A Guide To Making Homemade Insecticidal Soap For Plants

Insecticidal soap, also known as horticultural soap, is a non-toxic, environmentally friendly insect repellent to prevent infestations from pests such as aphids, whiteflies, spider mites, and mealybugs. 

Insecticidal soap contains active ingredients like potassium salts or soap salts of fatty acids, which are created by mixing the chemical compounds with the fatty acids found in castor, coconut, olive, whale, fish, or veggie oil.

The chemical concoction kills common garden pests and insects on contact. The soap does not leave toxic residue in the soil.

Commercial Soap

There are two different kinds of commercial insecticidal soap available: ready-to-use and concentrated solution

Ready-to-Use

There are tons of ready-to-use insecticidal soap in the market. It comes packaged in a spray bottle and is priced differently, depending on the brand. Many gardeners use commercial ones because of convenience.

It is already mixed in the correct proportions, so there is little chance of getting the recipe wrong. It may be labeled as suitable for organic use or safer for plants and vegetables.

However, instead of focusing on the labels, you should look at the ingredients if you are looking for a true insecticidal soap. The soap should contain either potassium salts of fatty acids or potassium laurate.

Concentrated Solution

Commercial insecticidal soap also comes in a concentrated solution. This solution is mixed with water according to instructions. It does not come with a pump sprayer, so you might need to buy one if you do not have it. 

It is better to invest in a separate pump sprayer and then purchase the solution after every use. A concentrated solution might cost more but will last longer than a ready-to-use spray.

Homemade Soap

A homemade insect repellent or soap is the cheapest option. The soap itself is the active component in insecticidal soap. Although many homemade recipes might suggest adding ingredients like garlic or cayenne, it is the soap that effectively eliminates the pests. 

Choose a fragrance-free soap without additives like bleach, as these can harm beneficial plants and insects. A more natural homemade insecticidal soap solution is less likely to affect desirable plants and bugs.

If you want to make insecticide soap at home, be sure to follow this insecticidal soap recipe carefully. Too much or too little of anything could ruin the ratio and the soap’s resulting effectiveness.

Ingredients:

• Liquid Castile soap (not dish soap)
• Warm water
• Optional: Vegetable oil

Equipment:

• Spray bottle
• Water jug/container

Instructions:

Select the Right Soap

There are many homemade insecticidal soap recipes online, and all start with choosing the right kind of soap. You can use any mild, fragrance-free soap, but castile soap is the best. 

Castile soap is made from plant-based oils without chemicals, dyes, or fragrances. This lack of chemicals makes it gentle on plants and eco-friendly.

Despite being gentle, it can kill off soft-bodied insects without affecting the beneficial insects. 

Add Water to the Jug

Fill a 1-gallon jug with either distilled or tap water, as long as it is not hard water, as it reduces the effectiveness of insecticidal soap. You can purchase the water from the grocery. It should not be mineral-enhanced water. 

You can also fill the solution in a garden sprayer.  Fill the spray container with water. You can use any amount of water if you use the correct ratio of water and soap. 

Add Soap and Oil

Add 2-½ tablespoons of castile liquid soap and 2-½ tablespoons of vegetable oil. You can use coconut, olive, or grape oil if you do not have regular vegetable oil.

Both the liquid soap and the oil serve as surfactants, helping the solution adhere to the leaves and preventing it from running off quickly when sprayed.

The longer the solution stays on the leaves, the more effective it is at killing the invading insects. However, do not increase the amount of soap or oil, as the solution must be mild to avoid harming the plants.

Mix the Ingredients

Cover the jug or spray bottle with a lid and shake the solution to mix the ingredients. Pour the mixed solution into smaller spray bottles.

Shake the solution container each time you refill a spray bottle to ensure the ingredients are evenly distributed and to avoid applying a solution that is too weak or too strong. 

Also, frequently shake the spray bottle while spraying to keep the solution well-mixed.

So, how does homemade insecticidal soap for plants work? A homemade insecticide works by killing soft-bodied insects that threaten the health of your plants. 

Ruptures Cell Membranes

When the soap comes in contact with the insects, the fatty acids in the soap embed themselves in the waxy, lipid-based outer layer of the insects and disrupt their protective function.

Once the soap molecules force their way into the insect's protective layer, they integrate with the cell membrane composed of lipids. This integration disrupts the structure of the cell membrane, causing it to rupture. The insects then die. 

Suffocation 

If the soap molecules cannot rupture the insect's cell membranes, it can contribute to their demise through suffocation. Insects have tiny openings called spiracles found along the thorax and abdomen. 

When insecticidal soap touches the spiracles, it can block them.  This blockage prevents oxygen from entering the insect's body and carbon dioxide from escaping.

As a result, the insect suffocates due to the disrupted gas exchange and eventually kills the insect. 

Contact Kill

Insecticidal soap is only effective when it comes in contact with the insect. 

Therefore, for maximum effectiveness, it is essential to ensure that the soap solution covers the entire insect. You might also need to repeatedly apply the solution to control a pest infestation effectively. 

