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Epsom salts have gained much attention in recent years as a potential solution to a number of issues in the garden. It’s not quite as straightforward as that, though, so all gardeners should make sure they understand which plants aren’t as keen on Epsom salt.
Many plants do not like Epsom salts, including carnivorous plants, coniferous trees, and tropical plants like tropical palms. Depending on the balance of the soil they are planted in, many other plants may also be damaged by applying Epsom salts.
There can be some benefits to using Epsom salts in the right situations, but if not applied correctly, they can cause some big problems. Read on to find out more about whether Epsom salts are right for your garden.
Why Do Some Plants Not Like Epsom Salts?
As Epsom salts are actually just the crystallized form of a chemical compound called magnesium sulfate, when they are used in the garden, they increase the amount of the two elements that magnesium sulfate contains — magnesium and sulfur — in the soil. Therefore, any potential negative impact is typically caused by one of two reasons:
- The soil now contains too much magnesium
- The soil now contains too much sulfur
Too Much Magnesium
If a plant has access to soil with an abundance of magnesium, the main risk is actually the deficiency of another element. Magnesium and calcium ions in the soil are both positively charged, and the way in which they are absorbed means that they compete with each other to be taken up by the plant.
This means that one of the most common results of having too much magnesium is that a plant may suffer from calcium deficiency, causing a number of symptoms:
- Mis-shapen leaves
- Death of leaf tips
- Chlorosis on leaf edges
- Dark veins
Resolving the problem of too much magnesium can take time, and the usual recommendation is that calcium sulfate can be liberally applied to the bed over a number of years to try to return the ion distribution to a more balanced state.
Too Much Sulfur
The main concern with a plant in soil that has a very high sulfur content is the impact that this has on the pH of the soil. When exposed to water, the sulfur will form diluted sulphuric acid, which will, over time, have a significant impact on the pH level — the measure of acidity or basicity — and this can significantly impact the natural growth of the plant.
The pH level is a critical factor in the ability of natural metabolic chemical reactions to take place. Therefore a high shift towards more acidic soil is very likely to have a significant impact. When soil is too acidic for the growth of the plant, there are a number of common symptoms:
- Stunted growth (for example, when using bong water)
- Dark green leaves tinged with purple
- Brown spots on foliage
- Leaf necrosis
Resolving soil that has become too acidic involves introducing more alkaline substances to the soil in order to neutralize some of the compounds driving the acidity. Agricultural limestone is one such substance that, over time, can bring the pH level of the soil up.
It is also important to remember when trying to resolve an imbalance of chemical compounds within the soil that it should be a slow and steady process. Acting with haste increases the risks of both going too far or having too varied a distribution of compounds across a larger body of soil. Taking steps carefully over time with regular testing is the best way to resolve issues for the longer term.
Why Are Epsom Salts So Popular?
Epsom salts are named after the town in the UK in which it was first discovered — Epsom. While it is similar in appearance to normal table salt, it’s made of a different chemical compound called magnesium sulfate.
Magnesium sulfate is used in lots of industries for many different purposes. To understand what it means for the garden, we need to look at its two constituent parts:
- Magnesium
- Sulfur
When assessing the impact of different chemical elements and compounds on plants, it is useful to refer back to the broadly agreed ‘tiering’ of nutrients for plant growth.
Nutrient Tiers
The plant nutrient tiering system provides a broad reference to the importance of different chemical compounds to plant growth.
Base Nutrients
These are derived from air and water and are critical to all life. They are:
- Carbon
- Hydrogen
- Oxygen
Primary Tier
The three elements occupying the primary tier will be known to most gardeners. They are:
- Nitrogen
- Potassium
- Phosphorus
These elements are considered primary due to the levels to which they are required and because they are heavily involved in the chemical processes that facilitate normal growth, development, and reproduction for the plant.
Secondary Tier
The secondary tier elements play a less direct but nonetheless critical role in the normal functioning of plant life and are still needed in relatively significant quantities. They are:
- Magnesium
- Sulfur
- Calcium
While deficiencies of these elements are less impactful than those in the primary tier, they can still result in substantial negative consequences.
Micro-nutrients
Our final tier covers many remaining elements, such as sodium, zinc, iron, and chlorine, which all play a less prominent role in the plant’s normal functions and are typically found in soil in the trace elements required.
As we can see, both magnesium and sulfur appear as secondary nutrients, playing a very important role in plant health.
Magnesium
Magnesium plays a role in the activation of enzymes that are the chemical catalysts enabling normal plant growth. They are also a direct component of chlorophyll which is responsible for photosynthesis — the process by which plants convert the sun’s rays into energy.
Sulfur
Epsom salts also contain sulfur, which is another nutrient that plants need in reasonable quantities. This element is used in many different chemical reactions, such as the synthesis of amino acids (and, in turn, proteins) as well as oils. It also plays an important role in the creation of chlorophyll and promotes a process called ‘nodulation’ in the type of plants known as legumes.
Benefits
Epsom salts are claimed by many gardeners to have a number of benefits to the garden, such as:
- Preventing a problem known as ‘Blossom End Rot’
- Preventing pests and diseases
- Using as a fertilizer
But unfortunately, there is no real empirical evidence that backs up these claims. There are some limited circumstances where soil might have levels of magnesium that are too low, and in this case, Epsom salts can help. Otherwise, however, it’s likely not to have a significant impact.
