Bug infestations are a gardener’s worst nightmare. While there are a wide range of insecticides available. for those of us who are trying to garden organically, or just use as few potentially harmful products as possible, it can be difficult to find an effective and affordable insecticide. Luckily, the answer may already be in growing your garden: rhubarb leaves.
Rhubarb is a plant of contradictions. While its long, juicy red stalks can be used to make tarts, crumbles or preserves (amongst other things), rhubarb leaves are poisonous. This means that they can be used to combat unwelcome garden pests such as aphids. Gardeners have for this reason, traditionally used rhubarb leaves as a natural, chemical free insecticide.
Reasons to be Careful
As with all insecticides there are some dangers associated with using a rhubarb leaf insecticide. Before we look at how to safely make and apply this insecticide I am going to take a few paragraphs to highlight the possible dangers and explain how they can be avoided.
Rhubarb leaves contain a high concentration of oxalic acid. This means that rhubarb leaves are toxic.
The toxin present in rhubarb leaves is at its most effective when drunk. That said, if enough is ingested in any form, it can lead to nausea, illness, and in the most extreme cases, death. While this is bad news for any humans who accidentally consume rhubarb leaves, this potent toxicity is what makes rhubarb leaves a great organic insecticide.
Many people who have cats or dogs avoid using insecticides made from rhubarb leaves. This is because dogs in particular can be drawn to the soap in the insecticide mixture and may lick the leaves of the plant, accidentally ingesting the toxins. In the worst cases this exposure could lead to the pet becoming seriously ill or dying.
While the chances of this happening are slim, many people choose not to take the risk. If this applies to you then there are plenty of other affordable, chemical-free insecticide options available.
My personal favorite is one that isn’t only easy to make, but is also safe to use around pets. Simply apply a warm soapy water solution to the leaves of the afflicted plant. This is a long-standing method of getting rid of garden irritants such as aphids.
Hazards to Take Note Of:
It’s also advisable not to spray insecticides made from rhubarb leaves onto any edible plants, vegetables, or flowering fruit like tomatoes. As we’ve already mentioned, rhubarb leaves contain oxalic acid which, if consumed in a large enough dose, can be deadly.
While for many people inadvertently consuming a small amount of oxalic acid won’t have any noticeable effect, for some people even a small amount can lead to illness or nausea.
If a small amount of rhubarb leaf insecticide is applied by accident to an edible plant, don’t worry: the plant isn’t completely lost. Remove as many of the afflicted leaves as possible without harming the rest of the plant.
Wait Before Harvesting
You should then wait at least a couple of weeks before harvesting the crop. This is because the toxins present in the rhubarb leaves break down relatively quickly. As such, there should be little to no trace of them after a few weeks.
Wash the produce thoroughly after harvesting. It should now be safe to consume. If you’re still concerned, know that cooking methods such as blanching reduce the risk of oxalic acid poisoning even further.
Obviously, if a larger amount of the insecticide is accidentally applied to an edible plant, or you’re truly concerned, then the wisest and safest thing to do is to dispose of the crop.
Unlike more sophisticated pest control methods, insecticides made from rhubarb leaves don’t discriminate between good visitors—such as pollinators—and unwelcome visitors like aphids. Careful application at the right time of day (which we’ll discuss later in the article) helps to minimize the risks.
Making an effective insecticide from rhubarb leaves is a straightforward process. Here’s how you do it:
What You’ll Need:
- An old pot or saucepanthat you won’t use for food preparation again
- An old stirring spoon that you won’t use for food preparation again
- A chopping board or surface that you can wipe clean afterwards
- A sharp knife
- Timer, watch or clock
- Funnel (optional)
- A strainer, sieve, or cheesecloth
- A clean bucket
- Dishwashing detergent or soap flakes*
- A clean spray bottle
- Measuring cup.
- If you plan on making a large amount of rhubarb leaf insecticide, you’ll also need a secure storage jar or bottle with a cap
*IMPORTANT: Do not use laundry detergent or any other harsh detergents. Avoid anything that comes with a long list of chemicals on the label. Those chemicals won’t just harm your plant: they’ll also contaminate the soil and harm surrounding plants. If you’re unsure of what to use, choose a garden or biodegradable soap. These work just fine without any danger of further harming your plants.
Step 1: Collect Some Rhubarb Leaves.
Head to a supermarket or a fruit and vegetable market and buy some rhubarb that still has its leaves attached. Or, if it grows in your own hard, harvest an armful of it.
However you acquire your rhubarb, make sure that it’s organic. Don’t risk harming your garden by using rhubarb leaves that have had unknown chemicals sprayed onto them.
The amount of rhubarb leaves you’ll need depends on the amount of insecticide you want to make. Just be warned: this insecticide loses its potency quickly if not stored correctly. (I’ll explain how to do this later in the article.)
Step 2: Preparation.
