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Made by Growers · Backed by Science
Natural wetting agent for plants, soil, compost and lawns
Organic Soap Nuts In-House Grown Aloe No Petroleum Surfactants Foliar & Root Drench Lawn, Compost & Pots Handcrafted in Stockport
A natural wetting agent for plants is a plant-derived surfactant that lowers the surface tension of water, so water soaks into dry soil and compost instead of running off, and a foliar spray spreads across a waxy leaf instead of beading up. The working ingredient is saponin from organic soap nuts (Sapindus mukorossi). Dr Forest blends it by hand in small batches in Stockport, Greater Manchester, with aloe vera grown on site.
One concentrate does both jobs: a soil wetting agent for peat-based compost, containers and dry patch on a lawn, and a spreader for foliar feeds such as seaweed or fulvic acid. Made with organic ingredients, no petroleum or silicone surfactants, in 500 ml, 1 litre and 5 litre bottles.
10.1–11.5%Saponins in the soap nut
2.5–5 ml/LSoil drench rate
1,000 m²Treated per 5 litre
0Petroleum surfactants
What a wetting agent is used for in the garden
- Rewetting dried-out compost — peat-based composts shed water once they have dried right out; a soil wetting agent lets it soak back in evenly
- Dry patch on lawns and grass — brown areas that stay crisp however much you water them, because the thatch is turning the water away before it reaches the roots
- Containers and hanging baskets — stops water running down the gap between compost and pot wall and straight out of the bottom
- Foliar sprays — seaweed, fulvic acid and liquid feeds spread across the leaf and stay in contact rather than beading off
Does your soil need one?
Put a drop of water on the surface. If it soaks in within a few seconds, a wetting agent will not do much. If it sits there as a bead for a minute or more, it will. A lawn that is brown because it is hungry wants feeding rather than wetting, and our organic lawn fertiliser is the better answer there. Our guides to what a soil wetting agent does and fixing dry patch on a lawn go through telling the two apart.
A wetting agent is not a water retainer
It lowers the surface tension of water so the ground will accept it. It does not hold water there afterwards, and it will not reduce how often you need to water. If a thin or sandy soil dries out too fast rather than refusing to wet, what helps is organic matter or a clay amendment such as montmorillonite clay. Products sold as doing both are usually a surfactant plus a polymer. This is the surfactant half, sold as what it is.
Why soap nut rather than a synthetic wetting agent?
Soap nut and aloe vera concentrate
- Plant-derived saponin surfactant, biodegradable
- Works in the ground and on the leaf: one bottle for pots, lawns and foliar sprays
- Six ingredients, every one of them listed
Synthetic lawn and soil wetting agents
- Petroleum-derived or silicone-based, often reaching a lower surface tension than a saponin
- Persistence in soil varies by chemistry; some degrade quickly, others do not
- Often blended with polymers, dyes or fragrance, and the full ingredient list is rarely stated
What is in it
- Organic soap nut extract (Sapindus mukorossi) — the surfactant. Everything the product does, it does because of the saponins in this
- Aloe vera — grown organically in-house, harvested fresh for each batch. Its polysaccharides add a little body
- Vegetable glycerine — a humectant that slows how fast a sprayed film dries on the leaf
- Citric acid — holds the pH down so the preservative below can work
- Potassium sorbate — a food-grade preservative. The reason an aloe concentrate keeps for twelve months rather than a fortnight
- Reverse osmosis water — the carrier, purified so the calcium and magnesium that blunt saponins are not in the bottle to begin with
No animal-derived inputs. Saponins are not inert. Used at the rates on this page they are a surfactant and nothing more, but natural is not the same as has no effect on anything.
Handcrafted in Stockport
Blended and bottled by hand in small batches at our workshop in Stockport, Greater Manchester. The aloe is grown on site; the soap nuts are imported, since the Sapindus tree does not grow in a British climate. If you have tried washing-up liquid or baby shampoo on a dry lawn, our post on homemade wetting agents explains why the results disappoint. Made by Growers. Backed by Science.
The Science
The science of saponins: how a soap nut wetting agent works in soil and on leaves
What soap nut saponin actually is
Sapindus mukorossi, the Indian soapberry or washnut, is a deciduous tree of the Himalayan foothills. Its fruit shell carries about 10.1–11.5% triterpenoid saponins by weight (Sochacki and Vogt, 2022, Plants). Each saponin molecule has a water-avoiding backbone with one or more water-loving sugar chains attached, so one end is at home in water and the other is not. That split is the whole of the mechanism.
