Fertiliser instructions fail because they name a plant instead of two numbers. Dose is concentration multiplied by volume, and this guide gives both: grams per litre of water, then litres of solution by pot diameter. It also covers how often to feed, what an overdose does inside the root zone, how to reverse one, and where the standard dose needs adjusting.
Dose by the litre of water
Mix soluble fertiliser at 1 g per litre for a standard feed, or 0.5 g per litre if you feed weekly. A 20 percent nitrogen product at 1 g per litre delivers 200 mg of nitrogen per litre, which is 200 ppm, the concentration commercial nurseries run for foliage plants in active growth.
That arithmetic is worth carrying, because it lets you read any label. Take the nitrogen percentage and multiply by 10 for the ppm delivered per gram per litre. A 30 percent nitrogen feed at 1 g per litre gives 300 ppm, which is too strong indoors, so the same product wants 0.65 g per litre to land in the same place.
Liquid concentrates follow the same logic in different units. A concentrate listing 7 percent nitrogen at 5 ml per litre delivers 350 mg of product per litre, of which 24.5 mg is nitrogen. It sits well below powder strength and suits weekly feeding.
How much solution a pot takes
Solution volume scales with pot diameter faster than people expect, because volume follows the cube of the width. To wet a root ball through with a little run off: 300 ml at 15 cm, 700 ml at 20 cm, 1.4 litres at 25 cm, 2.4 litres at 30 cm and 5 litres at 40 cm.
Multiply the two numbers for the actual dose. A 15 cm pot fed at 1 g per litre receives 0.3 g of fertiliser. A 40 cm pot fed at the identical concentration receives 5 g, sixteen times as much, out of the same jug. Dosing per plant leaves small pots starved and large ones burnt in one room.
Run off is part of the method rather than waste. Mixing enough to produce 10 to 20 percent run off means the whole root ball sees one concentration, and it carries the last feed's residue out of the pot on the way. Throw away whatever collects in the saucer, or the pot draws it straight back up.
How often to feed
Feed actively growing indoor plants once a fortnight at 1 g per litre, or weekly at 0.5 g per litre, which delivers a similar total with less swing at the roots. Feed through the October to May growing months in the UAE and pause through the summer peak, when growth has stalled anyway.
Growth decides frequency, not the calendar on its own. A plant pushing out a new leaf every fortnight is spending nutrient and needs it replaced. A plant that has done nothing for 8 weeks is not consuming what is already there, and adding more raises the salt concentration around roots that have stopped drinking.
Newly potted plants need nothing for 6 to 8 weeks, because commercial mixes carry a starter charge covering that period. Feeding on top of it is the commonest overdose in a UAE home, and it lands on roots still recovering from the move.
What an overdose does, and how to reverse it
An overdose does not poison a plant chemically. It raises the salt concentration of the soil solution above the concentration inside the root cells, which reverses the osmotic gradient and pulls water back out of the roots. The plant wilts in wet soil, so the owner waters more and speeds the whole thing up.
Four symptoms turn up in order across 10 to 14 days. A white crust appears on the soil surface. Leaf edges brown and go crisp. The plant wilts in moist soil. Then the lower leaves drop. Catch it at the crust and nothing lasting has happened. At leaf drop you have root loss that takes a season to rebuild.
Reverse it by flushing. Pour 3 to 4 pot volumes of plain water slowly through the container, let it drain fully, then repeat the next day. Feed nothing for 8 weeks afterwards and keep the plant out of direct sun, because damaged roots cannot supply a plant under a full light load.
Adjusting the dose to the plant
Three groups need the standard dose changed. Cacti and succulents take a quarter of it. Flowering plants take the standard dose at a different ratio. Newly bought plants take none at all until they have settled for 6 to 8 weeks in the position you want them in.
Slow growing species follow their growth rate rather than their size. A large slow plant uses less nutrient than a small fast one, so a 40 cm pot holding a slow palm still takes its 5 litres of solution but at half the concentration, which supplies the same total across two feeds instead of one.
Water quality shifts the arithmetic in the UAE, since the minerals already in the tap water add to whatever salt load the fertiliser creates. Anyone feeding a mixed collection of indoor plants gets steadier results by dropping to 0.5 g per litre weekly and flushing every second month than by feeding at full strength and hoping the pot clears itself.
FAQ
The arithmetic behind a feed sits in 3 answers. Strength per litre of water, how often to repeat the feed, and what actually happens inside a pot once the dose has gone too high.
How much fertiliser per litre of water?
One gram per litre of a balanced soluble feed on a fortnightly schedule, or 0.5 g per litre weekly. On a 20 percent nitrogen product, 1 g per litre works out at 200 ppm nitrogen, which is the working concentration for foliage plants in growth.
How often should plants be fed?
Fortnightly at full strength, or weekly at half strength, through the October to May growing months, and not at all through the summer peak while growth has stalled. Skip feeding altogether for the first 6 to 8 weeks after potting a plant.
What happens if you overdose fertiliser?
Salt concentration outside the roots rises above the concentration inside them, so water moves out of the plant instead of in. It wilts in wet soil, leaf edges go crisp and the lower leaves drop. Flush with 3 to 4 pot volumes of plain water on two consecutive days.