Every hobby gardener knows that plants need magnesium. But why is that and how can garden plants be adequately cared for? We explain the background, provide basic knowledge about needs-based fertilization, present plants with a particularly high magnesium requirement and give tips on the safe use of the fertiliser.


Magnesium (chemical symbol Mg) is one of the most important plant nutrients, along with nitrogen, potassium and phosphorus. It is contained in the soil. Sandy soils are poorer in magnesium than the heavier soils.

Photosynthesis is not possible without an adequate supply of magnesium. The plant is then unable to form chlorophyll, the green plant pigment. This contains magnesium.

Especially in the growth phase, garden plants have a high magnesium requirement. In agriculture, undersupply means high yield losses.


You can tell if your plants are suffering from a magnesium deficiency by the following symptoms:

  • rust-brown spots on the leaves
  • cloud-like, yellowish discolouration (chlorosis) between the dark green leaf veins
  • inhibited water uptake
  • reduced growth
  • Deficiency symptoms appear first on older leaves
  • continuous increase in symptoms

Reasons for the magnesium deficiency:

  1. Magnesium is a mobile element. Heavy rainfall or irrigation during dry periods wash the magnesium out of the soil and can cause a deficiency.
  2. Potassium, manganese and calcium are the antagonists of magnesium. A high content of these elements in the soil prevents the plants from absorbing magnesium. Even calcareous irrigation water can lead to magnesium deficiency symptoms.
  3. Damage to the roots can be the cause of reduced magnesium absorption.
  4. Light, sandy and acidic soils naturally contain less magnesium than heavy and medium-heavy soils.

There are various magnesium fertilizers available on the market that will quickly remedy the situation.

Types and properties of magnesium fertilizers

1. Epsom salt

  • available separately or as part of complete fertilizers
  • very water soluble
  • quickly effective in case of visible deficiency symptoms

2. Voting

  • contains magnesium and sulfur
  • lower water solubility
  • good for soil fertilization

3. Kalimagnesia/Patentkali

  • solid fertilizer
  • contains potassium, magnesium and sulfur
  • ideal for bed preparation or nitrogen-free autumn fertilization
  • also suitable for salt-sensitive plants
  • incorporate well after the order

4. Magnesiumkalk

  • ground dolomite rock
  • contains calcium and magnesium
  • regulates the pH of the soil

Tips for short-term use in plants with deficiency symptoms:

  • Prepare magnesium fertilizer according to package directions
  • Spray plants with water first
  • fertilization after rainfall is recommended
  • apply liquid magnesium fertilizer (spray solutions) with a garden sprayer
  • also note the underside of the leaves
  • Scatter and incorporate solid fertilizer
  • repeat at 14-day intervals

Tips for long-term prevention:

  • Carry out liming of the soil (target: pH value 5.5)
  • once a year application of 70 to 100 grams of magnesium fertilizer per square meter
  • alternatively use complete fertilizer containing magnesium

soil analysis

Regular magnesium fertilization does not make sense. A one-time fertilization a year to prepare a good soil is helpful and sufficient. Otherwise, the additional supply is only necessary if your plants show signs of deficiency or a soil analysis shows a lack of plant nutrients. Professional soil analyzes are offered in specialist garden shops and nurseries.

Tip: Basically, heavy soils are considered to be well suited for storing nutrients. The regular application of compost to the beds already leads to a good supply of magnesium to the garden soil.

Guide values ​​for the optimal magnesium content in the garden soil

  • light soils: 7 milligrams per square meter
  • medium-heavy floors: 10 milligrams per square meter
  • heavy soils: 15 milligrams per square meter

Plants with a high magnesium requirement

All plants need magnesium to form chlorophyll and for photosynthesis. But the needs are different. In addition to the requirements of the plants, always pay attention to the nature of the soil.

Most hobby gardeners are aware of the high magnesium requirement for box trees and conifers. Special fertilizers for these plants that are available in specialist shops contain magnesium. Yews, firs, pines, spruces and all conifers are also considered plants with a high need. The reason for this is that, unlike deciduous trees, conifers do not utilize the nutrients from the needles before they lose them. They therefore require an adequate supply of magnesium for regeneration. Coniferous trees also grow on light, sandy soils that contain less magnesium anyway. Deficiency symptoms in coniferous trees become visible through white or yellowish discoloration of the needle tips. Only later do the needles completely discolor and fall off.

However, plants that grow in acidic soil, such as rhododendrons or hydrangeas, require a good supply of magnesium. Otherwise, yellowish leaf discoloration quickly appears with green leaf veins. The discoloration first appears on the older leaves. This is considered to be a clear distinction from iron deficiency, which first becomes apparent through yellowish color changes and dying off at the tips of the shoots.

Currants, strawberries, raspberries and gooseberries are sensitive to a magnesium deficiency. The consequences are clearly visible leaf chlorosis, leaf fall and reduced fruit formation.

All types of cabbage, which are known to be important suppliers of magnesium in human nutrition, need heavy, magnesium-rich soil for good development.

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