Give Old Washing-Up Sponges a Second Life in the Garden

While many kitchens have long since put a fresh sponge beside the sink, the old one has already ended up in the general waste. That is a pity. Gardening professionals now advise keeping certain worn-out sponges rather than binning them, giving them a second use outdoors. They can help save watering water, reduce drought stress and cut waste at the same time.

Why a washing-up sponge can make sense in a flower bed

Spring marks the start of a new season for balconies and gardens. Young plants produce delicate roots that can dry out quickly. The weather is often unpredictable too: a warm day may be followed by cold winds, while watering is not always regular.

This is exactly where a sponge's greatest advantage comes in: its porous structure. It absorbs surplus water before gradually releasing it again. In a pot, it acts as a small water store that supplies the roots for hours.

“A clean, suitable washing-up sponge in a pot can significantly extend the time between watering sessions – ideal in hot weather or during a short break away.”

Anyone with lots of window boxes, or who cannot water every day, will soon notice the difference. The compost does not dry out as rapidly, plants are less likely to develop drooping leaves, and sensitive young plants cope better with the crucial early stage.

Natural sponge or plastic? Which types are suitable

Before placing a sponge in compost, there is one key question: what is it made from? Not every type is suitable for the garden or compost heap.

These sponges are suitable for the garden

• Cellulose sponges: generally made from wood fibres, highly absorbent and biodegradable.
• Loofah sponges: made from dried gourd fibres and entirely plant-based.
• Other natural fibres: for example, blends of cotton and plant fibres (check the manufacturer's details).

After being thoroughly cleaned, these sponges can be added to compost or soil. They gradually break down, improve its structure and retain moisture within the system.

Take care with plastic sponges

The familiar yellow kitchen sponges with a green scouring layer are usually made largely from plastic. They can:

• release microplastics into the soil;
• give off chemical residues;
• remain unchanged in compost for years.

For this reason, these types do not belong in the compost heap. In some cases, they can serve as a temporary water reserve in large pots, but they should not be left there indefinitely and certainly should not be placed in a vegetable bed. Those who want to be completely certain should use natural varieties only in the garden.

How to sanitise a sponge before using it

A used kitchen sponge is a magnet for bacteria. It must be cleaned thoroughly before it goes near roots or into the compost. There are several options:

• Rinse it thoroughly under hot water until no foam or greasy residue is visible.
• Boil it in vigorously boiling water for several minutes.
• Treat it with vinegar: place it in a mixture of water and clear vinegar, allowing it to become fully saturated.
• Use a microwave: only with a damp sponge, for no more than two minutes on a high setting (be aware of the fire risk; never heat it when dry).

Afterwards, use the sponge solely for gardening or balcony purposes and never return it to the kitchen. This ensures that food remnants and washing-up liquid stay out for good.

Four practical ways a sponge protects your plants

1. A water store in a pot

This is probably the easiest approach: place the sponge in the lower section of a planter or window box.

• Add a layer of expanded clay or broken terracotta for drainage.
• Lay one or two sponges flat on top of the drainage layer.
• Fill with compost and plant as usual.

When watering, the sponge takes up excess water that would otherwise drain out from the bottom. When conditions are dry, its fibres release the stored moisture back into the compost. Windy balconies benefit especially, as pots there often dry out particularly quickly.

2. A moisture booster for compost

Compost needs three things: air, enough moisture and a good balance between nitrogen-rich and carbon-rich materials. Natural sponges help in several ways.

Cut into small pieces, they provide:

• improved moisture distribution throughout the compost heap;