How Often Should You Fertilise Container Plants?

Container gardening offers enormous flexibility — crops and plants can be grown in the smallest of spaces. But it comes with one significant challenge: containers exhaust their nutrients far faster than garden beds. Every time you water, nutrients leach out through the drainage holes. Most potting composts run low on nutrients within six to eight weeks of planting. Without regular feeding, container plants hit a wall and stop growing well.

Why Containers Need More Feeding Than Ground Soil

In a garden bed, plant roots can extend outward through metres of soil, accessing a large reservoir of nutrients from decomposing organic matter, soil minerals and microbial activity. In a container, roots are confined. The volume of compost is limited, it dries and re-wets repeatedly with watering, and nutrients flush through quickly. Even with a premium slow-release compost, plants in containers growing actively in warm weather will typically need supplemental feeding from about four to six weeks after potting.

The Two Main Approaches

There are two ways to manage container nutrition, and most experienced container gardeners use both:

• Slow-release granules mixed into the compost: blend controlled-release fertiliser granules (like Osmocote) into the compost before planting. These feed steadily for three to six months and greatly reduce the labour of liquid feeding. Still best supplemented with occasional liquid feeds for heavy-feeding crops.
• Regular liquid feeding: diluted liquid fertiliser applied every one to two weeks through the growing season. More labour-intensive but gives precise control and allows you to adjust the feed type as the plant's needs change.

Frequency Guidelines for Different Plant Types

• Tomatoes and peppers in containers: every 7–10 days with a high-potassium tomato feed once flowering begins; fortnightly before that with a balanced feed
• Herbs: monthly with a balanced liquid feed; most prefer lean conditions and over-feeding reduces flavour
• Flowering bedding plants: fortnightly with a balanced or high-potassium liquid feed
• Shrubs and perennials in large pots: monthly in the growing season with a balanced granular or liquid feed
• Leafy salads: fortnightly with a nitrogen-leaning balanced feed; stop one to two weeks before harvest

Signs Your Container Plants Need Feeding

Pale yellow lower leaves, stunted growth, very small new leaves and poor flowering are all signals that nutrients have run out. Do not wait for these signs — by the time they appear the plant has already been restricted for some time. Set a regular feeding routine from the start and stick to it through the season.

Refreshing Old Compost

For perennial plants in pots that are not repotted each year, remove the top 5 cm of old compost each spring and replace it with fresh compost mixed with slow-release granules. This refreshes the nutrient supply without the upheaval of full repotting.