Compost

Compost is organic matter, such as food scraps, coffee grounds and dry leaves, that has broken down into a dark, crumbly material rich in nutrients and beneficial microbes. Mixed into potting mix, it improves nutrient content, helps the mix hold moisture more evenly, and supports the soil biology that keeps container plants healthy over multiple seasons, rather than acting as a fast-release fertilizer on its own.

On a balcony, making compost usually means a small, enclosed bin designed for tight spaces, since a traditional open compost heap is not practical without a yard. These compact systems break down kitchen scraps and light yard waste into finished compost over some weeks to a few months, and well-managed bins produce little to no odor, which matters when neighbors are close by on either side.

When using homemade or store-bought compost, mixing it into potting mix rather than using it alone as a growing medium gives the best structure, since pure compost alone can compact and hold too much water in a container. A common mistake is adding unfinished compost, still warm or with recognizable food scraps, directly around plant roots, which can stress or even burn young plants until it fully finishes breaking down.