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6 Brilliant Uses for Castile Soap in the Garden

Vegetables next to a bottle of Castile soap.

We’ve already discussed the many ways that Castile soap can save you time and money inside your home. So, how about you grab your favorite bottle of liquid Castile soap and head out to the garden.

I’m sure it’s no surprise that this soapy wonder has some great outdoor uses too. It might not be a bad idea to keep a bottle in your garden shed or garden box. (You do have a garden box, don’t you?)

But before we jump in, it helps to understand what makes this simple soap so useful.

Traditionally, castile soap was made from olive oil produced in the Castile region of Spain, hence the name. However, now it can be made with many natural oils – coconut, almond, avocado and hemp among them. (All of which are great for your skin.)

Instead of saponified fats that can strip away moisture, castile soap uses hydrating oils, meaning it cuts through the crud but isn’t drying like most soaps. This means it’s a-okay to use on your plants. (It’s the only soap I use on my wooden cutting boards and kitchen utensils.)

Grab your bottle of Castile soap (there are so many different scents to choose from), and let’s head outdoors.

1. Insecticide Spray

Hand sprays eggplant with homemade insecticidal soap

Bugs are everywhere, although, unfortunately, not as many as there used to be. This means more and more gardeners are careful about what they spray in their gardens. The decline of our pollinators has us reaching for things like neem oil when pests become a problem.

Castile soap is also an excellent, natural option for pest control in the garden. It works great on soft-bodied pests like aphids but does a good job on other bugs, too, like flea beetles, squash bugs and Colorado potato beetles. You can even use it to drown Japanese beetles.

Eggplant leaf with flea beetles on it.

In her advice on dealing with aphids, Lindsay advises us to use a homemade insecticidal soap made with, you guessed it, Castile soap.

Homemade Insecticidal Soap

  • You will need:
  • Quart jar with lid
  • Castile Soap
  • Water (if you have hard water, consider using distilled)
  • Measuring Spoons
  • Funnel
  • Spray Bottle

To Make:

Mix one tablespoon of Castile soap with 2 quarts of water in a jar. Screw on the lid and shake gently to mix. Using the funnel, transfer the insecticidal soap to the spray bottle. Don’t forget to label your bottle.

Remember, when you choose to use a spray, even a natural one, you’re affecting all the bugs in your garden, not just the pests. Always spray in the evening once the flowers have closed to reduce your impact on bees.

2. Powdery Mildew

Ingredients for powdery mildew spray.

Powdery mildew is a pain in the butt. There, I said it. Because the spores are carried on the wind and can overwinter in the soil, eradicating them is pretty much impossible. So, we’re left to deal with it every year.

But you can get ahead of it and keep it to a minimum by practicing good garden hygiene. Keep large susceptible plants like zucchini pruned well and mix up a batch of powdery mildew spray.

You will need:

  • Quart jar with lid
  • Castile Soap
  • Baking Soda
  • Water (if you have hard water, consider using distilled)
  • Measuring Spoons
  • Funnel
  • Spray Bottle

To Make:

Mix one teaspoon of Castile soap and one teaspoon of baking soda with 2 quarts of water. Screw on the lid and shake gently to mix. Using the funnel, transfer the insecticidal soap to the spray bottle. Don’t forget to label your bottle.

Spray your plants well, covering the tops and undersides of leaves, especially squash plants and bee balm, which are highly susceptible to powdery mildew. Spray later in the afternoon/early evening once blossoms have closed. But make sure you still have time for the plant to dry off before the dew settles.  

3. Wash Your Veggies

Bowl with soapy water and kale.

While technically this isn’t a garden use, it’s garden-adjacent. If you want to get technical, you could wash your veggies in your garden before you bring them inside. Plus, it works really well.

Use Castile soap to wash your fruits and veggies. Granted, it’s not so much of an issue if you’re picking them from your garden. That is unless you’ve been spraying with neem oil.

Let me tell you; neem oil-covered kale does not taste good.

Not that I know from personal experience, I’m just guessing.

Full-strength Castile soap works amazingly well at getting wax off of fruits like apples and citrus too, which is important when making homemade limoncello.

4. Clean Pots Before Reusing Them Again

Bucket with soapy water and pots.

