Don’t Throw Away Your Used Tea Bags — Try My Grandma’s Plant Trick Instead

My grandma is of Scottish and English heritage. As such, she drinks lots of tea. Her favorite cup is plain English Breakfast: no milk or sugar, which she calls “nude.” But instead of tossing her teabags, she has a surprising gardening hack that she’s passed down through the generations: putting used tea bags in her plants. 

Among other benefits, she tells me, used tea bags contain nutrients that enrich the soil, and their tannins lower soil pH. Her home and mine are full of thriving plants and flowers, thanks in part to this trick. But is it safe to put used teabags in potted plants, and does it really work? Here’s a foolproof guide to boosting plants with steeped tea.

My grandma has the greenest thumb of anyone I know, so I rarely question her gardening advice. But is there actually science behind this trick? Here are a few evidence-backed ways steeped tea can help your plants thrive.

Soil pH, or how acidic or alkaline your plants’ soil is, plays a huge role in their ability to thrive. For plants that prefer acidic soil, such as azaleas, hydrangeas, and indoor ferns, tea bags can naturally lower soil pH by steeping tannins into the soil. You may have heard of tannins in reference to wine, but they’re also present in tea — especially black tea. 

As tea breaks down, it releases tannic acid into the soil, increasing soil acidity over time. The decomposition process itself also contributes to increasing soil acidity. Tannic acid is highest in used teabags, so it’s best to add the soaked leaves post-tea time. 

Fertilizer helps plants grow by adding crucial nutrients to the soil, including nitrogen, phosphorus, and potassium (often abbreviated to NPK on store-bought fertilizer). As organic matter breaks down, it releases these elements, along with other nutrients such as magnesium, calcium, and sulfur.

Tea leaves are an easy way to naturally fertilize your soil. As they decompose, they release small amounts of nitrogen and minerals, which help keep roots healthy. If you use compost as fertilizer, adding tea bags to your pile can enhance its benefits, and steeped tea between fertilizing can add a little boost.

If you’re dealing with pests like fungus gnats, ants, or even slugs, tea can help. Many types of tea contain natural essences, such as cinnamon and peppermint, that repel insects. But plain black or green tea is also helpful on its own, as it helps mask the scent of soil that many pests are drawn to.

Peppermint tea is especially effective for ants and gnats; the menthol in peppermint is a known insect repellant. Other pest-repelling essential oils found in tea include bergamot (in Earl Grey), lavender (in many chamomile blends), lemon, and other citrus oils.

Whether it’s safe to add tea bags to soil depends on what they’re made of. My grandma always threw her tea bags into her plants. That said, plastic leaching into soil is a real concern and can harm soil health. Plastic doesn’t break down easily, which will interfere with the tea’s decomposition and fertilization benefits. 

Rule of (green) thumb: If the bag is pure white and you can’t tear it, remove the tea before adding it to your garden. When in doubt, empty the tea from the bag before adding it to your plants. If your tea bags are made from a naturally biodegradable material, such as paper, cotton, or other plant fibers, it’s fine to put them directly in the soil. Some tea brands I love with non-toxic bags include Traditional Medicinals, Pukka, and Numi Organic Tea.

While most houseplants prefer slightly acidic soil, not all do. Before adding tea bags to your plants, confirm whether they prefer alkaline, acidic, or neutral soil. 

Most houseplants, like snake plants, ZZ plants, ferns, spider plants, orchids, and peace lilies, tolerate neutral to slightly acidic soil. Opt for moderate amounts of black tea — Assam, Darjeeling, Ceylon, English Breakfast (usually a blend), and Earl Grey (black tea with bergamot) — with these plants. 

Blueberries, azaleas, and camellias are examples of outdoor plants that prefer highly acidic soil. For these plants, you can use black tea or herbal teas with fruit essences that repel insects. 

Plants that prefer alkaline soil — to which you should not add highly tannic tea — include most herbs and vegetables, plus some ornamentals like lilacs and geraniums. For any plants that like neutral soil, it’s best to use a tea with lower tannin levels like green tea. 

It’s best to use one to two tea bags per small plant, as too much can alter the soil pH too quickly or drastically. Here’s how to add tea bags to your plant.

• Remove your steeped tea bag from your water before adding any milk, sugar, or honey; these can attract pests or cause mold.
• Let it cool to room temperature. Hot tea (like hot water) can damage roots.
• Your first option is to empty the tea leaves from the tea bag and mix them into your soil while they’re still wet. Dispose of the used tea bag.
• Your second option is to remove the tag and staple from your tea bag (if it has one), then throw the whole bag into the soil. This is the way my grandma did it.
• Depending on the plant and how much soil it has, repeat once every other week to once per week.