Soil and watering
Wetting agent rates and coverage: how much to use per square metre
Water that runs off a bed and puddles on the path has not watered anything. It has just moved.
Made by Dr Forest
Natural Wetting Agent
100 m² of soil from a 500 ml bottle
- One bottle covers beds, borders, lawns, pots and compost
- Six ingredients, including organic soap nuts and aloe vera
- Handcrafted in small batches in Stockport
A soil wetting agent is a surfactant. It lowers the surface tension of water so that water spreads through soil that has turned water-repellent, rather than sitting on top of it or running off the surface. This page is the practical end of that: how much to use, how far a bottle goes across a garden, and where it will make no difference at all.
Dr Forest makes a natural soil wetting agent handcrafted in small batches in Stockport. It has six ingredients: organic Indian soap nuts (Sapindus mukorossi), aloe vera grown in-house in Stockport and harvested fresh for each batch, vegetable glycerine, citric acid, potassium sorbate as a food-grade preservative, and reverse osmosis water. For the background on what these products are and how they work, read what a wetting agent is.
In short
- Rate is 2.5 to 5 ml (0.5 to 1 teaspoon) per litre of water, applied at 1 litre of solution per square metre.
- 500 ml covers 100 m² at 5 ml per litre. That is most of a small back garden in one bottle.
- It only helps where soil is actually water-repellent. Test first with a cup of water.
- It is not a fertiliser and it does not hold water in the soil. It changes how water moves.
Made by Dr Forest
Natural Wetting Agent
- 100 m² of soil from a 500 ml bottle
- Works as a soil drench or a foliar spray
- Six ingredients, including organic soap nuts and aloe vera
- Handcrafted in small batches in Stockport
| Covers | 100 m² from 500 ml |
| Cost per m² | From 8p |
| Sizes | 500 ml · 1 L · 5 L |
One bottle, these jobs
- Beds and borders
- Raised and veg beds
- Lawns and dry patch
- Under trees and shrubs
- Pots and containers
- Hanging baskets
- Peat-free compost
- Greenhouse borders
- Seed trays and modules
- Allotment plots
- Foliar sprays
- Reviving a dried-out compost bag
Use as a soil drench at 2.5 to 5 ml (0.5 to 1 teaspoon) per litre, or in a foliar spray at 5 to 10 ml per litre.
View the wetting agentFree UK delivery over £40
Test before you buy anything
Water-repellent soil is a specific condition, and a surfactant does nothing useful on soil that does not have it. The test takes a minute.
Untreated
Water beads and runs off
With a wetting agent
It spreads and soaks in
- Clear any mulch or leaf litter so you are looking at bare soil.
- Pour a cupful of water slowly onto the surface and watch the first ten seconds. Soil that is simply dry darkens and takes the water down. Water-repellent soil holds it in beads, or lets it run sideways and soak in somewhere else.
- Scrape down two or three centimetres and repeat. Repellency is often a surface skin over damp soil beneath, which is exactly why watering from above stops working.
Sandy soils and beds with a lot of undecomposed organic matter on top are the usual candidates. So are containers and beds that have been allowed to dry right out, and ground under established trees and shrubs where rainfall rarely reaches.
How much to use
Application rate
The rate, in one line
The dilution does not change with the job. What changes is how much solution you make.
2.5 to 5 ml
Concentrate
1 L
Water
1 m²
Treated
Scale it straight up. At 5 ml per litre, a 9 litre watering can takes 45 ml of concentrate and covers 9 m².
| Use | Dilution | Applied at |
|---|---|---|
| Soil drench | 2.5 to 5 ml (0.5 to 1 teaspoon) per litre | 1 litre of solution per m² |
| Foliar spray | 5 to 10 ml per litre | Until leaves are wetted |
Dr Forest Natural Wetting Agent application rates.
Fill the can, add the concentrate, agitate it gently rather than shaking it into a head of foam, and apply.
The guide below works out the dose for a lawn, a bed, pots, a leaf spray, planting, or a dried-out compost bag. It uses the rates on the bottle.
How-to guide and calculator
Wetting agent for lawns, pots and outdoor beds
Use it on lawns, pots and outdoor beds when water beads, sits or runs off instead of soaking in. Mix Dr Forest Natural Wetting Agent at the rate on the bottle.
ml means millilitres (5 ml is one level teaspoon). L means litres. m² means square metres — a 3 m by 1 m border is 3 m². “From the bottle” is the concentrate. Mix it into water before you pour.
