What are the purposes and effects of shaping and pruning garden flowers?
1. Purposes of shaping and pruning
The ornamental value of flowers is expressed through their form, the amount of flowering and fruiting is cultivated through the canopy structure, and the renewal and rejuvenation of aged plants is compensated through new shoots. All of these need to be adjusted and resolved through shaping and pruning, so the main purposes of shaping and pruning are:
(1) Controlling the size growth of flowers. In the cultivation of ornamental flowers, the plant size often cannot be too large due to environmental or purpose-related limitations. For example, when planted as complementary scenery near buildings, rockeries, lattice windows and poolside areas, the plant height or crown width must be controlled to harmonize with the environment. For flowers planted on rooftops, balconies and similar places, because the soil layer is shallow, the container is small and the space is narrow, the plant size should be controlled even more within a certain range. Ornamental flowers cultivated in indoor gardens of hotels, restaurants and similar places also need to have their stems pressed down and crowns reduced to limit plant size. Apart from considering variety selection, shaping and pruning are usually used for adjustment and resolution.
(2) Promoting flowering and fruiting of flowers. To promote young flowering plants to enter the flowering and fruiting stage as early as possible, and to ensure that flowering plants that have already entered the flowering stage bloom abundantly and bear heavy fruit year after year, shaping and pruning must be carried out rationally and scientifically. In addition, pruning can also achieve the purposes of controlling the flowering period and regulating fruit quantity.
(3) Inducing the renewal and rejuvenation of aged plants. After a plant ages, a large number of peripheral branches die off, and gaps and bare areas appear in the canopy; the scaffold branches become incomplete, causing the canopy to be irregular; the amount of flowers and fruit decreases sharply, and the ornamental charm is lost. At this time, pruning methods can be used to stimulate latent buds in the bark of branches and trunks to sprout, forming thick, young branches that fill the gaps and restore a handsome appearance, achieving the purposes of restoring tree vigor and renewal and rejuvenation.
(4) Improving light penetration conditions and enhancing stress resistance. The vigorous growth of young and mature trees often causes branches and leaves to become excessively dense, resulting in insufficient light inside the canopy and poor ventilation, which easily induces pests and diseases. Through pruning and proper thinning of branches, ventilation and light penetration inside the canopy are increased, branches grow thick and strong, the relative humidity within the canopy is reduced, the stress resistance of the plant is improved, and the probability of pest and disease occurrence is reduced. In areas prone to typhoons, shaping and pruning can change the plant form and reduce branches to decrease wind pressure and prevent branch breakage and trunk toppling.
(5) Controlling the growth direction of branches and beautifying the shape. The cultivation of ornamental flowering plants often requires various artistic forms to express the ornamental design concept, such as waterside style, cascading style, pagoda style and various geometric patterns, animal patterns, etc. Street trees, shade trees, landscape trees and others often conflict with spatial routes, pipelines, buildings and so on when extending toward the surroundings, and these also need to be coordinated and handled through shaping and pruning.
2. Mechanism of action of shaping and pruning
Shaping and pruning can adjust the structure of various parts of the population and individual plants, improve conditions for light energy utilization, regulate the quantity, quality and rhythm of organ formation, coordinate the contradictions between growth and fruiting, and between aging and rejuvenation, and balance the relationships among various parts and organs of the plant.
(1) The dual effects of pruning on plant growth. The main objects of pruning are various types of branches, but their scope of influence is not limited to the pruned branches themselves; it is also manifested in the overall growth of the plant. From the perspective of the whole plant, there are both promoting effects and inhibiting functions.
① Local promoting effect: Because pruning reduces the number of branches and buds, it changes the original distribution relationship of nutrients and water, and nutrients are concentrated to supply the growth of the remaining branches and buds. At the same time, pruning changes the light and ventilation conditions of the canopy, improves the photosynthetic efficiency of leaves, raises the nutritional level of local branches and buds, and thereby strengthens local growth vigor. The strength of the promoting effect is related to tree vigor, pruning intensity and the quality of the bud at the pruning cut. The younger the plant age, the greater the local promoting effect of pruning. Under the same tree vigor, heavy pruning has a more obvious promoting effect than light pruning. When the quality of the bud at the pruning cut is better, the growth-promoting effect of short pruning is more obvious; generally, the first bud below the pruning cut grows most vigorously, while the growth vigor of the second and third buds decreases in turn. Thinning pruning only has the effect of strengthening growth vigor on branches below the pruning cut, while it weakens the growth vigor of branches above the pruning cut.
When pruning, the strength of the bud retained at the pruning cut should be determined according to the specific tree vigor and branch vigor. Generally, leaving a strong bud at the pruning cut can produce thick, long branches; leaving a weaker bud at the pruning cut results in weaker branching; dormant buds can also sprout after stimulation.
The mechanism by which heavy pruning renews and rejuvenates aged plants lies in removing a large number of branches and buds, and even part of the main trunk, so that nutrients are concentrated to supply dormant buds and the remaining branches and buds. With the cooperation of good fertilizer and water conditions, it can also stimulate new roots to form at the root system and improve the physiological activity of the plant, thereby promoting the sprouting and growth of branches and achieving the purpose of renewal and rejuvenation. This renewal and rejuvenation effect is often not very obvious in the first year, and only becomes very prominent in the second and third years.
② Inhibiting effect: After pruning, the canopy is relatively reduced, the number of leaves and leaf area decrease, and the carbohydrates produced by photosynthesis correspondingly decrease; at the same time, the wounds caused by pruning also consume certain nutrients during healing. Therefore, pruning lowers the overall nutritional level of the plant and reduces total growth. The size of the inhibiting effect is related to pruning severity and plant age. If the plant is young, grows vigorously and is pruned lightly, the inhibiting effect is small; conversely, if the plant is old, its growth vigor is declining and pruning is heavy, the inhibiting effect is large, and it often takes a relatively long time to restore growth vigor. Therefore, pruning of plants should be kept moderate. Under normal circumstances, the inhibiting effect of pruning is most obvious in the first year, and as branches and leaves grow, the inhibiting effect is gradually lifted.
