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Insecticidal soap sprays in your garden: not all soaps are made equal

It’s that time of year when we are seeing the pests appear on plants in the garden, this year it has been aphids swarming the hellebore, black currants, hydrangea and aquilegia, but I know from experience, they will eventually find the greenhouse and the peppers and soft herbs will be a target. So I thought this might be the perfect time for me to talk you guys through some of the stuff I have learned about different homemade remedies, so you don’t have to try to sift through the mountain of info and opinion for yourself.

Now I’m a few years on now, since the first time I experienced this and my first absolute panic of not knowing what to do. That first year I turned to the only thing I knew and I went full-on Rambo with the bug spray. Since then though, I’ve been learning and I now know of some other methods which means I don’t have to worry about toxic chemicals, cause let’s be honest, a lot of our garden is actually food we, personally, eat so I’d rather avoid chemicals on it. However, this area isn’t as simple as it is made out to be online and even on TV gardening shows. So today, we are going to start with insecticidal soap. Because believe it or not, there are a lot of blog and youtube videos out there talking about this, but it’s still quite hard to work out what you should and shouldn’t use and how.

So jumping in 🙂

Plant health & safety

I want to remind you guys of some plant health and safety first. As always, remember what works for me might not work for you and you may even find what worked for you before doesn’t work now. There are some factors to go into about this, but for just now just think of it this way. Test a small patch of leaves on a plant and give it a couple of days to make sure the spray isn’t actually going to do any damage before you go mad and spray further. Remember, you can always dilute the recipe down if your plant leaves are damaged, but if you spray your whole garden and the recipe was too strong… it’s too late.

Some plants are also more easily damaged than others and the time of day you spray can have an effect too. Think about on a hot day, in the morning your plants are all lush, and the leaves look awesome, green and strong, then at lunchtime, the heat has got to them and they are a bit limp and feel more delicate. Well, this is what I mean about different times of the day and even different seasons will affect how your spray works. Quite simple, avoid spraying your plants when they are suffering, from heat or otherwise. If they are already feeling a bit under the weather, smothering them with soap isn’t going to help and they will be more susceptible to damage. So stick to cooler days, or early morning and late evening when it’s cooler. You’ll know your garden better than anyone so you’ll know when the right time is for your plants.

So first lets talk about aphids, because that’s what you are most likely trying to control.

Aphids are soft-bodied insects. They gather on the new growth, soft stems and inside new buds of your plants and they suck the sap out of the plant. Literally they suck the life out of the plant. The damage they do can go from patchy or mottled leaves, curled brittle leaves to the plant actually dying if you have a bad infestation. Aphids can also transfer fungus and disease from plant to plant too.

If you catch them early, you can kill them by simply squishing them. Just between your thumb and forefinger, just squish them off the plant. Or I’ve found blasting the plant with the jet of the hose works well too as if you can knock them off the plant they rarely survive long enough to climb back onto the plant. But sometimes the infestation gets really big before you catch it and in this circumstance, you may want to turn to a spray to deal with it. This is where the old remedy of soap spray (or insecticidal soap) comes in.

Soap, really?

Ok so this is where we get to the bit for which I’ve found the most varied and contradictory information out there. It’s also the bit that I’m not finding easy to explain, so this section may be long and waffly.

And here is where some of the problems occur today. For every video on YouTube telling you how great soap sprays are for the garden, there is another one with a story of how that same soap spray killed their plants and I think the simplest way to explain that is this.

Back in the times of old, There were no factory produced options so people had to make their own solutions to things, so many remedies were made from household or garden things. This also meant that you could be pretty sure that whatever remedy was, it was pretty much natural as this was really the only thing available. No chemical plants and mad scientists at your disposal. Today we have all of that, but for many reasons some of us want to go back to those household remedies. What we maybe don’t realise is that even if the recipe hasn’t changed, the ingredients have. And this brings me to soap. Yup… soap.

Right soap… sounds simple enough cause we all know what soap is, in fact, we all have lots of it around the house. Dish soap, hand soap, shower soap etc. But… actually almost all of them are not actually soap. I know right? So put it this way, when you hear, read, see folk talking about making these soap sprays, they are referring to pure soap. To make this clearer go grab your dish soap (washing up liquid if you are in the UK).

I’ve grabbed ours and looking at the label, it doesn’t even say the word soap on it, ANYWHERE. It does say dishwashing liquid. That’s because these days, most of the items we refer to as soap as actually no longer soap and instead detergents or solutions of chemicals which have replaced actual soap. The label does, however, say a lot.

Ingredients in my washing up liquid.

