An effective treatment that is easy and safe to use on house and garden plants.

Diatomaceous Earth is a natural and effective way of ridding plants and citrus trees of common garden and glasshouse pests, including mealy bug, spider mite, scale insect and aphids. At our plant nursery in East Sussex it has been our preferred method of treatment since 2022 and here we explain the simple steps you can use to apply this product at home.

Why we recommend diatomaceous Earth

As a treatment for using at home it has several benefits.

• Effective
• Eco-friendly
• Easy to apply
• Reasonably priced
• Gentle option for plants that are sensitive to soap/essential oil/chemical treatments
• Safe to use around pets and children (with some precautions)

How diatomaceous Earth works

diatomaceous earth is basically made from ground up fossilised aquatic creatures called diatom. It is naturally occurring and usually found in river beds or dried up ocean beds. Similar to sand the main element in the exoskeleton of these tiny creatures is Silica and it is the drying characteristic that this powder has on the fats and cuticles of the plant pests and the 'sharp' edges of these microscopic shells that cuts and irritates the pests that feed on our plants. It will work on any soft bodied insect, so shouldn't be used at the same time as 'good' predators or around pollinator feeding areas but it is safe to use around most flying insects like bees and hoverflies and at the same time the sharp pieces are too small to be anything other than a mild irritant to humans, dogs, cats and babies. It works best when it's dry so although it is easiest to apply with water in a spray form or by dunking, it works best when it's dried out and left a fine powder behind on the leaves and stems of the plant. Any insect that walks or crawls over this fine dust will be cut and damaged by the sharp edges and will die off before they have the chance to reproduce. In large pest infestations it can take more than one application to break the life cycle and destroy all of the insects and eggs on a plant but it works on insects at all stages of their life cycle from egg, through adolescence to adulthood. For treating small, targeted areas it can be dusted straight onto the affected area. For treating whole plants a solution made with water and a small amount of liquid soap will allow for fast treatment and total coverage. The soap itself acts as a treatment agent preventing insect pests from respiring and moulting, then once the solution dries out a fine film of the diatomaceous earth is left behind on the leaf and stem surfaces for prolonged treatment action on pests.

How to apply Diatomaceous Earth as a treatment for Scale and Mealy Bug

Using Diatomaceous Earth as a bug spray

You will need:

• Diatomaceous Earth (Diatom) – A completely natural and organic treatment so safe to use on edible plants. Diatomaceous Earth 150g Our friends at Andermatt sell this at a reasonable price
• Spray bottle or Garden pressure sprayer
• Ecover washing up liquid or horticultural soft soap- this is kinder to the plant and fruit than regular washing up liquid.

PLEASE WERE A MASK OR SPRAY IT OUTSIDE IF ASTHMATIC OR HAVE ANY BREATHING PROBLEMS. Generally, it is okay to use without a mask if outside, and is used for many things including treating pets for fleas, but if someone is sensitive to fine particles it is better to be safe than sorry.

Method:

1. Add 1 tablespoon of the diatom to 1 L of water and shake to mix well. Add 1 teaspoon of Ecover washing-up liquid or horticultural soap and stir to mix well.
2. Use this solution to spray the plant all over – over and under the leaves, in the stem and leaf joints, on the branches and the soil, on the fruits – basically everywhere. Young mealy bugs and scale insect can be difficult to see without a microscope and so it is important to completely cover the entire plant and soil with the solution.
3. The diatomaceous earth won’t dissolve into the water and so will start to separate out and sink to the bottom and so shake the sprayer regularly.
4. Spray the tree in this way twice within the space of a week, and repeat for a second week.
5. Three days after the final treatment, the dead pests can be removed from the plant – wipe off with cotton wool pads or baby wipes dipped in water.

You should treat your tree twice a week for a couple of weeks, make sure you wipe off as many of the insects as you can while you are waiting for the diatom earth to arrive, so it is easier to keep an eye on. It will not cause any damage to your plant whatsoever. Also, you probably have quite a few microscopic babies all over your plant too, but they will be so small that you cannot see them with the naked eye, so it is very important to thoroughly soak the whole plant with this solution, it will only work if it touches the pests.

This treatment will work for almost all plant pests, including Spider mite, Cotton Cushion scale, Scale, Thrips, Caterpillars and Aphids, Mealy Bug, so even though you will not use much of this for treating this plant it is a fantastic pest treatment staple to keep to hand for the next pest invasion. It is worth noting that you should always treat your plants before you bring them back in for winter, it will help avoid an attack next winter, and if trying on a different plant, do a patch test first, and leave it for a couple of days, some plants are more delicate than others and can get damaged leaves from the soap or the earth.