Do you actually need one?
The cup-of-water test
Use it where water will not soak in: it sits in beads, runs sideways, or races out of a pot while the middle stays dry. Lawns, pots and outdoor beds all qualify. A dry spell is one of those times, not the only one. A brown lawn can also be grubs, disease, or animal urine. Pull a tuft: if the roots are gone, a wetting agent will not bring that patch back.
Calculator
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250 ml
from the bottle, for this watering · 50 tsp
Bottle to buy
1 × 500 ml
Mixing and method
How to apply a wetting agent
-
Shake the bottle
The working ingredient is soap-nut extract. It settles. Shake before you measure. Rainwater gives it an easier time than hard tap water.
-
Measure from the bottle
One level teaspoon is 5 ml. Start at 2.5 ml per litre for soil and pots, and move up only if water still beads. Lawn is 5 ml per litre. Leaf spray starts at 5 ml per litre, up to 10.
-
Add to water first
Fill the can, add the wetting agent, stir gently. If you are adding a leaf feed, mix the wetting agent in before the feed. Use a made-up mix the same day.
-
Apply slowly, in the cool of the day
Early morning or evening, not strong midday sun. A watering can with the rose (the sprinkler head) on beats a hose. Poured on fast, the mix runs off exactly as plain water does. On leaves, wet both sides and keep the spray off open flowers while bees are working.
-
Water it in
On lawns and bare soil, follow with plain water so the mix moves into the thatch and towards the roots. The bottle says about another litre per square metre. Do not flood a dry patch: water that cannot get in simply runs to the path. On pots, water in stages. A tray can catch runoff, then tip it out after a few hours so the compost does not sit soggy.
-
Judge it on water, not colour
The next watering should sink in where it previously beaded. Green-up on a lawn is slower, over a week or two, and only where the grass is still alive at the base. Dead turf needs reseeding once the soil is taking water.
9 litre can
45 ml
At 5 ml per litre — nine teaspoons — covering 9 m² of lawn or border.
5 litre can, pots
12.5–25 ml
2.5–5 ml per litre. At the top of the range that wets about five 10-litre pots.
| Job | How much from the bottle | How to put it on |
|---|---|---|
| Lawn | 5 ml per litre (1 tsp) | 1 litre of mix per square metre |
| Beds, borders, raised beds | 2.5–5 ml per litre | 1 litre of mix per square metre |
| Pots and hanging baskets | 2.5–5 ml per litre | Until the pot feels heavier |
| Leaf spray | 5–10 ml per litre | With a foliar feed or biostimulant, morning or evening |
| First watering at planting | 2.5 ml per litre | Once, when you plant |
| Dried compost bag | 5 ml per litre | About 5 litres of mix per 50 litre bag |
Lawn
Lawn dry patch
The usual case is dry patch: the soil underneath stays bone dry, water beads or runs off, and the grass does not recover when rain returns. A dry spell is another time to use it. Water that would bead or run off soaks in more evenly and can go deeper, so the root zone stays wet longer than if that water ran away. It does not add a store of water, and it does not replace the next watering. Leatherjackets, disease, spilt fuel and animal urine also leave brown patches. If the grass lifts with no roots, look for grubs before you buy a bottle.
01
Spike densely
The Royal Horticultural Society says make plenty of holes with a fork so water has a way in. Scarify thatch in autumn, and aerate so the lawn is less prone next year.
02
Little water, often
Apply some water each day for a few days. A heavy soak on repellent ground runs off. The bottle’s own water-in is about another litre per square metre, not a flood.
03
Repeat the programme
RHS advice is to repeat that treatment monthly for three to four months, with the spiking and watering. A wetting agent goes alongside it. One dose rarely clears an established patch.
This bottle’s lawn rate is separate from the RHS method: 5 ml per litre, put on as 1 litre of mix per square metre. A 500 ml bottle covers 100 m² at that rate. If the grass has died, reseed once the soil takes water. In severe cases that still will not rewet, the RHS says the turf and the top 8–10 cm of soil may need replacing.
On a dry lawn, water in with about another litre of plain water per square metre so the mix can move down. Do not flood it: water that cannot get in runs to the path. A 2025 trial on a sand golf green found that watering a surfactant in straight away worked better in late summer than waiting. That was golf turf and a different product, so the bottle rate stays 1 litre of mix per square metre.
