Understanding Magnesium Deficiency in NZ Soils
Magnesium deficiency is a common problem in New Zealand gardens, particularly in acidic soils and areas with high rainfall. When your plants—especially fruit trees—show signs of yellowing leaves while the veins remain green, magnesium deficiency is often the culprit. This nutrient plays a vital role in photosynthesis, helping plants convert sunlight into energy.
NZ soils, particularly in regions with leaching from heavy rain, can lose magnesium over time. Clay-based and sandy soils are especially prone to this issue. Recognising the symptoms early means you can intervene quickly and restore your plants to health.
Symptoms of Magnesium Deficiency in Fruit Trees
Yellow leaves between the veins (interveinal chlorosis) is the classic sign. On lemon trees and other citrus, this yellowing typically appears first on older leaves near the base of the tree, then progresses upward. The leaf margins may also take on a reddish or bronze tint.
Other symptoms include reduced fruit size, poor flowering, and overall stunted growth. If left untreated, the tree may drop leaves and become stressed, making it vulnerable to pests and disease.
Why Epsom Salts Work for Magnesium Deficiency
Epsom salts—magnesium sulphate—are a fast-acting, affordable solution for correcting magnesium deficiency. Unlike soil amendments that take months to break down, Epsom salts dissolve quickly and are readily absorbed by plant roots and foliage. This makes them ideal for treating yellowing fruit trees.
Tui Epsom Salts are specially formulated for NZ gardens and dissolve easily in water, making application straightforward whether you're treating a single lemon tree or multiple fruit trees across your property.
How to Apply Tui Epsom Salts to Fruit Trees
Soil Application: Dissolve 1 tablespoon of Epsom salts per litre of water. Water the solution directly around the base of each tree, ensuring it reaches the root zone. For mature trees, use up to 2 litres per application. Apply once per month during the growing season (September to April).
Foliar Spray: Mix 1 tablespoon of Epsom salts per litre of water and spray directly onto the foliage, covering both sides of the leaves. Early morning or late afternoon application works best to avoid leaf burn. Repeat every two weeks for visible improvement.
Granular Application: Scatter granules around the base of the tree and water in thoroughly. Follow package instructions for application rates based on tree size.
Fruit Tree Fertiliser Requirements in NZ
Magnesium is just one piece of the puzzle. Healthy fruit trees need a balanced approach to fertilising. Most NZ fruit trees require nitrogen for leaf growth, phosphorus for root development and flowering, and potassium for fruit quality and disease resistance.
Apply a balanced citrus or fruit tree fertiliser in spring (September) and again in early summer (December). Combine this with Epsom salt applications to address magnesium needs specifically. Avoid over-fertilising, which can cause excessive leaf growth at the expense of fruit production.
Fixing Yellow Leaves on Lemon Trees
Once you've identified magnesium deficiency as the cause, act quickly. Start with a foliar spray of diluted Epsom salts for rapid absorption—you should see improvement within two to three weeks. Follow up with soil applications to address the root cause and prevent recurrence.
Check your soil drainage and pH. Lemon trees prefer slightly acidic soil (pH 6.0–7.0). If your soil is too alkaline, magnesium becomes locked up and unavailable to roots, even if present. Adding organic matter like compost improves soil structure and nutrient availability.
Prune out severely damaged leaves to encourage new, healthy growth. Water consistently—stressed trees are more prone to nutrient problems. Mulch around the base with 5–7cm of wood chips to retain moisture and regulate soil temperature.
Prevention and Long-Term Care
Regular applications of Epsom salts during the growing season can prevent deficiency from developing. Many experienced NZ gardeners treat fruit trees with Epsom salts monthly as preventative care, particularly on older trees or in areas with naturally magnesium-poor soils.
Combine Epsom salt applications with a well-rounded fertiliser programme, good drainage, and consistent watering. Healthy, well-nourished fruit trees are more resilient and productive, rewarding your care with vibrant foliage and abundant harvests.