Wetting agents contain “amphiphilic” molecules with a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail. These molecules create bridges with the organic coatings surrounding the hydrophobic soil and reduce hydrophobicity.
Methylcellulose, acacia, pectin, surfactant–sodium lauryl sulfate, polysorbate 80, poloxamers, Pluronics, etc., are some of the wetting agents used in liquid formulations (Mahato and Narang, 2017).
You can make your own soil wetting agent using the food grade thickener, agar agar (algin), derived from seaweed. Buy powdered kelp from a health food store. Slowly add boiling water to agar agar and stir to make a paste about the same consistency as wallpaper paste.
If you ever run out of wetting agent, a good alternative is a few drops of washing up liquid - does same job.
Another way of making your own wetting agent is to add 3 drops of detergent to 5 litres of water. Make sure that you are using a plant-based detergent that does not have a fragrance as fragrances are often toxic.
Wetting agents are like a detergent or surfactant that attract water to the soils surface, helping it to soak in. Hydrophobic soils repel water which can lead to serious problems in the garden and lawn. For existing lawns that are hydrophobic, a wetting agent is needed.
Agar Soil Wetter Recipe
Here's a recipe to make your own natural Agar soil wetter at home: Mix agar powder/powdered kelp (available at health food stores) and 500ml boiling water until you get the consistency of thick custard. Add this mixture to a 9-litre watering can and fill it with water to dilute it.
In most domestic homeowner situations, the easiest and most accessible surfactant to use is dishwashing liquid. As mentioned earlier, soap contains the surfactant Sodium stearate. Liquid dishwashing liquid can be added to a tank mix of the herbicide or pesticide being applied and mixed with water.
The active ingredient is usually a 'surfactant', which behaves in the same way as a detergent: a long molecule that contains a 'tail' and a hydrophilic 'head'. The head can be positively charged (cationic), negatively charged (anionic) or carry no charge (non-ionic).
It may be a case that your soil has become hydrophobic or water repellent. This means that the soil or potting mix is unable to absorb any moisture and therefore, plants are not getting the water or nutrients they need. Hydrophobic or water repellent soil can also lead to water pooling and beading on the surface.
For bagged soil, seal your bags well after use to keep the soil from getting dry. You can even add a little extra water to the mix and blend it by hand before sealing it. The ambient heat should help re-wet the mix.
Application and Safety
Unlike fertilisers that can cause toxicity if applied too frequently or in too large an amount, wetting agents present no such risk. While they won't cause in problems, applying them too frequently is a waste of money – once they have done their job there is nothing more that can be achieved.
Polyacrylamides. These are synthetic surfactants that are very effective at reducing the surface tension of water. They are also relatively inexpensive, which makes them a popular choice for commercial potting mixes. The most common polyacrylamide in potting mixes is specifically anionic polyacrylamide (APAM).
While it is well known that both low-surface-tension and water miscible liquids, such as alcohols, and amphiphilic molecules, such as surfactants, are effective wetting agents, the detailed mechanisms for these agents to induce pore wetting remain unclear.
Adding dish detergent to your weed killer could tear apart the molecular structure of the chemical, making it less effective in killing weeds.
"Soap is a surfactant. Shampoo contains surfactant and detergents contain surfactants. Baking soda does not."
Hard-packed clay soils and even garden soils can become crusted and resist wetting, letting water run off instead of absorbing it. To re-wet, repeatedly sprinkle the surface lightly, making sure there is no run off. Covering the surface with a mulch such as straw, leaves, wood chips, or compost will also help.
Baking soda, in combination with soap and water, can help eliminate small weeds. Cover and protect lawn grass, ornamentals, and edible plants when using it in a spray. Apply weekly to prevent weeds from growing back.
A: Baby shampoo helps loosen compacted soil and improves water absorption without harming grass. Q: How do you apply baby shampoo to a lawn? A: Mix 1 tablespoon of baby shampoo per gallon of water, apply it using a sprayer, and water the lawn afterward.
All wetting agents are surfactants, but not all surfactants are wetting agents. Wetting agents are a class of surfactants that lower the interfacial tension of a liquid. An example is water. Water has a high interfacial tension, so a drop of water tends to “bead” on a hydrophobic surface, such as plastic.