Calculate a lawn doseContainers
Pots and hanging baskets
You water the pot, the water is out of the drainage holes in about two seconds, and the root ball is still dust dry. The water found the gap between compost and pot wall. Start at 2.5 ml per litre and move to 5 ml only if it still runs through. If the compost has shrunk away from the sides, water once with plain water first so the mix does not run down the gap. Then water the compost, not the leaves, in stages. A tray can catch what runs out; tip it away after a few hours so the pot does not sit waterlogged. Press compost back against the wall.
If the pot is no heavier after watering, the water did not stay in it. A container that has dried right out usually takes two or three waterings with the mix, then plain water until it next dries hard. Peat-based compost becomes very hard to rewet once it has dried right out; peat-free mixes go dusty and do the same. Take hanging baskets down and stand them in a trug. For a dusty 50 litre bag, start with 5 litres of mix — 25 ml from the bottle at 5 ml per litre — stir it through and leave it half an hour. Add more if a squeezed handful is still powder.
| Container | Starting water | From the bottle, at 5 ml per litre |
|---|---|---|
| 1 L pot | 100 ml | 0.5 ml |
| 10 L pot | 1 L | 5 ml |
| 12-inch hanging basket | 1 L | 5 ml |
| 30 L planter | 3 L | 15 ml |
Those water volumes are a starting point, about a tenth of the pot size, not a laboratory measurement. A badly dried pot will take more.
Calculate a pot doseOutdoor soil
Beds, borders and raised beds
Use it on beds, borders and raised beds when water beads or runs to the path. Scratch the top centimetre, apply slowly with the rose on, then water in with about another litre of plain water per square metre. A dry spell is one of those times: the water soaks in more evenly and can go deeper, so the root zone stays wet longer than if that water ran away. It does not store extra water the way compost does. Start at 2.5 ml per litre. A 3 m × 1 m border is 3 m²: 7.5 ml from the bottle in 3 litres of water at that rate, or 15 ml if you are at 5 ml per litre because the water still beads.
It will not feed the plants, fix compacted clay, or replace watering. Clay that ponds after rain is usually compaction: it needs a fork, not a surfactant.
Calculate a bed doseLeaves
Foliar nutrients and biostimulants
Add a wetting agent to a foliar nutrient or biostimulant spray so the spray spreads, stays on the leaf, and can be taken in. Seaweed, fulvic acid, and other feeds often bead up on a waxy leaf and roll off. Spreading the spray into a film is how more of it stays in contact with the leaf. Nobody has published a trial that measures a higher nutrient dose inside the leaf from this bottle.
01
Mix the water first
Put the wetting agent into the water and stir, then add the nutrient or biostimulant. Start at 5 ml per litre. Use up to 10 ml per litre if the spray still beads.
02
Wet both sides
A fine mist, until the leaves look wet, including the undersides, so the spray has more leaf to sit on.
03
Cool part of the day
Early morning or evening, not strong midday sun. A wet leaf in full sun can scorch. Keep the spray off open flowers while bees are working.
Use it in every foliar spray for as long as you are spraying. There is nothing to build up between applications. A 5 litre sprayer at 5 ml per litre takes 25 ml from the bottle.
Calculate a leaf sprayQuestions
Wetting agents, answered plainly
What does a wetting agent actually do?
It is a surfactant — a soap-like helper for water. It lowers the “skin” on a water droplet (surface tension) so the water spreads and soaks in rather than beading. That is the job on a lawn, in a pot, or on a bed. A dry spell is one time to use it, when water would otherwise run off. It does not store extra water the way compost does, and it does not feed the plant.
What do ml, L and m² mean?
ml is millilitres. 5 ml is one level teaspoon. L is litres. m² is square metres. A 3 metre by 1 metre border is 3 m². “5 ml per litre” means 5 ml from the bottle in every litre of water.
How much do I use per litre?
Soil, borders and pots: start at 2.5 ml per litre and use up to 5 ml if water still beads. Lawn: 5 ml per litre, and 1 litre of that mix per square metre. Leaf spray, with a foliar nutrient or biostimulant: 5–10 ml per litre, in the morning or evening. Planting: 2.5 ml per litre, once. A 9 litre can takes 45 ml at 5 ml per litre and covers 9 m².
Can I add it to a foliar feed?
Yes. Mix it into the water before the feed or biostimulant. It helps the spray spread and stay on the leaf, which is how more of a leaf feed can be taken in. Start at 5 ml per litre. There is no published trial that measures a higher nutrient dose inside the leaf from this bottle.
