Epsom salt is the colloquial term for magnesium sulfate (MgSO4), a crystalline salt compound that dissolves in water. This mineral salt is commonly obtained from geological formations and dried lake beds. It can be used as a culinary salt substitute, as a supplementary source of minerals in marine aquaria, or as a magnesium and sulfate-rich resource for intensely farmed crops.
As Epsom salt is pH neutral, its application into prepared substrates does not significantly alter their alkalinity levels. The chief purpose of its application in farms is simply to counter magnesium deficiency levels. Some gardeners believe that it aids in the control of pests, improves seed germination and flowering rates, and enhances the ability of roots to take up nutrients. Take note that these claims have yet to be scientifically supported.
Magnesium is a vital element as it forms the core of all chlorophyll molecules in plant cells. Its deficiency, though uncommon in well-draining soils, can lead to major problems like leaf discoloration and stunted growth, both of which affect photosynthesis rates. The application of Epsom salt is especially beneficial for evergreen and flowering perennials. Using it only when a magnesium deficiency has been detected is key to improving plant development without compromising nutrient absorption rates.
- PURE EPSOM SALT: Made with pharmacy-grade magnesium sulfate to help ease aches and soreness from muscle pains
- FRAGRANCE FREE: Fragrance-free and fast dissolving, ultra-fine crystals dissolve quickly in water
- HOW TO USE: At bedtime, pour 2 cups under warm, running bath water and soak for 20 minutes
1) Azaleas & rhododendrons (Rhododendron spp.)
Widely cultivated as ornamental plants due to their vividly colored inflorescences, azaleas and rhododendrons are deciduous and evergreen shrubs. Some exceptional members of the Rhododendron genus can even be maintained as small trees. Though they tend to have low nutrient requirements compared to other flowering shrubs, their best features are brought about by an occasional boost in organic materials.
In poor soils or in neutral to slightly basic substrates, azaleas and rhododendrons may fail to flower at desirable rates. Adding Epsom salt around the base of these shrubs should help promote bud production. If the soil is especially low in trace nutrients, Epsom salt can be added as much as 1 – 2 times per month. A tablespoon of salt for every area of 10×10 feet (3×3 meters) should suffice. This can simply be worked into the upper layers of soil around the root zone.
Azaleas and rhododendrons require optimal amounts of sunlight to fully benefit from the application of Epsom salt. In full shade, most popular cultivars will fail to produce a satisfactory number of blooms despite the generous application of fertilizers. To avoid adversely affecting your shrubs, aim to conduct a soil test for magnesium and sulfur levels beforehand.
2) Pepper plants (Capsicum spp.)
Now cultivated far outside of their native ranges to meet global demand, peppers are known for the burning sensation of their oils. These contain capsaicin, a chemical that most animals find unappealing. Some peppers have been bred to be remarkably hot, whereas others are mild enough to be flavorful without packing a punch.
Magnesium, as a secondary or trace nutrient, is commonly deficient in farmed red bell peppers. For this reason, they can benefit from the addition of Epsom salt. Signs of magnesium deficiency include marginal chlorosis, which initially affects the older leaves. Over time, even young leaves may lose most of their green pigmentation. Due to the loss of chlorophyll molecules, bloom and fruit production may be significantly reduced or arrested.
Epsom salt can help give pepper plants a healthy magnesium boost. It can also improve the germination rates of their seeds and the development rates of both starter and mature plants. Simply mix a conservative amount of the salt into the germination mixture or around the base of older plants. In due time, and when provided with favorable conditions, they should begin to produce the most vibrant fruits.
3) Tomatoes (Solanum lycopersicum)
Grown for their acidic, sometimes sweet, and incredibly tasty fruits, tomatoes are some of the most valuable crops for a vegetable garden. Today, they come in hundreds of subtly different varieties, each with its unique set of cultivation requirements. As vines, they tend to require vertical support to grow to their maximum heights. When portions of their shoots come into contact with the substrate, they may produce new roots.
Tomatoes typically require supplementary nutrients to produce desirable amounts of their flowers and fruits. Even outside the fruiting period, they can benefit from a well-balanced supply of trace nutrients. However, these should only be applied to substrates with deficiencies. In tomatoes, magnesium deficiency is manifested by interveinal chlorosis or mottled discoloration. Over time, the deficient leaves may die back.
Epsom salt should ideally be used for tomatoes even prior to the onset of deficiency symptoms. If the substrate has been determined to be low in magnesium, you may water young tomato plants with an Epsom salt solution. This can be done as often as once a month. Always use conservative doses of Epsom salt as an overdose can lead to calcium deficiency (usually leading to blossom end rot).
4) Roses (Rosa spp.)
The most popular ornamental plants due to their association with love and romance, roses flourish when their roots are provided with primary nutrients (nitrogen, phosphorus, and potassium) and trace elements. The regular provision of fertilizers boosts their root growth and flower production rates. Magnesium deficiency is quite common in stands of roses that are rooted in poorly-nourished gardens and landscapes.
