Technique for Rapidly Cultivating Ball-and-Stem Shaped Nursery Stock of Large-leaf Euonymus through Long-branch Cuttings
Large-leaf euonymus, also known as evergreen euonymus, is an evergreen shrub or small tree of the Celastraceae family. It generally grows 60-90 cm tall, and can reach up to 3 m. Large-leaf euonymus has dense branches and leaves, glossy young foliage, stays green through all four seasons, and is fresh and elegant, making it much loved as a common foliage ornamental plant. Large-leaf euonymus is native to Japan, and is now widely cultivated across the northern and southern provinces of China. It likes light and tolerates shade, and is suited to growing in warm, humid climates and loose, fertile sandy loam; it is also fairly cold-tolerant, and except for non-lignified new shoots sometimes suffering frost damage in winter, it can generally overwinter safely even when planted in the open in northern regions.
Large-leaf euonymus is suitable for planting in flower beds, hedges, in front of courtyards, beside steps, or for accenting lawns and roadsides. Grown as a potted ornamental, it can also give people a calm and soothing pleasure. Because of its strong sprouting ability, it is extremely tolerant of pruning and shaping. In landscaping, it is often pruned as needed into various shapes such as wavy, spherical and square forms to accent lawns or form color blocks. The ball-and-stem shape is a relatively novel form among large-leaf euonymus topiary styles; it is a shaping method in which the part of the large-leaf euonymus above ground at a height of 50 cm is kept free of branches and leaves and trained into a trunk, while the branches and leaves above 50 cm are pruned into a sphere.
In nursery stock production, ball-and-stem shaped large-leaf euonymus is generally cultivated by using Euonymus bungeanus as the rootstock, large-leaf euonymus as the scion, and grafting. This method requires pre-cultivating the rootstock, and only after the graft survives can further pruning and shaping be carried out, so it requires a relatively long cultivation time. However, through long-branch cuttings and pruning and shaping of large-leaf euonymus, the grafting step can be omitted, cultivation time shortened, survival rate increased, and ball-and-stem shaped large-leaf euonymus rapidly cultivated.
1 Techniques for long-branch cutting of large-leaf euonymus
1.1 Land preparation and bed making
Select a flat, wind-sheltered, sunny site near a water source and easy to drain and irrigate as the cutting site, and make it into a low bed 1200 cm wide and of indefinite length. To facilitate field operations, a walkway of 50-80 cm may be reserved. Take yellow soil free of pest and disease infection, sieve it, and mix in 1/4 clean river sand (particle size 0.25-0.5 mm), mixing the soil and sand evenly as the cutting substrate. Loose sandy soil, peat soil, vermiculite, perlite and other seedbed substrates may also be chosen, and fine river sand, garden soil and rice-hull ash may also be mixed in a 1:1:1 ratio as a mixed cutting substrate. Whichever cutting substrate is used, it must be loose, breathable and well-draining, so as to avoid insufficient oxygen supply affecting the growth of adventitious roots. Fill the prepared cutting substrate into the cutting bed, striving for a level bed surface; the bed surface should be 20 cm lower than the walkway. After leveling the bed surface, disinfect the substrate with a 3% ferrous sulfate solution, using 0.5 kg of solution per sq m. Then use a watering can to evenly spray clean water onto the substrate; after adding water the substrate should not be too wet, and just able to form a ball when held in the hand is best.
1.2 Cutting and treatment of cuttings
In mid-to-late June, select vigorous, pest- and disease-free, semi-lignified one-year-old branches more than 30 cm long as cutting wood, cut the branches before 9 a.m., and promptly cut the collected branches in a shaded place into 50 cm long cuttings. Cut the lower part of the cutting near a node into a horseshoe shape with an inclination angle of 40°-45°, and make a flat cut at the top, with the cut 1-1.5 cm from the first leaf above, keeping the cut smooth and not tearing the stem bark or damaging the axillary buds. Leave 3-5 pairs of leaves on the upper part of the cutting, and remove all lower leaves. Bind every 50 prepared cuttings into a bundle, align the lower cuts neatly, and tie them for later use. Dissolve 1 g of ABT rooting powder in 10 kg of water, immerse the lower 3 cm of the cuttings in it, take them out after 0.5 min and set aside for insertion.
1.3 Cutting insertion
1-2 h before insertion, use a watering can to evenly spray clean water onto the cutting substrate and water the cutting bed thoroughly, then insert the cuttings at a spacing of 10 cm × 10 cm. An insertion depth of 6-8 cm is suitable. Before insertion, a small wooden stick of a thickness similar to the cuttings may be used to first make insertion holes in the substrate, then insert the cuttings into the holes, and afterward press lightly around the holes with the fingers. After inserting, spray clean water once more to wash the leaves and make the cuttings closely combine with the substrate.
1.4 Shading
To prevent strong light exposure, after insertion insert bamboo arches on the bed to build a small arched shed, with the shed top about 100 cm from the bed surface, and cover the bamboo arches with a shade net to shade the cuttings, keep the seedbed moist, and help the cutting wounds heal and root.
2 Factors affecting the survival of long-branch cuttings of large-leaf euonymus
2.1 Age of the mother tree from which cuttings are collected
According to experiments, the older the mother tree, the less easily the collected branches root. Branches collected from 1-2a-old mother trees have a rooting survival rate as high as over 95%, while for mother trees grown for more than 3a, the rooting survival rate of collected branches is below 90%.
