Reasons for the Yellowing of Rose Leaves
Roses are被誉为 the queens of flowers, but the problem of yellowing leaves plagues countless rose enthusiasts. As a perennial woody flowering plant, yellowing leaves not only affect the ornamental value but also indicate potential health issues in the plant. This article will systematically analyze the five most common causes and provide professional solutions to help you restore lush green leaves.
I. Improper Light Management
1.1 Mechanism of Sunburn Injury
Although roses enjoy sunlight, the intense UV radiation exceeding 35°C at noon in summer can damage the chloroplast structure. Symptoms such as the edges of new leaves becoming scorched and the overall yellowing of old leaves are typical, especially for potted roses whose roots are more easily damaged due to limited space.
1.2 Scientific Shading Solution
Use a sunblock net with a 50% shading rate and set up temporary shading from 10:00 to 15:00. For ground-planted plants, a green hedge can be planted on the west side to form a natural barrier. Move the plant to a scattered light environment immediately after yellowing leaves are detected.
II. Imbalance in Water Regulation
2.1 Symptoms of Yellowing Due to Water Deficiency
When the soil moisture content is below 30%, the plant initiates a self-protection mechanism, giving priority to the water supply for new buds (G-Y). This is manifested by the gradual yellowing of lower old leaves from the tip to the petiole, and severe cases may be accompanied by leaf drop.
2.2 Precision Irrigation Techniques
Follow the principle of "watering when dry and moist": water thoroughly when the topsoil 2cm is dry. Measure the moisture content twice a day in summer, early morning and evening, and use the immersion method to ensure even penetration of water. It is recommended to install an automatic drip irrigation system to maintain the substrate humidity at 60%-70%.
III. Malnutrition
3.1 Principle of Fertilizer Burn
Excessive nitrogen fertilizer causes exudation of cell sap and the roots to turn brown and rot. When the EC value is >2.5mS/cm, old leaves show symptoms of burnt edges and yellowing, and new leaves become wrinkled and deformed. Unripe organic fertilizer can produce hydrogen sulfide poison.
3.2 Scientific Fertilization Strategy
Fertilize in spring and autumn with an N-P-K ratio of 18-18-21, once a month. If fertilizer burn is detected, immediately remove the plant from the pot, wash the roots, and disinfect with a 1000x solution of carbendazim before replacing the soil. It is recommended to use slow-release fertilizer and combine it with seaweed extract to adjust the soil environment.
IV. Environmental Stress Factors
Day-night temperature differences >10°C can easily cause physiological yellowing of leaves, with the best range being 15-18°C at night. When the air humidity is below 40%, use misting to increase humidity, but avoid water accumulation on the leaves that can lead to fungal growth.
V. Pest and Disease Invasion
Spider mites absorb the sap from the back of the leaves, causing star-shaped yellow spots. Rotate the use of bifenthrin and pyridaben every 7 days. Root rot can be treated with pyraclostrobin, while also improving drainage conditions.
By systematically investigating environmental factors and precisely adjusting maintenance measures, more than 95% of rose leaf yellowing issues can be improved within 2-3 weeks. It is recommended to establish a maintenance log, recording data such as temperature, humidity, fertilization, and watering to achieve scientific management. Regularly supplement with chelated iron fertilizer and use EM bacteria to improve the soil, which can effectively prevent yellowing due to nutrient deficiencies.