Gardening, however, is part science and part art, and anecdotally many gardeners still have a lot of faith in Epsom salts. It’s also been seen for over 100 years as a low-cost way of helping things grow, and with many gardening techniques handed down within families, the tradition that has been created is likely a significant factor in their enduring popularity.
How Do I Know If My Plants Have Magnesium Deficiency?
The perfect plants to benefit from the usage of Epsom salts are those which are deficient in magnesium, as they will immediately benefit from the application of additional magnesium to the soil.
Like most nutritional deficiencies, the first sign of a lack of magnesium in the soil is a visual change to the plant foliage. With magnesium being a key component of chlorophyll — the compound in green plants that is responsible for their color — you can expect to see ‘chlorosis,’ which is another term for the yellowing of leaves.
It’s worth bearing in mind, though, that chlorosis is a symptom of a number of different issues with the plant, and so we need to look further in order to find additional indicators that the problem is related to magnesium. Other issues which can cause chlorosis include:
- Under or overwatering
- Poor aeration, if the soil is too tightly compacted
- Transplant shock
- Diseases, one example being blight
- Other nutrient deficiencies, such as nitrogen deficiency
So we next need to assess where the chlorosis is occurring. The main area we are interested in is the older leaves, which are typically further down the plant. Magnesium should move up the plant for utilization in new growth, and so as the deficiency begins to impact the plant, it should result in chlorosis occurring from the bottom of the plant and moving up.
If you believe that there is indeed a magnesium deficiency, then Epsom salts are the perfect solution. Daily application for a week of a dissolved Epsom salt solution should return the plant back to health.
Do Roses Benefit from Epsom Salts?
One of the most pervasive myths related to Epsom salts is that they can contribute to a more effective bloom for roses. No scientific study has been able to prove this; however, some gardeners swear by it.
Just some of the benefits that have been reported by gardeners are:
- Greener foliage
- Roses growth rate increases
- More flowers appearing
If you do decide to apply Epsom salts, it’s very important to tread carefully; applying anything too aggressively to the soil can have unintended side effects. When considering how to apply it, there are two methods that are most commonly recommended. These are:
- Direct application to the soil
- Preparing an Epsom salts solution and using it to water
Direct Application to the Soil
Epsom salts can be applied directly to the soil around a plant, ensuring that coverage is as evenly distributed as possible so as to have a level effect on the nutritional balance of the soil. One benefit of this approach is that the magnesium and sulfur are more slowly released due to the time taken for exposure to water.
Preparing an Epsom Salts Solution
Another approach is mixing the highly soluble Epsom salts with water in advance. This will typically provide the fastest distribution of nutrients into the soil, and so the amount used should be adjusted in order to account for this.
By mixing with water and then using a watering can evenly distribute the solution over the soil, it will rapidly be absorbed.
Why Don’t Carnivorous Plants Like Epsom Salts?
Carnivorous plants are a firm favorite of many an indoor gardener and are continuing to increase in popularity. Some of the most popular include:
- Pitcher Plant
- Venus Flytrap
- Cobra Lily
- Butterwort
Many enthusiasts will have considered whether you can also utilize Epsom salts across your carnivorous plants, given their popularity in the garden.
A key consideration, though, is the specific requirements of carnivorous plants, as they are often slightly different from most. Carnivorous plants are adapted to grow in poor-quality soil, where the amount of nutrients is limited. They can instead take much of what they need from the insects that they are able to trap and digest.
This means that they are much more sensitive to significant changes in volumes of different compounds in the soil and are more easily overwhelmed. Applying Epsom salts to the soil will increase the volume of both magnesium and sulfur in the soil, so they are generally not recommended across these plants, as with other fertilizers.
Can Epsom Salts Deter Slugs?
Slugs are one of the most common pests in the garden, so any opportunity to deter them from munching their way through your plants is a welcome one.
Provided that you have reviewed the soil to which the Epsom salts will be applied, an application of Epsom salts will deter slugs. They will not be willing to travel over or close to Epsom salts, as touching the compound will draw moisture from them — which quickly kills the pests.
The main issue with using Epsom salts as a means of deterring slugs is that because Epsom salts are so soluble, any application will disappear into the soil as soon as it rains. This means that applying Epsom salts to soil is only, at best, a very temporary solution to deter slugs.
Considering that it is vital to be conservative in the application of Epsom salts to not disrupt the balance of the soil, there are likely to be other more effective solutions to slug removal.
Conclusion
It’s clear that Epsom salts are useful in some circumstances in the garden. Most gardeners, though, will want to tread carefully if they’re thinking about applying it to their flowers or vegetables and ensure they understand how the balance of the soil may change before taking that step.
Sources
- https://en.wikipedia.org/wiki/Plant_nutrition#Macronutrients_(primary)
- https://blog.bluelab.com/magnesium-deficiency-in-plants
- https://myplantin.com/blog/what-plants-dont-like-epsom-salt
- https://www.epsomsaltcouncil.org/gardening/epsom-salt-for-gardening/
- https://www.masterclass.com/articles/epsom-salt-in-garden-benefits-explained
