How to top dress pots and beds with fertiliser

By Joe Barrington, founder of Dr Forest · Published October 2024 · Updated 10 October 2026

Top dressing means scattering dry fertiliser on the surface, scratching it in and watering it. You do not unpot the plant or dig the bed. It is the simplest way to feed, and the one most people get wrong by guessing the amount.

What top dressing is

A slow-release organic fertiliser is made of plant and mineral meals that soil life has to break down before the plant can use them. That is why it goes on the surface and gets watered in rather than dissolved in a can: the water carries it into the top few centimetres, where the roots and the microbes that feed them are most active. One dressing then keeps working for several weeks. A liquid feed wants you back every Sunday. A top dressing does not.

The rate is the whole skill. Too little and nothing happens. Too much, or a pile left against a stem, and you get scorched roots and salt-crusted compost. The numbers below are for All Purpose 4-4-4, which is the bag most people top dress with. Other Dr Forest bags carry their own rate on the label.

How much to use

In pots, the dose follows the volume of compost, not the size of the plant. The litres are printed on the compost bag or the pot. If you do not know, fill the empty pot from a 10-litre bucket and count. Then weigh the fertiliser on kitchen scales, or use the tablespoon guide: a level tablespoon holds about 12 to 15 g.

Pot rates are per litre of compost in the pot. Do not use them on beds. Feed every two weeks only in thin, sandy compost, or if the leaves are evenly pale.

Worked example. A 30-litre pot of a heavy feeder, top dressed at 4 g per litre: 4 × 30 = 120 g. That is eight to ten level tablespoons, every three to four weeks.

The three steps

1. 1

   Weigh it out

   Measure the dose for the pot or the area. If you want to cut the dust, mix the fertiliser with an equal amount of worm castings, compost or damp coir. Weigh the fertiliser first; the castings are extra and do not count towards the dose. Do the mixing outdoors.

2. 2

   Scatter and scratch it in

   Spread it evenly over the surface, then work it lightly into the top centimetre or two with your fingers or a hand fork. Keep it 5 cm clear of stems and off the crown of the plant.

3. 3

   Water it in

   In pots, water in about a tenth of the pot's volume: 3 litres for a 30-litre pot. In a bed, give it a good soaking, about half a 10-litre can per square metre. The water carries the feed into the compost and wakes the soil life that releases it. Plain water, tap or rain, is all it needs.

If you like to add biology when you water in, EM-1 as a drench, or a compost extract such as Soilsmiths' Goop, is a reasonable extra. If you brew your own compost tea for anything you will eat, leave the molasses out; it can feed harmful bacteria in the brew. None of these are required. Water is.

When to switch to a bloom feed

Once tomatoes, peppers and other fruiting crops start to flower, swap All Purpose for Bloom 2-8-4 at 3 to 4 g per litre of compost every 3 to 4 weeks. Use one or the other, not both. On beds, Bloom goes on at about 100 g per square metre once. It is rich in phosphorus, so it is not a feed to repeat every few weeks on open ground. For tomatoes specifically, the season plan is in best fertiliser for tomatoes.

A liquid feed can sit alongside a top dressing, but it is a top-up, not a second base. If you are already top dressing at the rates above, add a liquid only when the leaves tell you to: evenly pale for nitrogen, yellow between the veins for magnesium. The reading is in why tomato leaves turn yellow.

Three mistakes that scorch roots

• Guessing the amount. A "generous handful" on a 10-litre pot is two or three times the rate. Weigh it the first few times, then you will know what the right amount looks like.
• Leaving a pile against the stem. A concentrated patch of fertiliser against the crown burns it. Scatter evenly, keep it clear of the stem, scratch it in.
• Feeding dry compost and not watering in. Concentrated feed in dry compost pulls water away from the roots. Water the pot first if it is dry, dress it, then water again.

Top dressing suits any slow-release meal: the organic slow release guide covers how those meals release, and the organic fertiliser range carries the rate for each bag on its label.

Frequently asked questions

How much fertiliser do I top dress a pot with?

For All Purpose 4-4-4, 2 to 4 g per litre of compost in the pot: 2 g for light feeders such as herbs and beans, 3 g for salads and most flowers, 4 g for heavy feeders such as courgettes and hanging baskets. A level tablespoon holds about 12 to 15 g. A 30-litre pot of a heavy feeder takes about 120 g.

How often should I top dress?

Every 3 to 4 weeks for medium and heavy feeders in pots, every 5 to 6 weeks for light feeders, and every 4 to 6 weeks on beds. Only go to every two weeks in thin sandy compost or when leaves are evenly pale.

Do I need to water a top dressing in?

Yes, always. In pots, water in about a tenth of the pot's volume. On beds, about half a 10-litre can per square metre. The water carries the feed into the root zone and starts the soil life that releases it. Dry fertiliser sitting on dry compost does nothing and can scorch.

Can I top dress and use a liquid feed at the same time?

You can, but treat the liquid as a top-up rather than a second base. If you are dressing at the rates on this page, add a liquid only when the leaves show a specific shortage.

Should I top dress with All Purpose or Bloom?

All Purpose 4-4-4 for leafy growth and general feeding. Switch to Bloom 2-8-4 when fruiting crops start to flower. Use one or the other, not both at once.