Which Plants Do Not Like Manure?

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Using manure is a firm favorite of many gardeners due to the significant positive impact it can have on the growth of many plants. It’s an easy assumption to make that all plants will benefit, but that’s not always the case. With that in mind, which plants do not like manure?

Root vegetables and flowering plants like peppers and tomatoes do not like manure. The extra nitrogen will increase the growth of foliage at the cost of the roots, fruits, and flowers. If some manures are not prepared properly, it can also result in fertilizer burn.

Understanding whether using manure is appropriate in your garden is not always easy. Read on to explore the use of manure in more detail and whether it’s right for you.

Why Do Some Plants Not Like Manure?

There are two main reasons that we might say that some plants do not ‘like’ manure. First, we need to bear in mind that most manures typically provide a high level of nutrients to the soil. These nutrients are varied, but there are often three in particular that are discussed across chemical fertilizers:

Nitrogen

Potassium
Phosphorus

In the case of manure, the key nutrient that has the greatest concentration and impact is the level of nitrogen. The level of nitrogen in manure is often referred to using a scale of hot and cold, with hot manure having a high relative concentration of nitrogen and cold manure having a lower level.

Nitrogen is a vital factor in plant growth, as it is a key component of chlorophyll, which is what the plant uses to convert sunlight to energy via photosynthesis. The process of photosynthesis is what then allows the plant to grow. We can see, then, that nitrogen is important because it is how the plant ensures there is enough energy available to grow.

Once manure is applied to the soil, it breaks down, and its nutrients pass into the wider area. This causes an increase in the amount of certain elements in the soil by relative density. The significant increase in nitrogen that manure can provide can sometimes be a bad thing, and there are three reasons for this.

Manure changes the way the plant grows

Bacteria content
Fertilizer burn

Manure Changes the Way The Plant Grows

The main reason that for some plants, we consider them to not like manure is not because the manure changes the way the plant grows. Having high nitrogen availability in the soil means that the plant does not need to take action to reach the nutrients in the soil that it requires, and this typically results in two things:

High foliage growth (leaves)
Low root, flower, and fruit growth

For many plants, especially vegetables, this is exactly the opposite of our usual objective. We want plants like carrots and tomatoes to have a high yield, and significantly increasing the amount of nitrogen available in the soil by using manure can act against us.

Bacteria Content

When looking to apply manure to vegetables, especially mid-season vegetables, a key consideration should be how fresh the manure is. This is because manure can often contain harmful bacteria which we do not want to consume. This is especially true of E. coli, as the symptoms are very unpleasant, including:

Diarrhea
Vomiting

Stomach cramps

It can also lead to serious complications in those with weakened immune systems, and so it’s certainly something we want to take all reasonable steps to avoid. The vast majority of strains of E. coli will be killed in compost kept at 131F for several days, although at least one strain requires a sustained period of 160F to be removed.

A good rule of thumb here is that if you are growing vegetables like carrots, where the edible part is in contact with the soil, then composted manure should only be applied at least four months prior to harvesting – this gives enough time for any bacteria in the soil to dissipate and lessens the chance of contamination.

Fertilizer Burn

The second reason is fertilizer burn. This is far more common with non-organic fertilizers, but in certain types of manure that have not been composted and are fresh, it can be a concern. This is because, with high levels of nitrogen, salt, and especially ammonia, plants can be overwhelmed and take damage from what are effectively chemical burns.

The best way to avoid damage from fertilizer burns is to ensure that the manure has been adequately composted. The general recommendation for this is that it has to be kept at a temperature of at least 131F and for at least 15 days. Doing this provides time in an environment that will encourage enough of the organic compounds to break down into constituent parts, and so will have less chance of damaging the plant.

What Are the Different Types of Manure?

When we talk about manure, it means both the solid and liquid waste of an animal. What is often forgotten, though, is that it also includes the material used to gather and contain the waste matter — typically a carbon-rick material such as hay or wood shavings.

Here is more on using manure in your garden.

It is important to compost manure ahead of using it both for health and effective plant growing reasons. The way in which you use the composted manure will also depend on what it contains, and the main factor of this is what animal it came from. There are a number of common animals whose waste is used for manure:

Cows

Horses
Sheep
Chickens and other poultry

Other types

Cows

Cow manure typically has the lowest nitrogen content and so is sometimes called the ‘coldest.’ This is because cow manure typically contains a relatively high level of liquid versus other manure types. One of the benefits of cow manure is a high level of different bacteria which are beneficial to soil quality.

Horses

Horse manure is a popular choice for use in the garden and is probably the most common type of manure in use. This is partly because it has a high nitrogen content and so is considered to be relatively ‘hot.’ It is very low in its levels of potassium and phosphorus, which are important for rooting and fruiting, so horse manure should not be used on flowering and fruiting plants as it will reduce the expected yields.

