouting shoots from the rootstock of grafted plants, to cut off spent flowers along with leaves after flowering, and to thin out excess flower buds. After the first flush of flowers, cut the slender, weak flower branches from the base; for the remaining thick, strong flower branches, cut just below the 2-3 leaves beneath the spent flower. For the second flush of flowers, the method of thinning weak branches, retaining strong branches, and keeping strong buds can still be used. Roses also require one pruning before overwintering, but not too early. When pruning roses, not only should strong branches be selected and retained, but attention should also be paid to even distribution of main and secondary branches. For large-flowered cultivars, retain 4-6 strong branches, and on each branch select a strong lateral bud at 30-40 cm, cutting off the upper and middle portions of the branch. For trailing and climbing cultivars, remove old branches, weak branches, and diseased and pest-damaged branches to train the main trunk.
2. Open-Field Cultivation
Roses planted in the open field have well-developed root systems, grow rapidly, are robust, bear slightly larger flowers, and have high ornamental value. In management, cultivation measures should be chosen according to different types, growth habits, and geographical conditions. Choose a planting site with higher terrain, ample sunlight, air circulation, and slightly acidic soil. When planting, plow the soil deeply and apply organic fertilizer as a base fertilizer. For upright cultivars, the planting density is 75 cm x 75 cm; for spreading cultivars, the plant and row spacing is 100 cm x 100 cm; for columnar cultivars, the plant and row spacing is 40 cm x 50 cm; for climbing cultivars, the plant and row spacing is 200 cm x 200 cm.
Pest and Disease Control for Roses
1. Chemical Control
(1) Powdery Mildew
A fungal disease that harms flowers in environments with high temperature, poor ventilation, and relatively high humidity. A white powdery appearance on young leaves is called powdery mildew. It can be treated with a 600-fold dilution of triadimefon or a 400-fold dilution of Tuzet.
(2) Black Spot
Caused by fungi, it overwinters in the soil on diseased residual branches or fallen leaves as mycelium or acervuli. In the following spring, it absorbs water and produces conidia, which are mainly spread by wind and rain. Rainy, foggy, and dewy weather favors spore germination, so the disease occurs easily. When water droplets are present on the leaves, the spores can germinate and invade within 6 hours. Under conditions of high air humidity during the rainy season, the pathogen reproduces readily and the disease becomes epidemic. A 0.10-0.20 Baume lime sulfur mixture, or a 50% carbendazim wettable powder 500-1000-fold dilution, can be sprayed on the leaf surface.
2. Integrated Control
The pathogen should be eliminated early. In early spring, in the first ten days of April, after the roses come out of the cellar and before the trees become active, prune once first. Before budding, spray the roses comprehensively and carefully (including the plant, pot soil, and the ground around the pot) with a 0.50-1 degree Baume lime sulfur mixture. For regular chemical control of the plants, a 75% wettable chlorothalonil 500-fold dilution and an 18% copper fungicide 150-fold dilution can be sprayed once every 10 days. If it rains after spraying, spray again promptly after the rain. The spraying period is from June to September, with frequent spraying to control the occurrence of black spot.