How to Prune a Plum Tree? A Detailed Guide to Planting and Pruning Methods
I remember when I was a child, there were several plum trees in front of our house. Every year when the plum trees bloomed, they were especially beautiful. But with the continuous development of the rural economy today, the plum trees in front of our house are long gone, and now many fruit grower friends have started planting fruit trees in large areas.
The Role and Timing of Pruning
Pruning can regulate the relationship between growth and fruiting in fruit trees, maintain a strong capacity for growth and fruiting, and keep yields stable. Pruning of plum trees is divided into summer pruning and winter pruning. Summer pruning is carried out during the growing season, so it is also called growing-season pruning. Generally, it can be done 3~5 times:
The 1st time is after spring bud break, mainly to remove buds in improper positions and the weak buds among double buds, reducing ineffective branches and saving nutrients;
The 2nd time is after petal fall, combining flower thinning and fruit setting to thin out overly dense branches and control competing branches;
The 3rd time is after the hard pit stage, cutting back vigorously growing branches to promote secondary shoots and increase the fruiting area;
The 4th time is in early autumn and late summer, cutting back or thinning out surplus secondary shoots, and pinching the tips of long fruiting branches to moderate vegetative growth and promote flower bud differentiation. Careful summer pruning can greatly reduce the workload of winter pruning, save tree nutrients, maintain balanced tree vigor, increase branching orders, and promote flowering and fruiting. Winter pruning is carried out during the dormant period, that is, on the basis of summer pruning, supplementary pruning is done, mainly to maintain the tree shape and balance vigor, maintain the subordinate relationships among branches at all levels, and regulate the balance between vegetative growth and reproductive growth. It is also called dormant-season pruning.
Pruning Methods for Planting Plum Trees
1. Heading back. That is, cutting off a portion of a 1-year-old branch. According to the degree of severity, it is divided into light heading, medium heading, heavy heading, and extremely heavy heading. Light heading is for relatively strong 1-year-old branches, cutting off about 1/4, so that the branch growth is somewhat moderated, promoting more medium and short branches and cultivating various types of branch groups; medium heading is cutting off 1/3~1/2 of a 1-year-old branch. A plump bud is selected at the cut to promote medium and long branches, mostly used to build the tree framework and to cut and retain main and lateral branches; heavy heading is for weaker 1-year-old branches, cutting off more than 1/2, promoting vigorous branches, making the tree vigor change from weak to strong, mostly used for renewal pruning of main and lateral branches and fruiting branch groups; extremely heavy heading is cutting back at the base of the branch leaving only 2~3 weak buds, promoting medium and short branches, used to cultivate medium and small fruiting branch groups. After a 1-year-old branch of a plum tree is headed back, the vigor of the resulting branches varies depending on the quality of the bud at the cut, the position of the branch, and the direction of extension. A plump, strong, upright branch with a plump bud at the cut is likely to produce vigorous branches after heading back and can be used to cultivate the tree framework; otherwise, it is likely to produce moderate or weak branches and can be used to cultivate fruiting branch groups. Heading-back pruning, under normal circumstances, is not favorable to flower bud formation, but moderate heading back of weak trees or weak branches can reduce the total number of branches and buds in the tree, improve tree nutrition, and favor flower bud differentiation. Moderate heading back or renewal pruning of long and medium fruiting branches can increase the fruit-setting rate.
2. Thinning. That is, removing branches from the base. Properly thinning out overly dense branches or branches in improper positions can improve ventilation and light conditions, save nutrient consumption, and favor flower bud differentiation. However, the number of branches thinned, especially the number of perennial large branches thinned, must not be too many at one time, to prevent causing excessive vegetative growth and affecting the yield of that year.
3. Renewal pruning. That is, cutting back perennial branches that have weakened in vigor, which helps concentrate nutrient supply and promote rejuvenation of weak trees.
4. Leaving unpruned. That is, leaving some 1-year-old branches without any pruning and letting them grow naturally, moderating tree vigor and promoting flower bud differentiation. For upright branches left unpruned, they must first be bent flat or twisted at the base, otherwise the effect is poor. Branches left unpruned must be cleaned up promptly after flowering and fruiting, either by heading back or renewal pruning, to keep the tree shape complete and attractive and favorable for fruiting.
