Tea drinkers who enjoy dabbling in a bit of casual green thumbery are most likely aware that used tea leaves are a beneficial addition to garden beds.
Whether applying used tea directly under your plants as mulch, or throwing them atop your compost, used leaves are an excellent way to supplement the nutritional needs of your garden.
While many people swear by used tea leaves as a source of plant food, it is worth noting that a lot of claims on the ways that tea should be used in gardening may indeed be myths.
One of the nutritious elements that tea has to offer is nitrogen, which is essential to plant nutrition as it is the building block of amino acids. Amino acids, in turn, make up proteins, which are responsible for performing a number of important functions in organisms, which results in leafy growth for plants. However, once tea leaves are spent, they contain very little of the components they originally had, with all the goodness already enjoyed from a cuppa.
Some sources suggest that watering your plants with brewed tea once in a while can be beneficial so as to reap the full benefits of the leaves. However, Gardening Which magazine discredits this tip by putting forth the fact that tea contains trace minerals like aluminium, fluorine, and manganese, which, although are harmless to humans, could actually impair plant growth. This is particularly evident if applied in high concentrations from strongly brewed tea. An occasional liquid feed is a better option for plant health.
Another belief is that used tea leaves are best applied to plants that require lower pH levels in the soil. Some gardeners suggest that tea is best used on acidic soil lovers including rose bushes, hydrangeas, azaleas, blueberries, and beans, just to name a few. This theory stems from the understanding that tea contains tannic acid. It does not.
Tea does, however, contain tannin, which are a broad class of compounds, which is what gives black tea its colour and astringent properties. Tannic acid is just one type of tannin and the tannins in tea do not include tannic acid. Gallic acid is in fact the base unit of tea tannins. As a result, black tea does sit on the slightly acidic side of the pH scale. But again, once leaves have been steeped, they generally lack most of their original substance and have no profound effect on the pH levels of soil.
Used tea bags can also be just as beneficial in supplementing the organic matter you feed your garden. Yet what many people tend not to realise is that not all tea bags are biodegradable and end up just sitting in the soil or compost heap, waiting to be picked out and disposed of.
Tea bags that contain a polypropylene coating will not break down and should be discarded. While the tea bag may not be environmentally friendly, the tea leaves or fannings inside the bag can still be used in the garden; simply tear the bag open and remove the leaves. This isn’t to say that all tea bags aren’t biodegradable with ones made from paper or silk perfectly acceptable for throwing into the compost or burying in the garden. Biodegradable tea bags will usually let that detail be known on their packaging.
The main benefits of applying tea directly to your garden bed as mulch is that it helps in impeding weeds and retaining soil moisture. Retaining moisture is good for areas of exposed soil that may dry out too quickly, preventing root systems from absorbing enough water. Take care when applying tea directly to edible plants because while there is not much conclusive evidence in this claim, one source suggests that using tea during the active growth of vegetables could affect their flavour. One could assume that if used tea leaves cannot transfer much of their original nutritional content to a garden, then very little flavour could be transferred either — something to consider anyway.
What should probably be taken from all of this information is the fact that used tea leaves should not be considered as a kind of magical fertiliser. Although drinking tea does amazing things for our bodies, once steeped, they don’t have a lot of specific properties that can be applied to plant growth.
In reality, used tea leaves sit in the realms of food waste, with many gardeners even bypassing their use as mulch. As a result, gardening experts suggest just adding used tea leaves to the compost heap where the worms can make the most of their organic matter. This is a great way to get more out of your tea leaves, long after you've stopped using them for your cuppa.