  • Aqua
  • Sodium laureth sulphate
  • Alcohol denat
  • Lauramine oxide
  • C9-11 pareth-8
  • Sodium chloride
  • 1,3-Cyclohexanedimethanamine
  • PPG (polypropylene glycols)
  • Dimethyl aminoethyl methecrylate/hydroxyproply acrylate copolymer cirate
  • Parfum
  • Geraniol
  • Limonene
  • Colourant

There is also a big exclamation warning label on there to let us know that is it harmful and a strong irritant and much more.

So let me explain the soap thing. Actual soap, as used by gardeners of other generations who were forced to make home remedies was a much purer item. Traditionally (what we now call simple or pure) soap is made by mixing sodium hydroxide, or potassium hydroxide with fats or oils. This creates something called sodium salt of fatty acid, or potassium salt of fatty acid. This is what you’ll find in most bars of soap. Chemically this is very different from dish soap or detergents.

Insecticidal soap is made using only potassium which creates much milder soap than sodium using long-chain fatty acids – a particular type of fat. This soap is specially made to be mild on plants. This is important to note because what we often see recommended when gardeners talk about soap sprays these days is actually dish soap or detergent. Now detergents are specifically created to be excellent at removing oil and grease, even wax. Unfortunately, natural oils and waxes are what you will find on most plant leaves. These are there as a protective coating on the leaves. When that protective coating is removed from the leaves, it makes it easier for pathogens to get a foothold and then infect the plants. As you can imagine, spraying even diluted detergents onto your plants risks actually removing their natural defences against pests and diseases.

So how traditional soap spray works as a pest control method is because the fats in the soap actually damage the cells on a soft-bodied insect, like aphids, killing them. So when you make a solution of soap and water and spray it onto the aphids on your plant you kill them. Hence why the tradition of soap sprays to kill bugs on your plants has lasted through the ages. It’s just unfortunate that we still have the knowledge of the remedy, but the ingredient has changed.

As you have seen, however, today’s soaps (and dish soaps/liquids) are no longer made with soap but instead, there are a lot of ingredients in there which make our lives easier but which can be harmful. This is true of your garden too. I do apologise to those of you who are now put off using these soap sprays because you were trying to avoid introducing unnecessary chemicals into your garden but there is a silver lining.

So firstly, you can actually still buy simple or pure soap if you’d prefer to make your spray to the proper and traditional recipe. To be honest, though, it’s not the easiest thing to get your hands on and it’s not as cheap as the dish soap you can buy from your local shop. However, you choose to still use detergents in your garden sprays be very aware of the concentration of this spray. You wouldn’t make this type of spray to the same recipe as those using traditional soaps. You will still see a degree of success from soap sprays using modern soaps as let’s be honest all those chemicals in there will kill the soft-bodied insects like aphids. However, you will need to think about the recipe you are using and be aware that you are potentially weakening/damaging the plant. So keep that in mind.

This is where my warning about testing a small patch first comes in. You will definitely want to keep an eye on the strength of the soap you are using and for instance, if you are using a concentrated liquid detergent then dilute the recipe down. See before mentioned comment about testing a small patch first. And also be aware of the warning labels on some of our dish soaps etc, especially if you have a pond or other water feature in your garden.

My recipe

So I use pure soap in my garden spray. Knowing what I do now I wouldn’t risk using dish soap in my garden. My recipe is this simple…

  • 1 litre of water, and,
  • two tablespoons of soap.

That’s it. Give it a shake to mix before you spray it and bob’s your uncle. This will kill most soft-bodied insects once you’ve sprayed them and is mild enough not to harm my plants. I wouldn’t use this recipe if I was using a modern dish soap though. Just always be sure to make a weaker version of any recipe to test on your garden first. You can then adjust as you see fit and by testing, you’ll find the solution that’s right for you without damaging your prized garden.

And that’s it. That simple. I have found that one spray (with my pure soap) can get infestations under control in 4 days. Happy camper.

Is a soap spray harmful to other garden life?

This is a question I’ve had asked lots and I’m sorry to say, yes, it can be. Even using the other traditional soaps, you are introducing something to the garden that isn’t naturally there. And as I’ve just explained modern soaps are no longer the purer version these remedies were created with and so please do be aware that the chemicals in the moderns soaps can be harmful to humans and other animals if misused. So when spraying in your garden, only spray the areas of the plant with the insects on. Avoid spraying randomly around plants and do not overdo it. Remember you may have other beneficial insect life on the plants and you will definitely have pollinators around. Avoid spraying flowers if you can and avoid areas where the birds feed, such as hedgerows, berries etc. And as I’ve already said, be careful of water features, ponds etc as animals will I’ve there or drink from them.

Now, this spray is particularly for controlling soft-bodied insects, you may also have other pests which chew on leaves or fruit (think back to my problem with earwigs eating my peppers). In this case, there is a different home remedy spray we can use, called neem oil. But that one will be the next blog post.

Check out the video above for much more details

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