Dissolved in water, saponins gather where water meets air and lower its surface tension. Pure water sits at about 72 mN/m. A soap nut extract brings that down to roughly 52 mN/m; a strong synthetic surfactant reaches 32 to 37 mN/m (Wojtoń et al., 2021; Rai et al., 2021). A saponin is the milder surfactant. More on the terminology in wetting agent, surfactant or adjuvant: the difference.
Surface tension: what the numbers mean
| Liquid | Surface tension | What it does on a waxy leaf |
|---|---|---|
| Pure water | about 72 mN/m | Beads up and rolls off |
| Water with soap nut extract | about 52 mN/m | Spreads into a film |
| Water with a strong synthetic surfactant | 32–37 mN/m | Spreads further still |
The gap between 72 and 52 is the one a gardener cares about: the difference between water that beads and water that wets. The extra drop a synthetic achieves matters in industrial spraying and less on a lawn or a pot. On the leaf, a spread film stays put longer than a bead and dries more slowly; the vegetable glycerine slows that drying further. The aloe adds a little viscosity, and we make no wetting or film-retention claim for it.
A wetting agent lets water in. It does not supply it, hold it, or feed anything.
Mechanisms of action
01
Why dry soil and compost stop taking water
Soil turns water-shedding when long-chained organic compounds build up on and between the particles (Doerr, Shakesby and Walsh, 2000, Earth-Science Reviews). Sandy soils are the most prone, since there is less particle surface to coat. Peat does the same once dry: below roughly 40% water by weight it becomes very hard to rewet, and the drier it gets the worse it is (Durand et al., 2021, Agronomy). Lowering the surface tension lets water wet those coated surfaces instead of running past them.
02
Water goes down rather than sideways
On water-shedding ground, water finds the cracks, runs along pot walls and leaves the middle of the root zone dry however long you stand there with the hose. Wetting agents restore uniform wetting and rewetting of peat-based growing media; the same trial found that overdosing at three to ten times the label rate harmed plants, which is why the lower end of the range is the place to start (Nemati and Jeong, 2017, Acta Horticulturae).
03
What to expect on a lawn, and how soon
On a severely water-shedding golf green, a surfactant applied weekly through June raised soil moisture in the top 20 cm and produced statistically significant improvements in turf quality 10 to 12 days after the first application, with deeper rooting to match. Below the thatch the soil stayed water-shedding, which is why repeat treatment rather than a single dose is the norm (Aamlid, Espevig and Kvalbein, 2009, Biologia).
04
Why hard water blunts it
Saponins start working at a lower dose in soft water than in hard. In one measurement the concentration needed rose from 0.32 g/L in deionised water to 2.4 g/L in tap water, and the review literature agrees that hardness pushes that threshold up (Wojtoń et al., 2021; Sochacki and Vogt, 2022). Hence reverse osmosis water in the bottle, and rainwater or filtered water for diluting where you can.
05
What else a saponin does
Saponins lower surface tension and also interact with cell membranes; the two properties have been studied together (Böttger, Hofmann and Melzig, 2012, Bioorganic and Medicinal Chemistry). At the dilutions on this page the product is a surfactant and nothing else, but we would rather you knew the molecule has a wider life than pretend a plant extract does nothing at all.
Scientific references
- Sochacki, M. and Vogt, O. (2022). Triterpenoid saponins from washnut (Sapindus mukorossi Gaertn.): a source of natural surfactants and other active components. Plants, 11(18), 2355. doi:10.3390/plants11182355
- Wojtoń, P., Szaniawska, M., Hołysz, L., Miller, R. and Szcześ, A. (2021). Surface activity of natural surfactants extracted from Sapindus mukorossi and Sapindus trifoliatus soapnuts. Colloids and Interfaces, 5(1), 7. doi:10.3390/colloids5010007
- Rai, S., Acharya-Siwakoti, E., Kafle, A., Devkota, H.P. and Bhattarai, A. (2021). Plant-derived saponins: a review of their surfactant properties and applications. Sci, 3(4), 44. doi:10.3390/sci3040044
- Doerr, S.H., Shakesby, R.A. and Walsh, R.P.D. (2000). Soil water repellency: its causes, characteristics and hydro-geomorphological significance. Earth-Science Reviews, 51(1–4), 33–65. doi:10.1016/S0012-8252(00)00011-8
- Durand, S., Jackson, B.E., Fonteno, W.C. and Michel, J.-C. (2021). The use of wood fiber for reducing risks of hydrophobicity in peat-based substrates. Agronomy, 11(5), 907. doi:10.3390/agronomy11050907
- Nemati, M.R. and Jeong, K.Y. (2017). Wetting agent effects on plant growth. Acta Horticulturae, 1168, 63–70. doi:10.17660/ActaHortic.2017.1168.9
- Aamlid, T.S., Espevig, T. and Kvalbein, A. (2009). The potential of a surfactant to restore turfgrass quality on a severely water-repellent golf green. Biologia, 64(3), 620–623. doi:10.2478/s11756-009-0071-1
- Böttger, S., Hofmann, K. and Melzig, M.F. (2012). Saponins can perturb biologic membranes and reduce the surface tension of aqueous solutions: a correlation? Bioorganic and Medicinal Chemistry, 20(9), 2822–2828. doi:10.1016/j.bmc.2012.03.032
How to Use
How to use natural wetting agent: dilution rates and application guide
Measuring
Rates below are given in teaspoons and in millilitres. One level teaspoon is 5 ml. A standard 9 litre watering can takes 45 ml, which is nine teaspoons, and covers 9 square metres at the lawn rate, and at the top of the soil drench range. For other areas, the wetting agent calculator does the sums.