2.2 Age of the cutting branches
According to experiments, for branches used for cuttings, 1-2a-old branches have a relatively high cutting survival rate. In particular, vigorous one-year-old branches sprouting from near the root have the highest cutting survival rate.
2.3 Plumpness of the branches
Experiments show that the plumper the branches used for cuttings, the higher the cutting survival rate. For long-branch cutting of large-leaf euonymus, one-year-old plump and vigorous branches should be selected as cuttings. In particular, branches sprouting from the root are best, with relatively high plumpness and cutting survival rate.
2.4 Temperature
Cutting of large-leaf euonymus can be carried out in all three seasons of spring, summer and autumn, but cuttings taken in mid-to-late June root quickly and grow well. For spring hardwood cuttings, 15°C-20°C is suitable, while for summer softwood cuttings, the temperature is usually about 25°C. Experiments show that for long-branch cutting of large-leaf euonymus, maintaining a temperature of 20°C-25°C makes rooting and survival easiest.
2.5 Humidity
After cutting, suitable moisture helps large-leaf euonymus root, so in addition to maintaining a certain humidity in the substrate, the relative humidity in the air must also be controlled; especially for summer softwood cuttings, high air humidity is required, with relative air humidity above 90%, to keep the cuttings from withering. When the sunlight is strong at noon, the cutting seedbed needs to be shaded with reed curtains or a shade net. Generally, rooting occurs about one month after cutting; as the root mass of the cuttings increases, the shading material should be gradually removed, light increased, and air humidity and substrate humidity reduced, which helps promote root growth and cultivate strong seedlings.
2.6 Light
For summer softwood cutting of large-leaf euonymus, a certain amount of light is needed for rooting and survival. Sufficient light can promote the leaves to produce photosynthetic products and promote rooting of the cuttings, especially in the later stage of cutting; after the cuttings root, light conditions are even more needed. However, in the early stage of cutting, care must be taken to avoid direct strong light, to prevent excessive evaporation of water from the cuttings, causing leaf wilting or scorching and affecting root initiation and root growth. Therefore, shading should be strict in the early stage of cutting; after callus tissue forms, light should be gradually increased. In mid-November, when the temperature is below 10°C, the shading material should be gradually removed and covered with plastic film, with the edges pressed down with soil to prevent cold.
3 Post-cutting management
3.1 Control of temperature and humidity
After cutting, water should be sprayed frequently to keep the substrate moist; when sunlight is strong, the seedbed should be shaded to avoid strong light exposure, keeping the temperature inside the shed at 20°C-30°C and relative humidity above 90%. After about one month of management, the cuttings begin to root.
3.2 Appropriate fertilization
After the cutting seedlings grow 3-4 new leaves, their resistance gradually increases, and some organic fertilizer can be applied. The method is to use 1 part cake fertilizer and 10 parts water, place them in a tank and let them fully decompose. When using, take 1 part of decomposed cake fertilizer water and mix with 10 parts clean water, and water it on with a watering can, applying once every 15-20d. Apply frequently and thinly, and prefer dilute over concentrated.
3.3 Pest and disease control
The main diseases of large-leaf euonymus in winter are cloud-pattern twig blight, anthracnose and brown leaf spot, which can be prevented and controlled by spraying with 800-fold chlorothalonil solution or 1000-fold fungicide solution. Bud blight, root rot, anthracnose and the like that easily occur in spring can be prevented and controlled by spraying with 70% thiophanate-methyl 1000-fold solution or 50% carbendazim 800-fold solution. The main insect pests of large-leaf euonymus are long scale insects, flat sting moths and euonymus spotted moths, which harm the leaves and should be controlled with attention. Cutting seedlings in the shed are prone to scale insect damage, which can be controlled with 20-fold rosin mixture; for flat sting moths and euonymus spotted moths, use 40% omethoate or isocarbophos 1000-fold solution at the larval stage.
3.4 Timely transplanting
Large-leaf euonymus that survives cutting can be transplanted in the spring of the following year. When transplanting, the roots of the seedlings should be dipped in mud slurry to increase the transplanting survival rate. Considering the needs of shaping, the plant spacing should be appropriately increased. After transplanting, tread the soil firm and water thoroughly.
3.5 Pruning and shaping
In cultivating ball-and-stem type large-leaf euonymus, the most important thing is timely bud removal. After the cuttings survive, buds should be removed promptly to maintain apical dominance; when the branches grow to 50 cm, the tips should be pinched promptly to promote side branches. Thereafter, as the branches grow, no branches or leaves are kept at 50 cm above ground, and new shoots above 50 cm should be pruned promptly to promote the sprouting of new branches. After pruning, the branches of large-leaf euonymus sprout very easily, so after the cutting seedlings survive they need repeated pruning, and the sprouted branches should be reasonably selected and removed to maintain a certain tree shape. In mid-November, plastic film should be added to resist cold wind, and in the early spring of the second year pruning should be carried out again; through pruning the whole plant is shaped, and through repeated pruning and shaping it can be cultivated into a ball-and-stem shaped large-leaf euonymus with a distinctive trunk and branches.