There are many recipes online that recommend using dish soap in homemade insecticidal soap. This confuses people into thinking a true insecticidal soap is the same as one with dish soap.

However, one made with dish soap is different from an insecticidal soap.

What are Dish Soaps

Dish soaps are detergents, not soap, made of synthetically produced chemicals designed to cut through grease and oil from cookware.

They are more powerful and aggressive than regular soap because they contain more aggressive surfactants to break down stubborn food particles and grease.

They do not include moisturizing ingredients like glycerin to prevent skin dryness. They also tend to have a higher pH level, which can be drying to the skin. 

Dish Soap Effects 

The dish soap can affect plants and other beneficial insects.

Effect on Plants

Using insecticidal DIY soaps made from dish soaps may be harmful. It may be effective in killing insects. However, it may cause more harm than good.

The harsh chemicals in dish soap may remove the waxy layer from the surface of the plant’s foliage. This removal makes the plant vulnerable to microbial, viral, and fungal diseases. 

The loss of this waxy cuticle also causes the plant to lose more water, effectively drying the plant out. Plants with a thick waxy layer, like succulents, are more affected than others.

Effects on Beneficial Insects

Insecticidal soap is less aggressive and can break down the cell membranes or soft-bodies insects and kill them. It might not work on beneficial insects with tough exoskeletons, like ladybugs, lacewings, and predatory mites. 

However, dish soap contains harsh chemicals that kill these beneficial insects. So, even if they are an effective cleaning product in the kitchen, they should not be used in your homemade insecticidal spray. 

Although insecticidal soap is safe for most plants, you should not use it on certain plants as they are sensitive to its effects. Below are some plants that are not suitable for the soap. 

Delicate foliage plants

Delicate plants have thin, fragile leaves that are easily damaged. When the leaves come in contact with the soap, they absorb it. The chemicals in the soap will break down the cell membrane and structure of the leaves and lead to burns or discoloration. 

Some examples of delicate plants are ferns, African violets, peace lilies, heartleaf, Chinese evergreen, impatiens, coleus, begonias, and fuchsia. These plants are not equally sensitive. Some are more sensitive than others, so it is always wise to conduct a patch test. 

Wax-coated plants

Wax-coated plants have a protective, waxy layer on their leaves. This coating helps to conserve water, protect against pests, and sometimes even provides a bluish or silvery appearance. 

These plants are sensitive to insecticidal soap because the soap molecules bind to the wax. This binding breaks down the waxy layer into small droplets that can mix with water. The emulsified wax is washed off the plant's surface.

Without this coating, the plant is more vulnerable to water loss, pest infestations, sunburn, and environmental stressors. 

Flowering Plants

Insecticidal soap is generally safe, but it can harm flowers. Direct spraying on blossoms can damage them, causing spots, discoloration, and premature dropping. 

Additionally, some insecticidal soaps may repel pollinators like bees and butterflies, hindering fruit and seed production. 

Even if the soap is rinsed off, its residue could affect fruit development.

Once you have made the solution, you need to apply it. But before applying, here are some things you should know. 

Test on a Small Area

Before applying the solution to the entire plant, spray it on a small, inconspicuous area. Check the area the next day for any adverse reactions.

Some plants can be sensitive to soaps and other chemicals and might react negatively. The reactions could range from leaf burn to discoloration, which might not be apparent immediately. You can identify potential problems and avoid damage by testing a small area. 

Application Time

The solution should be applied early morning or late afternoon during cool hours to reduce the risk of leaf burn. 

There is little sunlight during these times, allowing the soap solution to stay on the plant leaves longer instead of evaporating quickly. 

Spray the Plants

When applying the solution, ensure you coat the plants thoroughly because it is a contact-kill solution.

So, remember to spray on both the tops and undersides of the leaves, as well as stems and buds where pests are present. If you miss a spot where the bugs are, they might multiply, rendering your solution useless. 

Avoid Direct Sunlight

Applying insecticidal soap in direct sunlight can increase the risk of burning or damaging the plants. 

This is because the water droplets from the insecticidal soap attract the heat from the sun's rays and cause plant tissues to overheat. Overheating leads leads to burned, brown, or discolored spots on the leaves.

Rinse (Optional)

If your plants are sensitive, apply the solution on infected parts and rinse it off a few hours later. Rinsing will reduce the risk of damage. 

Reapply as Needed

Applying the soap once is ineffective. You might need to reapply as necessary, usually every 5-7 days, until the pest problem is under control.

Reapplication is often necessary because new insects can hatch or arrive after the previous application. You might have missed some spots during the first application. Rain and watering can wash away the soap, reducing its effectiveness.

Protect Beneficial Insects

Although beneficial insects are usually unaffected by the soap, constant contact can damage their exoskeletons and kill them. 

So, when spraying the solution, look out for these insects and avoid spraying them directly. Apply the soap only where pests are present.

Monitor Your Plants

Regularly checking plants after using insecticidal soap is crucial. This regular check-up helps you see if the soap is effective against pests and lets you spot any harm it might be causing to the plants, like burnt, wilted, or discolored leaves.

It tells you if a reapplication is needed or if the initial treatment was sufficient.