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Gardeners love spending time outdoors, so they gravitate towards recycling more than most. When the opportunity of using tea and tea leaves in the garden comes up, it sounds like the perfect opportunity to help the garden and recycle some kitchen waste. With that in mind, it’s more important to consider which plants won’t benefit from the leftovers from your cup of chai.
Many plants dislike tea, including chrysanthemums, daisies, and marigolds. This is because tea contains tannic acid, which contributes to the soil’s acidity. Applying tea to some plants can have significant negative effects, so caution is advised.
How do we know whether plants will benefit or not from using tea as a fertilizer? Read on to find out more about whether your garden will benefit from tea or if you’re better off avoiding it altogether.
Why Do Some Plants Not Like Tea?
Tea is one of the world’s most popular drinks, with estimates putting it in the top three most consumed drinks on earth, alongside water and coffee. Tea’s history spans thousands of years, likely beginning in China and northern Myanmar and making its way slowly but surely across the entire world.
The impact of tea on plants comes largely as a direct result of the composition of tea leaves. These leaves contain a number of different elements and compounds that can have an effect on plants.
Tannins are a type of compound called a plant polyphenol. They are commonly found in different forms across most plants on earth and possess certain properties. The most important tannin when considering the impact of tea on plant growth is tannic acid.
Tannic acid possesses a number of different phenol groups in its chemical structure, and this provides it with a weak acidity. This means that when applied to the soil, it can cause the acidity (or basicity) levels of the soil to fall lower, indicating that the soil has become more acidic.
All plants generally prefer a specific level of acidity in the soil, usually dependent upon how they have evolved and in what areas — plants that have evolved in areas with highly acidic soil learn to prefer it, and vice versa.
Therefore if plants undergo a shift in soil acidity, it may reduce their ability to take on nutrients effectively. This is one way in which plants may be considered not to like tea or tea leaves as a fertilizer.
Nitrogen, Phosphorus, Potassium, and Manganese
Tea leaves contain high levels of nitrogen, and less so the other elements here. An assessment of dry tea leaves has shown the following levels of different elements:
- Nitrogen – 4.4%
- Phosphorus – 0.25%
- Potassium – 0.25%
- Manganese – trace
4.4% is a relatively high level of nitrogen versus many fertilizers targeting the high end of what can be considered normal growth. However, nitrogen in tea leaves is not easily given up, so it’s likely that nitrogen won’t play a role in some plants reacting poorly to tea leaves.
The levels of phosphorus, potassium, and manganese are also not likely to be of significant concern.
However, if a plant is already in an environment where the soil contains too much of any of these elements, increasing them further through fertilizing the plant with tea leaves will not have a beneficial effect. It may result in inhibited growth if it causes the plant to cross over a threshold of nutrient volumes that is too much for normal growth.
Aluminum is widely known to be toxic for plants. It is considered to be one of the most substantial issues when looking at the causes of plant growth inhibition in acidic soils, in which aluminum is more likely to be present. There are a few things that aluminum impacts:
- Cell walls
The way that aluminum inhibits growth is predominantly by encouraging excess root growth. Aluminum, as an element, is highly reactive, and unfortunately, this means that it can have significant negative effects across many areas of the plant, including plasma membranes and cell walls.
Although the levels of aluminum in tea leaves are relatively low, the exact levels will vary according to a number of different factors, such as the variety of tea, how it was grown and with what fertilizer was used. This is one important factor in considering the negative impact that tea can have on plant growth.
The varieties of tea that are most commonly grown today are known as fluoride hyperaccumulators. This means that they are especially good at absorbing fluoride and some other compounds. As a result, tea leaves have a relatively high concentration of fluoride, and when used as a fertilizer, this can make its way into the soil.
Fluoride is not readily taken up in most plants (tea being an exception); however, fluoride is a poison for plants, working its way through root systems and gathering in leaf edges. Fluoride strongly inhibits the ability of the plant to photosynthesize and also prevents other key processes required for normal growth.
So, having looked at the constituent parts, there are many contributing factors that may result in tea leaves being a poor choice of fertilizer across a number of plants.
Why Is Using Tea on Plants So Popular?
One of the main reasons that tea leaves are so popular is that it is a useful fertilizer in some cases. This is mainly because if a plant prefers soil with a pH level lower than that it is currently in (that is, it prefers a more acidic soil), then the application of tea leaves can create a more suitable environment for the plant to experience strong growth.
Using tea leaves is also a practice that has occurred for hundreds of years, and so it takes on a certain quality just by being a technique handed down through family stories and advice. These sorts of ”old wives’ tales” can stick in part because of the strong association that they can take on with positive family memories.