Shake well before every use
This is a naturally derived concentrate containing saponins that settle over time. Shake or stir vigorously before measuring and diluting. Soft water (rainwater, filtered, or dechlorinated) gives best results. Hard water can reduce saponin effectiveness.
Application rates
Foliar spray, helps a foliar feed spread across waxy leaves
Add to any foliar spray to improve leaf coverage and absorption. Mix with seaweed, fulvic acid, or foliar fertilisers. Apply as a fine mist to both upper and lower leaf surfaces. The saponins reduce surface tension, allowing the spray to spread and adhere rather than beading off.
When: early morning or late evening, never in strong midday sun. A spread film on a hot leaf in full sun dries too fast to be absorbed and can mark the foliage. How long for: use it in every foliar spray for as long as you are spraying. There is nothing to build up and nothing to rest between.
Root drench, dry soil and container rewetting
Apply to dry or water-shedding soil and growing media. Particularly effective for peat-based composts that turn water away once dried out. Water the solution across the surface and allow it to soak through. The reduced surface tension enables even moisture distribution throughout the root zone.
First, on a badly dried pot: if the compost has shrunk away from the sides, water once with plain water to settle it back against the walls, then apply the diluted solution. Otherwise the solution simply runs down the gap. How long for: a container that has dried right out usually takes two or three waterings with the solution before it wets evenly again. Once it does, go back to plain water and use the wetting agent again only when it next dries out hard. More on containers in why pots and baskets stop taking water.
Transplant drench
Water newly transplanted seedlings and plants with a dilute solution so that water makes immediate contact with the roots rather than running around the root ball. Particularly valuable when planting into dry soil, or when the root ball has dried out in transit.
When: at the time of planting, as the first watering in. How long for: once is enough. Water normally after that.
Lawn, grass and turf rewetting
Apply to lawns suffering from dry patch or a water-shedding thatch layer, the brown areas that stay crisp however much you water them. The reduced surface tension lets water move down through the thatch and into the root zone. Particularly useful after scarification or aeration, when the exposed soil surface can dry out and turn water away.
When: early morning or evening, on a cool or overcast day, never on turf in strong midday sun. Water the treated area in with plain water afterwards, roughly another litre per square metre, so the solution carries down into the thatch rather than sitting on it.
How long for: in the UK the useful window is roughly May to September, when the ground actually dries out enough to start shedding water. Applying in a wet spring achieves nothing. Established dry patch rarely clears on one application. The RHS cultural programme for dry patch is spiking and hollow-tine aeration with thorough watering, repeated once a month for three to four months. On wetting agents themselves the RHS says only that repeat treatment is likely to be necessary, in conjunction with those cultural methods. So read the monthly rhythm as the cultural programme the wetting agent accompanies: apply monthly through the dry spell alongside spiking and thorough watering, and keep watering normally in between. A wetting agent lets water in; it does not supply it.
Compost tea and biological brew additive
Add to compost teas, aerated brews, or microbial inoculants to improve application spread. Improves soil contact and distribution of biological inputs.
When: at the point of application rather than at the start of the brew, and apply the brew the same day.
Step-by-step preparation
- Shake the bottle vigorously. Natural saponins settle between uses. A good shake ensures consistent concentration in every measure.
- Measure the required amount. One level teaspoon is 5 ml. Start with the lower end of the recommended range and increase if needed.
- Add to your water or spray solution. Stir or agitate to distribute evenly. If adding to a foliar feed, mix the wetting agent into the water first before adding other inputs.
- Apply promptly. For foliar sprays, use a fine mist setting and target both leaf surfaces. For soil and lawn drenches, water evenly across the area. Apply in early morning or late evening to maximise uptake and minimise evaporation.