Plum Tree Cutting Propagation
1. Build the seedbed well: In a cool place, set up a plastic shed (bamboo strips, wooden boards, or straw curtain materials are all acceptable), clean up the ground inside the shed, and make a cutting bed with fine river sand. Use 0.5% potassium permanganate solution or 50% carbendazim or 70% thiophanate-methyl or 58% mancozeb 500-fold solution to strictly sterilize and disinfect the cutting bed. The amount of spray should be just enough to moisten the surface of the sand bed. Keep the temperature inside the shed at 20°C to 28°C, and the relative humidity not lower than 70%. Since it is softwood cutting with leaves, natural scattered light must be allowed into the shed to facilitate photosynthesis of the cuttings. The size of the shed depends on the number of seedlings to be raised. Generally, about 250 seedlings can be raised per square meter.
2. Collect cuttings: From disease-free areas, cut current-year leafy softwood shoots from healthy mother trees in full fruiting stage (for early spring cuttings, shoots that did not sprout the previous year can be collected, preferably about 0.7 cm in diameter) as cuttings, 10 cm to 20 cm long, retaining 2 to 3 leaves or 3 to 5 half-leaves at the upper part. The varieties of the cut cuttings must not be mixed, and labels should be attached promptly. The shoots should be semi-lignified and free of pests and diseases. Bundle the collected shoots into bundles of 50 to 100 each, and soak the base portion about 2 cm long in a 0.005% to 0.01% ABT rooting powder No. 1 solution or 0.025% naphthalene acetic acid solution for half an hour to 1 hour.
3. Cut promptly: Use a knife to sharpen the base of the cuttings. Before cutting, first make holes in the cutting bed with a small wooden stick, then insert the cuttings into the holes, with a cutting depth of 5 to 8 cm and a plant spacing of 6 to 8 cm. Water immediately after cutting and promptly cover the shed to retain moisture.
4. Management after cutting: After cutting, pay attention to the temperature inside the shed, the humidity of the bed surface, and ventilation and light transmission. If the temperature is high at noon, spray more cool water. Under the condition of ensuring the temperature and humidity required by the cuttings, the water content of the cutting bed should be reduced as much as possible to prevent rot from excessive moisture. 7 days after cutting, callus tissue begins to form; after 15 days, the cuttings begin to root. When the number of roots reaches more than 10 and the average root length reaches more than 5 cm, they can be transplanted.
Plum Tree Grafting Propagation
1. Rootstock selection: After transplanting and surviving wild peach, plum, cherry, and other tree stumps, cut or saw them off at 6~10 cm above the ground (or according to tree shape) as rootstocks.
2. Scion selection: Choose well-developed 1-year-old, thick, plump-budded, pest-free semi-lignified branches as scion wood, take segments about 7 cm long, and retain 5~7 buds as scions. Wrap the collected scions in a damp cloth and use them as soon as they are collected.
3. Method selection: Generally carried out before the rootstock buds begin to sprout, or when they begin to sprout but have not yet unfolded leaves. The cleft grafting method is commonly used, mainly suitable for thicker rootstocks. This method is easy to master, the graft union heals quickly and firmly, and the survival rate is high.
4. Grafting method: Water the rootstock once the day before grafting. When grafting, flatten the cut surface of the rootstock with a knife, then use a grafting knife or blade to make a straight cleft about 3 cm long. Cut the lower end of the prepared scion into a wedge-shaped cut about 3 cm long, with one side slightly thicker and the other thinner, retaining only 2~3 buds. Then insert the scion into the cleft with the slightly thicker side facing outward and the thin side facing inward, align the cambium, bind tightly and wrap completely with wide plastic strips, and bind the upper cut of the scion tightly with plastic film to prevent water evaporation and pest damage. In dry and windy weather, a transparent plastic bag must be used, with a small cotton ball soaked with enough water placed inside, then cover the part above the graft union and tie the bag opening tightly.
5. Management after grafting: Generally, cutting the rootstock promotes sprouting earlier than bending the rootstock. But in summer, when cutting the rootstock, it must be cut 3-5 cm away from the grafted bud, leaving a few leaves on the rootstock. After the grafted bud sprouts, cut the rootstock again 1 cm above the grafted bud. After cutting the rootstock, remove sprouts promptly, removing all buds sprouting from the rootstock and keeping only the grafted bud. In the later stage, water the seedlings at the proper time. At the end of September, when the grafted bud grows to 70-100 cm, pinch all tips and stop watering to promote thickening growth of the seedlings, make them mature, and improve their overwintering ability.
Now the management of this kind of fruit tree is different from back then. At that time there were only a few scattered trees, so they were not managed very well. Now fruit growers plant them in large contiguous areas. Without good management, it is difficult to get high yields, and thus difficult to make money!