Sheep

Sheep manure is even hotter than horse manure in terms of its nitrogen levels. A big difference between sheep and horse manure, though, is that sheep manure also contains high levels of phosphorus, which is said to give it a better balance. It’s still relatively rich, however, so it should again be used with caution.

Chickens and Other Poultry

Poultry manure has a very, very high nitrogen content and so is considered to be very ‘hot.’ You only need to work a small amount of this manure into compost in order to leverage its nitrogen once it has been allowed to break down over time.

Poultry manure is, however, one of the main sources of fertilizer burn for organic fertilizer, so caution should be taken when looking to apply it across plants.

Other types

You may sometimes see other types of animal manure available, although that’s typically much rarer as a result of either poor ‘yield’ or a manure content that is not particularly in demand. The main type of manure that should never be used is that from meat-eating animals, as this can contain dangerous parasites that do not appear in manure from herbivores.

What Are Organic Fertilizer Alternatives to Manure?

If you appreciate that adding manure to tubers like carrots or fruiting plants like peppers might impede the yield, you might wonder what your alternatives are. In these instances, it is important to consider how the plants grow and what encourages the type of growth that you want to see.

It’s also worth keeping our focus on organic fertilizers, as they have a number of benefits — especially:

Generally, easier to use
Better for the environment

Generally, Easier to Use

The main reason that organic fertilizers are often considered easier to use is that they are not as strong as chemical fertilizers. Not being as strong may sound counterproductive, but beginners have a tendency to overfertilize, and doing so with strong chemical fertilizers can damage the plants, having the opposite effect.

Some plants, when heavily over-fertilized, can also enter a state called ‘lockout’ where the harsh conditions that the chemical fertilizer creates cause the plant to stop almost all absorption to limit the damage to itself. This means that the plant will struggle to grow, and you may have created a hostile environment in the soil that can persist for some time.

Using organic fertilizer means that there is more leeway for the gardener. A more gentle approach can often be the best one, and organic fertilizer tends to provide this, given its more natural composition.

Better For the Environment

Organic fertilizer is much better for the environment. Chemical fertilizers have a much higher risk of exposing the environment to unnatural levels of elements like nitrogen, which can have far-reaching effects. The two main problems are:

Eutrophication
Greenhouse gas production

Eutrophication

This is where excess nitrogen in the soil makes its way into waterways, which can change the dynamics of the ecosystem there. You can expect to see a boom in the amount of algae, as it uses nitrogen to grow, but this disrupts the ecosystem and can cause problems for the fish and other life living close by.

Greenhouse Gas Production

The high level of nitrogen in the soil can encourage the growth of bacteria which produce greenhouse gases such as carbon dioxide. At scale, this can result in a significant amount of unwanted gases making their way into the atmosphere.

Organic Alternatives to Manure

With all that in mind, there are a number of organic favorites that are an alternative to manure. They typically focus on higher levels of the other key components of fertilizer other than nitrogen — namely Phosphorus and Potassium.

Standard compost

Wood ash
Coffee grounds
Kelp meal

Bone meal

Standard Compost

Regular compost is arguably the most important element of any fertilizer for plants that aren’t keen on manure. This is because it provides vital benefits to the soil structure and quality whilst also providing a gentle supply of nutrients as microorganisms break down the organic matter.

Wood Ash

Wood ash is a great source of both phosphorus and potassium, and so during the initial growth stages of fruit-bearing plants, it can help the plant ensure it has the nutrients it needs. Bear in mind, however, that it should be used sparingly in order to reduce the acidity impact it has on the soil.

Coffee Grounds

Coffee grounds provide a gentle release of a low nitrogen level, and so can be a more forgiving way to provide a base level of nitrogen to your plants.

Kelp Meal

Kelp meal is a great way to add potassium to the soil. This is especially important for the later flowering and fruiting stages of plants like tomatoes.

Bone Meal

Bone meal is another great way to add phosphorus to soil and is crucial during the initial growth stages.

As you can see, the key to assessing organic fertilizer for your plants is understanding the balance of elements and weighing them alongside the needs of the plants at different stages of their seasonal cycles.

This means that, given that there are endless different possible sources of organic fertilizer for your plants, if you are armed with an appropriate understanding of the needs of your plants and the composition of your fertilizer, you should be in a position to make good choices on behalf of your plants. And if in doubt, it’s good for beginners to bear in mind that too little is generally always better than too much.

Conclusion

Manure is a powerful tool for a gardener looking to get the most out of their plants. With the different types of manure available and the variety of plants you might be thinking about using manure with, it’s well worth considering whether using manure will help meet your objectives.

Sources

https://kids.frontiersin.org/articles/10.3389/frym.2020.00063

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