Feeding Potted Plants: What to Do in the First Month After Repotting

The most common fertiliser mistake is not strength, it is timing. A plant that has just been moved, unpacked from a transport box, or repotted into new mix has a root system with broken tips on it. Those tips are where water and nutrients enter, and they are also the surface through which salt does its damage. Feed a plant in that state and you pay for the injury.

The first month after you bring a plant home

Hold off. Not entirely, and not forever, but the first round should be weak. If the plant came out of a market stall, its roots were disturbed and its top was probably handled more than it liked. Feed at roughly one quarter to one fifth of the normal organic strength, and only after it has settled for a week or two in its new light.

What the plant needs in those weeks is water discipline, not nutrition. Roots regrow faster in a mix that is moist and aerated than in a soggy one, and a feeding programme cannot compensate for a root system that is suffocating. Every one of these failures looks like hunger, which is why people fertilise their way out of it in the wrong direction.

Spring: the main feed

Growth starts and the plant needs building material. Work in a balanced organic fertiliser at the point where new roots will meet it, keeping it below about two centimetres of soil depth so it is not sitting against the crown, then water. In a pot, that means a layer of mix, the fertiliser, more mix, and never a ring of concentrated material against the stem.

Repeat lightly about once a month through the growing run rather than giving one heavy dose. A pot holds a small volume of soil with no way to buffer excess salts, which is exactly the difference between a bed and a container. Loosen the surface between feeds so water reaches the mix instead of running down the side of a compacted ball.

Summer: dilute, and less than you think

Warm weather and fast growth call for nitrogen, and nitrogen is the form that burns easiest. Dissolve it in the watering can and apply it weak and often. High temperature also means the mix dries between waterings, and salts left behind by evaporation concentrate at the dry edge of the root ball. Water through with plain water now and then.

Plants that stall in the worst heat, the succulents and many mediterranean herbs, should not be fed at all during that stall. See why autumn is the season that pays for those. A feeding schedule that ignores dormancy is a schedule that damages plants.

Autumn: potassium, and stop early

Autumn feeding has one job: hardening. Potassium is the nutrient associated with it, and the aim is a plant that goes into winter with ripe growth rather than soft, sappy shoots that blacken at the first frost. Same dilute-and-water method as summer.

Stop while there is still time for the growth to firm up. A late feed pushes new soft growth that winter will kill, and the plant loses both the shoots and the reserves they were made from.

Winter: almost nothing

Low light and cool temperatures slow uptake to a crawl. Fertiliser applied to a winter houseplant accumulates in the mix unread, and what you are then fighting in February is white crust on the surface and brown leaf tips. Feed only plants that are genuinely growing under lights or in a warm bright room, and skip the rest.

The exception is a plant that is obviously depleting: pale new leaves on a plant that has been in the same mix for two years. That is a shortage, and it deserves a weak feed even in winter. A plant that is simply not growing does not.

Three rules that outlive any schedule

• Never let granular or concentrated fertiliser sit on the soil surface where it can be pressed against a stem or a shallow root when you water. Bury it lightly or dissolve it. Surface salts are how a careless month turns into a root-tip burn.
• Foliar feeding works, and it is a supplement. A dilute spray taken in through the leaves gives a quick response in a plant whose roots are not doing their job, which is useful, and it does not replace a root programme for anything you intend to keep for years.
• Feed a plant that is thirsty and you risk the burn; water first, feed after. In dry mix, the solution cannot move, and the highest local concentration is exactly where the damaged tissue will be.

There is a related question that decides more than the schedule does: whether you are using a slow organic material or a fast soluble one. The difference between organic and inorganic fertiliser is mostly a difference in how often you have to think about it, and a potted plant with a long season ahead does well on a combination of the two.