Pruning the aboveground part also has dual effects on root growth. When aboveground growth is excessive, pruning can ease competition with the roots for nutrients and water and promote root growth and development. When aboveground pruning is too heavy, the distribution center of nutrients shifts to branches and leaves, strengthening the growth vigor of branches and prolonging the growth period, so that growth cannot end in time in late autumn. Early spring and late autumn are important growth periods for the root system. Heavy pruning lowers the nutritional level of the whole plant, and the nutrients obtained by the roots are correspondingly reduced; therefore, root growth vigor is weakened and the amount of new root formation is greatly reduced.
When pruning, comprehensive consideration should be given, and based on the specific plant condition and cultivation needs, a decision should be made whether to give priority to promotion or inhibition.
(2) The effect of pruning on flowering and fruiting. Pruning can regulate the relationship between vegetative growth and reproductive growth. Vegetative growth is the foundation of flowering; only under the premise of good vegetative growth can the plant flower and fruit normally. However, if vegetative growth is excessive, nutrients are consumed too much and accumulated too little, making flowering difficult; if flowering is excessive and nutrients are consumed too greatly, vegetative growth will in turn be inhibited, causing premature aging of the plant. Reasonable pruning can regulate the balance between vegetative growth and reproductive growth. After pruning, the number of branches and buds decreases, causing nutrients to be relatively concentrated on the remaining branches, making new shoots grow solidly and sprout more side branches.
Branches of different growth intensity should be pruned to different degrees. Weak branches inside the canopy should be heavily pruned because of insufficient light and poor nutritional level within the branch, so as to promote vegetative growth and make it more vigorous. Medium and long branches on the periphery of the canopy with vigorous growth and a higher nutritional level should be lightly pruned to promote the development of many medium and short flowering branches.
At the same time, the sprouting ability and branching ability of branches differ among plants, so pruning methods should also differ. Generally, flowering shrubs with more branch and bud growth points grow more moderately and differentiate flower buds more easily than plants with fewer growth points. Therefore, in production, varieties with strong sprouting ability and branching ability, such as gardenia, serissa, Chinese rose and kerria, are usually heavily pruned to promote more flowering branches and increase the amount of flowering; for some plants with weaker sprouting ability or branching ability, pruning should not be done lightly, because fewer branch and bud growth points are not conducive to lateral bud sprouting and branching, and are also not beneficial to flowering.
(3) The influence of pruning on regulating the nutritional status of flowers. Shaping and pruning correspondingly affect the absorption, manufacture, accumulation, consumption, transport and distribution of nutrients in flowers, as well as the relationships among various nutrients. This is mainly shown in the following aspects: First, regulating the leaf area of the tree body, changing light conditions, affecting photosynthetic production, and thereby changing the level of nutrient manufacture and accumulation in the plant. Second, regulating the balance between the aboveground and underground parts, affecting root growth, and thereby affecting the absorption of inorganic nutrients and the distribution of organic nutrients. Third, regulating the number, proportion and types of vegetative organs and reproductive organs, thereby affecting the nutritional accumulation and metabolic status of the plant. Fourth, controlling ineffective branches and leaves and adjusting the number of flowers and fruit, reducing ineffective consumption of nutrients. Fifth, regulating branch angles, organ numbers, transport pathways, growth centers and so on, and directing the transport and distribution of nutrients.
Tests show that after pruning the aboveground part of deciduous flowers, during the new shoot sprouting period, the nitrogen content in branches and new shoots near the pruning cut can generally be increased, while the carbohydrate content is reduced. The results of pruning tests on evergreen flowers show that pruning can increase the content of nitrogen compounds in the tree body, especially for the two-year-old branches near the pruning cut, strengthening their nitrogen metabolism, improving the nutritional level of shoots, and promoting starch accumulation in leaves, while alcohol-soluble sugars on the two-year-old spring and autumn shoots are mostly lower than those of the control, and decline again at maturity. This indicates that pruning promotes the accumulation, transformation and transport of carbohydrates, and enhances the supply to new tissues (shoots, flowers and fruit).
Because pruning the aboveground part reduces the transpiration area, the water content of the tree body increases and the cell sap concentration decreases. Pruning not only affects the changes in water, carbon and nitrogen in shoots and leaves, and affects the changes in cell sap concentration and transpiration intensity, but also affects chlorophyll content, strongly affects respiration and oxidation processes, and increases catalase activity, thereby promoting photosynthesis, respiration and other metabolic processes and promoting plant growth and development.
In short, pruning regulates the transport and distribution of nutrients in the tree body by changing the number and types of organs, utilizing and changing shoot dominance (apical dominance, vertical dominance), and adjusting branch and bud quality and orientation. However, its regulatory effect also has certain limitations, so it cannot replace basic management measures such as soil, fertilizer and water; it can only cooperate with them to achieve the most perfect cultivation effect possible.
In addition, it must be made clear that no matter which pruning method is used, multiple effects will be produced, some beneficial to plant cultivation and some unfavorable. Therefore, when pruning, these must be carefully weighed and adopted so as to reduce the adverse effects of pruning as much as possible. For example, pruning young plants can form a good plant shape and help them bear fruit earlier, but pruning inevitably removes part of the branches and leaves and causes wounds, inhibiting the growth of the whole plant. Therefore, on the premise of achieving reasonable shaping, light pruning is better for young plants.