Can I use it on a lawn or bed in a drought?
Yes. Use it on lawns and outdoor beds while the ground is dry. Water that would bead or run off soaks in more evenly and can go deeper, so the root zone stays wet longer than if that water ran away. It does not store extra water the way compost does, it is not a feed, and it does not fix compacted clay. You still water again when the soil dries.
Can I use washing-up liquid or baby shampoo?
No. Both make water wetter, so both will wet a surface, but neither is made for soil. You cannot dose them, and they carry fragrance, dyes or salts chosen for a sink or for hair. Use the rate on this bottle.
Is a “natural” wetting agent as strong as a synthetic one?
They work the same way: they make water spread. A soap-nut extract is the milder one. In laboratory measurements, pure water sits at about 72 units of surface tension, soap-nut extract at about 52, and a strong synthetic at about 32–37. Nobody has published a head-to-head trial of this bottle on a UK lawn, border or pot. “Natural” on the label describes where the ingredients come from, not a performance score.
Evidence
Where these rates come from
The mixing rates in this guide are Dr Forest’s own for Natural Wetting Agent. The lawn papers used other, synthetic products on golf and sports turf. They are evidence for what wetting agents as a group can do, not a field trial of this bottle on a UK lawn, border or peat-free pot.
- Dr Forest Natural Wetting Agent — rates on the bottle, pack sizes and mixing order.
- RHS: lawns, dry patch — bone-dry soil that does not recover after rain. Spike, water a little each day, consider a wetting agent, and repeat monthly for 3–4 months with scarifying and aeration. The RHS does not set a dose.
- RHS: how to water containers — water the compost, not the leaves. A tray can catch runoff; empty it after a few hours so the pot does not stay saturated.
- Dekker et al. (2019), Geoderma — six applications of a synthetic wetting agent on a water-repellent Dutch golf fairway improved wetting and grass cover.
- Dempsey, Fidanza and Kostka (2025), Grasses — five wet years on golf turf in Ireland and Pennsylvania: the grass looked better, with no consistent rise in soil moisture. Those were wet seasons and a synthetic product, not a drought trial of this bottle, and not evidence that a wetting agent holds a bigger store of water.
- Powlen and Bigelow (2025) — on a sand golf green, watering a surfactant in immediately with about 5 mm beat waiting 18 hours, in late summer. Not a change to this bottle’s 1 litre per square metre.
- Aamlid, Espevig and Kvalbein (2009), Biologia — on a badly repellent golf green, turf quality improved 10–12 days after the first surfactant application. The soil under the thatch stayed repellent, so repeat treatment is the norm. A different product.
- Durand et al. (2021), Agronomy — peat-based compost becomes very hard to rewet once it has dried hard. A reason dried pots shed water.
- Rai et al. (2021), Sci — plant saponins (the soap-like compounds in soap nuts) lower the surface tension of water. Chemistry, not a garden trial.
- Wojtoń et al. (2021) — soap-nut extract lowered water’s surface tension from about 72 to about 52. Stronger synthetic surfactants go lower still. Laboratory work, not a lawn trial.
- Nemati and Jeong (2017), Acta Horticulturae — three commercial wetting agents on peat compost harmed plants at three to ten times their own recommended dose. Start at the low end of this bottle’s range.
How far a bottle goes
Coverage
How far each pack size goes
Bars are drawn to true scale, at the 5 ml per litre drench rate. The 5 litre covers ten times the area of the 500 ml.
| Pack | Makes | Covers | Cost per m² |
|---|---|---|---|
| 500 ml | 100 L | 100 m² | 14p |
| 1 litre | 200 L | 200 m² | 11p |
| 5 litre | 1,000 L | 1,000 m² | 8p |
Coverage at the top of the soil drench range, 5 ml per litre, applied at 1 litre per m².
A 3 m by 1 m border is 3 m², so at 5 ml per litre that is 15 ml of concentrate in three litres of water. A pair of 2.4 m by 1.2 m raised beds comes to roughly 6 m². A 500 ml bottle covers either of those many times over, which is why most gardeners treating specific problem areas rather than whole plots find the smallest size lasts a season or more.
Applying it so it actually reaches the roots
- Break the surface first. On badly repellent ground, scratch the top centimetre with a hand fork or spike it. A surfactant cannot get past a crust it never penetrates.
