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HydrangeasThe internet is full of tips on feeding houseplants with sugar, yeast or coffee grounds. Some of them really help, others are useless and a few can do harm. Here is when houseplants need feeding, which natural fertilisers work and how to avoid overfeeding.
When houseplants need feeding
A potted plant has only a small volume of soil, and a few months after repotting its nutrients run out. So during active growth — from spring to late summer — most houseplants are fed every 2–4 weeks. In autumn, feed less often, and in winter, when growth slows down, usually stop altogether.
Signs of nutrient deficiency:
- slow growth and small new leaves;
- leaves turning pale or yellow, starting with the lower ones;
- flowering plants failing to set buds;
- weak, stretched stems (though this can also be caused by lack of light).
Don't feed a plant right after repotting (wait 4–6 weeks), when the soil is bone dry (water it first) or when it is sick or has just arrived in your home.
Natural fertilisers that work
Worm castings and compost
The best natural fertiliser for houseplants is worm castings (vermicompost) or mature compost. Mix them into the potting mix when repotting or spread a thin layer on the surface; liquid vermicompost is diluted for watering according to the instructions. This kind of feeding is gentle and hardly ever burns roots.
Wood ash
Ash contains potassium, calcium, phosphorus and magnesium and suits flowering plants well. Stir 1 tablespoon of sifted ash into 1 litre of water and use it once a month during the growing season. Important: ash makes soil more alkaline, so don't use it for azaleas, hydrangeas, camellias and other acid lovers. Only use ash from clean wood, grass or straw — never from barbecue charcoal, firelighters, painted wood or rubbish.
Plant foods with doubtful benefits
Coffee grounds
Used coffee grounds contain a little nitrogen and loosen the soil. But fresh grounds added straight to a pot soon go mouldy, form a crust and attract fungus gnats, and caffeine can slow the growth of some plants. Contrary to popular belief, used grounds hardly acidify soil. They are best added to compost; in pots, use only small amounts, well dried and mixed into the soil.
Citrus peel infusion
An infusion of orange or lemon peel contains very few nutrients, so it cannot replace fertiliser, and its sweet smell attracts fruit flies. If you want to use peel, put it in the compost.
Myths: sugar and yeast
Sugar. Plants make their own sugars in their leaves through photosynthesis, and roots don't take up sugar solution as food. Sugar in the soil feeds mould, bacteria and flies. So "sugar feeding" does more harm than good.
Yeast. A yeast solution stimulates soil microorganisms but contains almost none of the nitrogen, phosphorus and potassium plants need and cannot replace a proper fertiliser. In a pot it can make the soil sour and smelly.
How to avoid overfeeding
- Dilute fertilisers more than the label says — little and often is better.
- Only feed plants when the soil is moist.
- A white crust on the soil and dry brown leaf tips are signs of excess salts: flush the pot with plenty of water and take a break from feeding.
- For most plants, ready-made liquid houseplant fertilisers are the easiest option: they are balanced and their composition is on the label.
FAQ
Can I water plants with sugar water?
Better not: roots can't use sugar, and in the soil it encourages mould and flies.
What is the best natural fertiliser for houseplants?
Worm castings or mature compost, and for flowering plants that dislike acidic soil, a wood ash solution.
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Author: Maria Svitlovir
Graduated from Taras Shevchenko National University of Kyiv, Institute of Biology and Medicine (2001). BSc in Biology, MSc in Horticulture. Writes about plants, works at a garden centre selecting and repotting plants, and contributes to plant reference guides.