Remove the rhubarb leaves from their stems. The stems can then be used in a variety of ways, the tastiest of which, in my opinion, is a rhubarb crumble.
Chop the rhubarb leaves roughly so that the following steps are easier.
If you’re concerned about the toxins present in the rhubarb leaves, or have sensitive skin, wear either rubber gloves or a sturdy pair of gardening gloves when doing this. Make sure to thoroughly wipe down the chopping board or work surface after you’ve finished.
Step 3: Creating a Rhubarb Infusion.
Now that you’ve chopped the leaves, it’s time to make the insecticide.
Add water to an old pot or saucepan. The amount of water you need depends on the amount of rhubarb leaves you intend to use. Use three cups of water for every cup of rhubarb leaves.
Bring the water to the boil.
Once the water is boiling, add the leaves and stir them in. Reduce the heat and allow this mixture to simmer for 30 minutes. If you’re using a large amount of rhubarb leaves, allow the mixture to simmer for slightly longer.
Keep an eye on the mixture and stir it occasionally. If it looks like the liquid is evaporating, reduce the heat slightly and add a little more water.
Once the 30 minutes are up, remove the pot from the heat and allow the mixture to cool completely.
Step 4: Straining the Rhubarb Leaves.
Once the mixture has cooled completely, it’s time to tackle the trickiest step in the process.
Firstly, skim away any sediment that has formed on top.
Next, pour the mixture through a strainer or sieve into a clean bucket. The aim here is to remove all the rhubarb leaves. If you don’t have a strainer, use cheesecloth instead.
This can be a difficult and messy process—some people find a funnel helpful. If the pot you’re using is difficult to maneuver, ask another person to help you.
Press the rhubarb leaves that have gathered in the strainer so that as much of the liquid as possible drips down into the bucket.
Now that all the rhubarb leaves have been removed, they can be disposed of. It’s perfectly safe to place rhubarb leaves on a compost heap whether they’ve been boiled first or not.
Many people mistakenly believe that you can’t add rhubarb leaves to a compost heap because the oxalic acid levels are too high. Instead, the leaves’ oxalic acid is easily absorbed by other plants and quickly broken down during the composting process.
Even if that acid is still present when you add the compost to the soil, it’ll continue to decompose and won’t lead to a buildup of soil toxins.
If you don’t have a compost heap, place the rhubarb leaves on your soil or around your plants where they can decompose as an effective mulch.
Step 5: Adding the Detergent.
Now it’s time to add the dishwashing detergent to the rhubarb leaf infusion.
Mix one teaspoon of the dishwashing detergent with a cup of cold water. Stir this mixture into some of the infusion. A ratio of 1 part rhubarb leaf to 2 parts soapy liquid is ideal.
Alternatively, pour the soapy mixture into a clean spray bottle. Next, pour some, or all (depending on how much you have made), of the rhubarb leaf infusion into the spray bottle. Screw the lid on and shake the bottle, mixing the soapy liquid and the infusion thoroughly.
Clearly mark the spray bottle. You should also write POISON on the label to warn anyone who should unwittingly come across the mixture.
The remaining liquid can be placed in a seal-able clean jar or bottle. Again make sure that this container is clearly labelled as poisonous.
Freeze any rhubarb leaf infusion that won’t use in the next few days, as it loses potency quickly. Just remember to label the container clearly.
Also remember to clean any utensils and pots that you have used thoroughly. Place them somewhere safe, preferably away from the kitchen, so that they can’t be accidentally used in food preparation. While the risk of cross contamination in this way is low, it’s better to be safe than sorry.
Step 6: Applying the Rhubarb Leaf Insecticide
Carefully spray the rhubarb leaf solution on the affected plants. Make sure that you cover both sides of the leaf. If you chose to also spray the stem, take care not to spray any unaffected neighbouring plants.
The best time to apply the rhubarb leaf insecticide is on a dry, cloudy evening when there’s little to no wind. This means that there’s little danger of the wind blowing the spray onto plants that you intend to eat.
Applying the solution during the evening also means that daytime pollinators and other useful garden visitors such as butterflies and bees won’t be disrupted or harmed. Since the toxins break down quickly by the time the pollinators return in the morning, the chances of them being accidentally harmed are greatly reduced.
If you’ve never used a rhubarb leaf insecticide before, only apply it to a small part of the plant: one or two leaves at most. If successful, this test application will reassure you that the infusion won’t damage the entire plant.
You may have to apply the solution for two or three days consecutively before the infestation is completely gone.
Remember: don’t use insecticides made from rhubarb leaves on any edible plants. While the poison that makes the rhubarb leaf insecticide so effective can break down quickly, there’s always a risk that traces of oxalic acid will remain. Be safe.
As long as it’s used and stored in the correct manner, an insecticide made from rhubarb leaves can be an effective, chemical-free way to rid your prized blooms of unwanted visitors.