The most common symptom of magnesium-poor conditions is the deterioration of older leaves. These start to die back by turning yellow along their margins. Over time, the affected leaves may become necrotic. The use of Epsom salt is the conventional means of preventing these symptoms, though it should be applied to rose bushes just 2 – 3 times annually. The salt can be applied in its solid form or as a water-based solution around the base of the bushes. Do not use more than ¼ cup of salt per mature plant.
Note that the overfertilization of rose bushes is a common problem. If you suspect that you may have worked too much salt around the base of your plants, you can heavily water them to increase dilution rates. Excess salt can lead to root burn, intensely dark leaves, and calcium deficiency. For this reason, you should test the soil prior to applying nutritional supplements.
5) Cucumber (Cucumis sativus)
The humble cucumber, set apart by its high water content (95% of the fruit is water), is one of the oldest annuals to be cultivated as a food source. This vine spreads by creeping over rich substrates and by using its shoot’s tendrils to latch onto supporting structures. Its cylindrical fruits, which have high concentrations of vitamin K, are actually a type of berry. The quality of its multi-lobed and pointy leaves reveals much about the health of its roots and the nutrients they can access.
If your cucumber vine’s leaves are turning yellow, they may indicate deficiencies in magnesium and iron. If you notice that the discoloration begins in the regions between major veins, it may be time to incorporate Epsom salt into the upper layers of soil. Less than a single teaspoon of this salt (per mature plant) should be enough to balance out the substrate’s nutrient profile.
Epsom salt can maintain your cucumber plants’ spritely appearance and overall vigor. However, to avoid shocking the roots, it should only be applied once during the growth season. To directly aid in leaf recovery, you may make use of an Epsom salt-based foliar spray. Mix a tablespoon of the salt in a gallon of fresh water, allow them to dissolve, and transfer the solution into a spray bottle for easy usage.
6) Lettuce (Lactuca sativa)
A versatile, highly nutritious, and hardy plant, lettuce is now one of the most commonly cultivated types of leafy greens. It is grown in all sorts of traditional and modern setups, including farms that make use of cutting-edge hydroponic technology. Botanists have the nutrient requirements of the most economically valuable varieties down to a science. Deficiencies or excess concentrations of specific nutrients can quickly alter the appearance of lettuce leaves.
Low levels of magnesium affect older lettuce leaves by altering the color of their margins and interveinal zones. If left untreated, these leaves may quickly become necrotic and unsightly. As lettuce leaves need to be evenly colored and crisp to retain their market value, magnesium deficiencies can lead to financial losses in farms. The application of an Epsom salt solution should help affected plants recover.
A teaspoon of Epsom salt dissolved in a gallon of water should suffice as an organic fertilizer for magnesium-deficient lettuce. Unless you’ve detected magnesium-deficient conditions, do not incorporate Epsom salt into substrates around lettuce roots. Excess amounts of magnesium may affect how efficiently they take up other trace nutrients.
7) Hydrangeas (Hydrangea spp.)
Hydrangeas tend to be heavy feeders, especially during their bloom period. They usually benefit from conservative doses of well-balanced fertilizers and organic nutrient sources, like eggshells, Epsom salt, and compost. Deciduous or evergreen, they can quickly develop into medium-sized shrubs bearing heavy bouquets of attractive blooms. Both the quality and longevity of the inflorescences are affected by the health of these species’ leaves.
Known for having blooms that change in color depending on the alkalinity properties of the soil, hydrangeas are hyperaccumulating plants. They can grow in a wide range of pH conditions, which affects how well the roots can take up aluminum and other trace elements. When magnesium levels are low, the leaves may increasingly turn yellow and may become necrotic. An increase in unhealthy and dropped leaves leads to reduced bloom rates.
Once you’ve determined that the soil around your hydrangea’s roots has low levels of magnesium, you can water the area with an Epsom salt solution. A single tablespoon of salt can also be worked through a surface area of about 10×10 feet. Make sure to distribute the salts evenly as pockets with higher concentrations of magnesium can adversely affect the roots.
Plants That Don’t Like Epsom Salt
There continues to be much contention about the use of Epsom salts, especially as not all plants respond to supplemented magnesium and sulfur in the same way. Some sensitive species can quickly become damaged due to exposure to salts, even in acidic and magnesium-poor substrates. For some plants, a well-balanced fertilizer or a store-bought, mineral-rich potting mix should suffice to provide them with all the magnesium and sulfur they need.
It must be noted that, in many cases, the unnecessary usage of Epsom salts (in soils that do not have an existing magnesium deficiency) leads to unfavorable symptoms. Some horticulturists avoid using salts as they prefer fertilizers or organic mixtures, like compost, that are not composed of just a single nutrient or mineral. Consider using manure, a slow-release fertilizer, or enriched compost for the magnesium-sensitive plants below:
- Common tropical houseplants like monsteras, fiddle leaf figs, palms, and philodendrons
- Carnivorous plants
- Conifer trees
- Ornamental plants in soils that have normal levels of magnesium
Magnesium toxicity occurs when substrates that are already high in nutrients, including magnesium, are supplemented with compounds like Epsom salt. This can be dangerous to plants because their capacity to absorb other nutrients becomes affected. In cases where symptoms like chlorosis are observed, even if magnesium levels are adequate, do not use Epsom salt. Instead, you can manage the availability of nutrients by controlling pH levels.