Which Types of Tea Is Best for Plants?
Another factor that is often overlooked by gardeners considering using tea leaves on their plants is the specific variety of tea they would be using. Tea comes in an increasing number of flavors; however, there are really only four main types of tea that come from the main tea plant species, Camellia sinensis. These are:
- Green tea
- White tea
- Black tea
- Oolong tea
As these different types of tea all come from the same plant, what is the difference between them? Well, it’s to do with the way in which they are treated. Each type of tea goes through different levels of a process called oxidization and fermentation in order to change the qualities of the final product, such as caffeination and flavor.
They are different levels of nitrogen and the relative proportions of other compounds based on the process it goes through, but also the way it was fertilized in light of the type of tea and the final result the manufacturers were looking to achieve.
It’s a safe bet to assume that the darker and more flavorful the tea, the higher the likelihood of a greater relative percentage of nitrogen versus phosphorus and potassium. As it’s been shown that having a greater amount of nitrogen available in the soil reduces the amount of aluminum that is taken up, you are likely to be better off sticking with darker teas to maximize the amount of overall benefit.
How Should Tea Leaves Be Applied to Plants?
There are a number of different ways that tea can be applied to plants. A few of the most common methods are:
- Tea leaf mulch
- Stewed tea
Tea Leaf Mulch
There are a number of different benefits to using mulching, and tea leaves are a good candidate for mulch.
Mulching is a process whereby a loose covering of material is spread across the top of the soil. This creates a lightweight seal over the soil. In applying this seal, the water retention of the soil is improved because there is less light that is able to reach the moist soil underneath, reducing the amount of evaporation that can take place.
Applying a layer of mulch also prevents the light from reaching the soil and can make a big difference in the ongoing battle against weeds. There are a few factors that influence a weed’s growth:
- Access to moisture
- Access to nutrients
- Acceptable temperature
- Access to light
While there is little that can be done for moisture, nutrients, and temperature, given that our own plants also require these things too, by starving the young weeds of light, their growth is significantly impacted. Mulching achieves this and can achieve similar results to many of the no-dig garden strategies that have been shown to be so effective against weeds.
In addition, a much layer of tea leaves will mean that decomposition of the tea leaves still has to take place, and the time this takes effectively acts as a slow-release fertilizer for the elements within the tea leaves that the plants may benefit from.
Stewing is the process and putting the leaves in water and allowing the flavor (via its chemical compounds) to escape into the water. Tea that has been stewed in water can expect to see a direct relationship between how long the tea has been left to stew and the volume of compounds released into the tea solution.
This means that for those not concerned about the contents of the tea and the impact that it can have on the soil (and, in turn, the plants), stewing tea will speed up the time taken for the compounds to be released into the soil. As with all use of water-based fertilizer, it’s important to ensure that the distribution of tea solution is carefully distributed to avoid imbalances in the soil.
As part of a regular addition of many different recycled kitchen foodstuffs, tea leaves can be a quality addition to compost. It can add a good source of nitrogen when given the time for it to be slowly broken down. Given some other components of tea that are not at all beneficial to plants, such as aluminum and fluoride, it should able be considered part of a broader healthy mix of compost ingredients.
When compost, including tea leaves, is applied, the length of time taken for it to break down thoroughly will be dependent upon the environment. As a general rule, it can be expected that in hot compost, the tea leaves should be left 6–8 weeks to break down, whereas, for cold compost, the process takes much longer — likely around 12 months to decompose fully.
When applying the compost, should be applied around the plant, working an inch of compost in with the top inch or two of soil and trying to retain as much of the soil’s existing structure as possible.
The Ideal Approach
Recommendations as to the best approach for almost all fertilizers lean towards slow and steady application, removing the risk of sudden changes to the soil environment for plants. Where sudden changes have occurred, it can be difficult to pinpoint the exact issues which are causing new problems with your plants.
This is no different when looking to decide on the optimal way to utilize tea in the garden. Composting is the most conservative way of using the tea’s beneficial compounds, and likely to be the most effective. Mulching is a strong second option, allowing time for tea to break down into the soil slowly. Stewed tea should be avoided due to the relatively aggressive way in which the balance of the soil may be altered.
Here is more on how to use tea leaves as natural fertilizers for all plants.
Using tea leaves is a technique that has been around for a long time and is not going anywhere. However, it’s important to recognize that understanding exactly what’s happening to the soil when you apply tea is critical to ensuring that it has the positive impact all gardeners want to see.