Yup, this is one of those houseplant and gardening chores we love to ignore. That is until we lose one of our favorite plants.

It’s important to thoroughly wash out pots and planters before we use them again for a new plant. Most plant diseases are harbored in the soil, and when you put that soil in a porous pot, you’re just asking for trouble.

Take the time to give those pots a good scrub with hot water and Castile soap. Rinse them thoroughly and let them dry in the sun before using. Your plants will thank you.

5. Clean Garden Tools Before Pruning & at the End of the Season

Bottle of Castile soap next to gardening hand tools

This tip goes hand in hand with number four. Often, when we’re pruning a plant, it’s to remove dead or diseased parts of the plant. And while it’s best to clean your pruning tools immediately after you’re done (to extend the life of the tool), rarely do we remember.

It’s much easier to get into the habit of cleaning your tools right before you start pruning. Grab that bottle of Castile soap and hot water and clean your loppers, hand pruners and scissors well.

And don’t forget, if you are pruning off diseased portions of a plant, you must clean your tools before moving on to other pruning jobs.

Give all of your tools a thorough scrubbing before closing up the garden shed for the year, so they will be ready to go next spring.

6. Keep Cute Critters from Munching Up Your Garden

Two bunnies in the grass.

Bunnies are cute, aren’t they? With their long ears and those fluffy little tails, it’s hard not to love these sweet little creatures. That is until you watch them sit calmly in the middle of your flower bed, demolishing an entire hosta leaf in under twenty seconds flat without barely twitching a whisker.

Suddenly, these little eating machines aren’t so cute anymore.

No worries, though. You’ve got this.

Grab your trusty bottle of Dr. Bronner’s Peppermint Castile soap and a bottle of powdered cayenne pepper. Use the insecticidal soap recipe from earlier in the article and add a quarter of a teaspoon of powdered cayenne pepper to the spray bottle.

Critter control spray ingredients next to a blooming nasturtium.

Now you’ve got the means to keep Mr. Cottontail from nibbling your flowers and vegetables. Spray down your flower beds well, ensuring you coat all bunny-height vegetation. However, if you decide to spray your vegetables with this spicy-minty mixture, please refer to tip #3.

Hand holding spray bottle above nasturtiums.

Between the household and garden uses, I think you’ll need a bigger bottle of Castile soap. Don’t you?

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Tracey Besemer

Hey there, my name is Tracey. I’m the editor-in-chief here at Rural Sprout.

Many of our readers already know me from our popular Sunday newsletters. (You are signed up for our newsletters, right?) Each Sunday, I send a friendly missive from my neck of the woods in Pennsylvania. It’s a bit like sitting on the front porch with a friend, discussing our gardens over a cup of tea.

Originally from upstate NY, I’m now an honorary Pennsylvanian, having lived here for the past 18 years.

I grew up spending weekends on my dad’s off-the-grid homestead, where I spent much of my childhood roaming the woods and getting my hands dirty.

I learned how to do things most little kids haven’t done in over a century.

Whether it was pressing apples in the fall for homemade cider, trudging through the early spring snows of upstate NY to tap trees for maple syrup, or canning everything that grew in the garden in the summer - there were always new adventures with each season.

As an adult, I continue to draw on the skills I learned as a kid. I love my Wi-Fi and knowing pizza is only a phone call away. And I’m okay with never revisiting the adventure that is using an outhouse in the middle of January.

These days, I tend to be almost a homesteader.

I take an eclectic approach to homesteading, utilizing modern convenience where I want and choosing the rustic ways of my childhood as they suit me.

I’m a firm believer in self-sufficiency, no matter where you live, and the power and pride that comes from doing something for yourself.

I’ve always had a garden, even when the only space available was the roof of my apartment building. I’ve been knitting since age seven, and I spin and dye my own wool as well. If you can ferment it, it’s probably in my pantry or on my kitchen counter. And I can’t go more than a few days without a trip into the woods looking for mushrooms, edible plants, or the sound of the wind in the trees.

You can follow my personal (crazy) homesteading adventures on Almost a Homesteader and Instagram as @aahomesteader.

Peace, love, and dirt under your nails,