- Apply slowly. Poured on fast, the solution runs off exactly as plain water does. A watering can with the rose on, moving steadily, beats a hose.
- Water in with plain water afterwards. The surfactant needs to move down into the rootzone. Left on the surface it does nothing.
- Repeat. One application rarely settles established repellency. Monthly through the growing season is a reasonable working pattern.
When to apply it
Late spring, as soil warms and while there is still moisture in the profile, is the easiest time to re-wet ground. Repellent soil that has baked through July is the hardest case there is, and the reason a lot of people conclude these products do not work is that they first try one on ground that is beyond reach of a single watering can.
Timing
When to apply it through the year
Water-repellent ground is easiest to re-wet whilst there is still moisture in it. The window opens well before the patches show.
Best time to start
Repeat monthly through the season
Hardest ground to re-wet
Scarify to reduce thatch
If you are treating a bed that dried out badly last summer, treat it in April, not next August.
What a soil wetting agent will not do
It does not feed
There is no nitrogen, phosphorus or potassium in it. If the plants are hungry as well as dry, that is a separate job.
It does not store water
It changes how water distributes, not how much the soil holds. Water-retaining gels and organic matter do the storage job.
It does not fix compaction
Water sitting on compacted clay is a structure problem. Aeration and organic matter address it; a surfactant will not.
It does not replace watering
The point is that the water you already apply gets to the roots. You still have to apply it.
The published field trials on soil surfactants have been done almost entirely on managed turf rather than garden beds. Dekker and colleagues applied a surfactant six times to a water-repellent Dutch fairway and reported markedly improved soil wetting and turf performance. A five-year study by Dempsey, Fidanza and Kostka across sites in the USA and Ireland found consistently better turf quality and NDVI on treated plots, but no consistent difference in volumetric water content, which supports the distribution argument rather than a storage one. Soap nut saponins are naturally occurring surfactants, and Rai and colleagues review their surfactant properties. I have not seen a controlled garden-border trial of any wetting agent, natural or synthetic, and I would not want to imply otherwise.
Made in Stockport
Natural Wetting Agent
Six ingredients, including organic soap nuts and aloe vera grown in Stockport. 500 ml covers 100 m² at the 5 ml per litre soil drench rate. Handcrafted in small batches, in 500 ml, 1 litre and 5 litre.
Shop the wetting agentTreating a lawn instead? See the lawn wetting agent guide.
Frequently asked questions
When should I apply a soil wetting agent?
Late spring, as the soil warms and while there is still some moisture in the profile, then repeat monthly through the growing season if the problem is established. Ground that has baked dry through midsummer is much harder to re-wet, so treating in April beats treating in August.
Will a wetting agent fix hydrophobic soil?
It will help water penetrate hydrophobic soil, which is the whole purpose of a surfactant. It is not usually a single-application fix. Repeat treatments through the season, combined with breaking the surface crust and adding organic matter, do more than any one dose. On soil that is not actually hydrophobic it will make no measurable difference.
How much soil wetting agent do I need for my garden?
Work in square metres. The rate is 2.5 to 5 ml (0.5 to 1 teaspoon) of concentrate per litre of water, applied at 1 litre per square metre. At the top of that range, 5 ml per litre, a 500 ml bottle covers 100 square metres. A 3 m by 1 m border needs 15 ml. A 9 litre watering can takes 45 ml and covers 9 square metres. Most gardeners treating problem areas rather than whole plots find 500 ml lasts a season.
More wetting agent questions
Sources
- Dekker, L.W., Ritsema, C.J., Oostindie, K., Wesseling, J.G. & Geissen, V. (2019). Effects of a soil surfactant on grass performance and soil wetting of a fairway prone to water repellency. Geoderma, 338, 481–492. doi:10.1016/j.geoderma.2018.09.016
- Dempsey, J., Fidanza, M. & Kostka, S. (2025). Observations with soil surfactant applications to amenity turfgrass during higher-than-normal precipitation conditions. Grasses, 4(4), 42. doi:10.3390/grasses4040042
- Rai, S., Acharya-Siwakoti, E., Kafle, A., Devkota, H.P. & Bhattarai, A. (2021). Plant-derived saponins: a review of their surfactant properties and applications. Sci, 3(4), 44. doi:10.3390/sci3040044
Application rates are our own for this product. The cited studies used synthetic surfactants on managed turf and are given as evidence for the category, not for this formulation.
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