- Water in, on lawns and bare soil. Follow a turf or soil application with plain water so the solution travels down into the thatch and root zone rather than drying on the surface.
How to tell whether it has worked
Judge it on water, not on colour. The morning after treating, put the hose or can on the treated ground and watch what the water does. If it now sinks in where it previously beaded and ran to the edges, the wetting agent has done its job. Green-up is a separate and slower thing: it follows over the following week or two, and only where the grass crowns are still alive. Where the grass has actually died off, the patch will need reseeding once the ground is accepting water again.
Soft water works best
Hard water contains calcium and magnesium ions that can interact with saponins and reduce their surfactant effectiveness. For best results, use rainwater, filtered water, or water that has been left to stand and dechlorinate. If only hard tap water is available, the product will still work. You may just need the higher end of the dilution range.
Works well combined with…
Use alongside Organic Seaweed Extract Powder for foliar sprays where leaf coverage matters, with Fulvic Acid Powder for chelated foliar feeding, and with any Dr Forest crop-specific fertiliser applied as a liquid feed. On a lawn, pair it with Organic Lawn Fertiliser: the wetting agent gets the water in, the feed does the growing.
Storage
Keep cool, dark and tightly capped. The concentrate keeps for at least 12 months from opening. Use diluted solution within 24 hours; the dilute solution is not preserved. Shake before each use.
Questions & Answers
Frequently asked questions about natural wetting agent
A wetting agent is a surfactant, which means it lowers the surface tension of water. Pure water has a surface tension of roughly 72 millinewtons per metre, which is why it beads up on waxy leaves and on dry, water-shedding soil instead of spreading. Lowering that surface tension lets the water spread and soak in rather than running off. It does not feed the plant and it does not hold water in the soil.
For a soil drench, 0.5 to 1 teaspoon, which is 2.5 to 5 ml, per litre of water, applied at one litre of solution per square metre. For a lawn drench, one level teaspoon, which is five millilitres, per litre, at the same one litre per square metre. For a foliar spray, one to two teaspoons, which is five to ten millilitres, per litre. A 9 litre watering can takes 45 ml and covers 9 square metres at the top of the soil drench range, 5 ml per litre.
At 5 ml per litre and one litre per square metre, the 500 ml bottle makes 100 litres and treats 100 square metres, the 1 litre treats 200 square metres, and the 5 litre treats 1,000 square metres, which is the size most people want for a full lawn or an allotment. Those are top-of-range figures; at the lower end a bottle goes further.
Yes, and it is the most common use. Dilute at 0.5 to 1 teaspoon per litre and water it across the surface. If the compost has shrunk away from the pot wall, water once with plain water first so the solution soaks through rather than running down the gap. A pot that has dried right out usually takes two or three waterings with the solution before it wets evenly again.
The water behaves differently straight away: on the next watering, water that used to bead and run to the edges should sink in, and that is the thing to check first. Green-up follows over the next week or two as the root zone rewets, and only where the grass crowns are still alive. Dry patch left for a whole summer usually needs applying monthly through the dry spell, and grass that has actually died will need reseeding.
No. It gets water into ground that is refusing to accept it. It does not store water there and will not extend the gap between waterings. If your soil wets easily but dries out too fast, the answer is organic matter and the soil's own moisture-holding capacity rather than a wetting agent.
Six things: organic soap nut extract, aloe vera grown in-house in Stockport, vegetable glycerine, citric acid, potassium sorbate and reverse osmosis water. The soap nut extract carries the saponins, which do the work; the citric acid holds the pH down so the potassium sorbate, a food-grade preservative, can keep the concentrate stable for twelve months. It is made with organic ingredients and is plant-based, with no petroleum or silicone surfactants, no fragrance and no colourants.
Washing-up liquid is a surfactant too, so it will lower surface tension. It is not formulated for soil: the surfactant concentration is unstated, so you cannot dose it, and it carries fragrance and colourants that serve a sink rather than a garden. This is a soap nut concentrate made for the job, at a stated rate. The longer answer is in washing-up liquid as a wetting agent: why it fails.
It is a plant-derived soap nut concentrate with a food-grade preservative, and used at the label rates it is a surfactant and nothing more. As with any concentrate, keep the bottle out of reach of children and pets, and do not spray in strong sun or onto open flowers while bees are working them.
Stored cool, dark and tightly capped, the concentrate keeps for at least 12 months from opening. That is down to the potassium sorbate; fresh aloe on its own would not last a month. Use diluted solution within 24 hours, as it is not preserved. Every question we get asked is collected in the wetting agent FAQ.
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