Using diatomaceous Earth to treat heavy pest infestations

If you have a lot of scale or mealy bug on your plant you might find it simpler and easier to make up a big bucket of diatomaceous Earth solution and dunk the entire plant into the solution. This method is particularly useful on these more persistent pests, if you are short on time or have more than one plant to treat but it does involve a bit more space and equipment.

Ideally you want to use a bucket big enough that you can submerge the entire plant in a soapy water and diatomaceous earth mix for half an hour, twice a week, for 2 – 3 weeks at least, for a very bad infestation it might take much longer.

If you do not have a bucket big enough, then hold the plant upside down and swish the whole head of foliage for 5 minutes, and then sit the pot upright in the solution for the other 25 minutes. Do this in a shady spot to avoid scorching the foliage. Do not leave it standing in the water for any longer than the half hour. Once times up take it out and let it drain away all the excess water.

How to apply diatomaceous Earth on sensitive plants

We have trialled the method above extensively on all varieties of citrus trees and many houseplants and would recommend it's use on most plants however there are a couple of plants that do not react well to the soapy water or Ecover in the method above. For Curry leaf plants, Dipladenias, Orchids and other particularly soft leaved and/or sensitive plants we would recommend leaving the Ecover or soft soap out of the mixture. If in doubt you can always do a trial treatment on just one leaf or branch to ensure it's not going to have a negative affect.

Tried and tested at our Sussex nursery

At Plants4Presents working with the environment has always been important to us so we've never used chemical sprays or treatments but over the years we have tried and trialled a number of different organic and natural pest treatments. At our nursery in East Sussex we have over 2 acres of glass and up to 8,000 plants on site at any one time, including several thousand citrus trees. Despite our best efforts, we will always find the odd pest that's found it's way into our nursery and in these nice warm, sunny and moist conditions with plenty of delicious plants to feed on, they will multiply like crazy if we don't act fast. We find that predators are excellent for controlling white fly, thrips, spider mite and to some extend aphids and mealy bug but in a greenhouse of this size with so many tasty citrus trees we don't find that predators are effective enough on citrus scale and mealy bug. After all we sell plants as gifts, so we have to be absolutely sure a plant is free of all pests including eggs and larvae before sending them out to a customer.

In 2021 Laura joined us with a strong background in pest control and plant science so we decided to get a bit more scientific about which of the organic pest control methods would work best for us in our nursery environment and with the particular range of plants we sell. We had used neem oil in the past, but found it unreliable in its effectiveness and had since been mostly using soapy water solution sprays. This was effective, but 2 main issues we found were that it sometimes required many repeat treatments to be effective, and couldn’t be used at all on some of our more sensitive plants as it scorched the leaves. Our Nursery Manager, Libby read about diatomaceous earth and bought a small amount to trial on our plants. Initial tests showed promising results of quicker and more thorough pest eradication than we had seen with either neem oil or soapy water and so we decided to trial it properly. We took a cross section of our plants in our quarantine area and treated a range of different plant species, with a range of different pests, with 3 different diatomaceous earth treatment methods

1. neat diatomaceous earth dusted directly onto plants,
2. diatomaceous earth solution with minimal amount of soap used as an emulsifier
3. diatomaceous earth combined with a treatment concentration of soap (15mL soap per 1Lwater).

This process allowed us to test three main elements;

1. what the most effective concentration and method of using diatomaceous earth was
2. whether it could safely be used across a range of plant species without causing damage to the plants themselves
3. whether it was effective across all of the main pests encountered in our nursery.

Over several weeks of treatments, we found that 3 applications per treated plant using a mixture of diatomaceous earth and Ecover liquid soap resulted in considerably fewer pests, indeed most of the plants treated using this method were able to be signed off as completely pest-free. Though plants treated with our existing mixtures of neem oil or soapy water also had reductions in the number of pests present, our trial with diatomaceous earth and soapy solution proved it to be our clear (and actually, surprise) winner. It is effective across a range of indoor and outdoor plants and various different pests including scale, mealy bug, cotton cushion scale, spider mite, thrips and aphids and it is our most versatile treatment agent, as it can either be used on its own for more sensitive plants, or in combination with soapy water for a double pronged attack on pests.

DISCLAIMER To be clear for all you science buffs out there, we had tried to ensure that the plants and level of infestation were similar in all treatment groups but this is quite a subjective call, the temperature that year, the spray/dunking methods we were using, and the concentration that we were using could all have had an affect on the end result. These trials had to fit around other pressures in the nursery so the number of days between treatments might sometimes vary and we didn't have a strict control group. To really draw a scientific conclusion of which is the 'best' method of treatment you would need to do a much larger and more controlled studies of the 3 methods against a control group, receiving no treatment. For us the conclusions were striking enough for us to change our treatment methods though and we have been recommending this method to our customers ever since, who report similar success.

Where to buy Diatomaceous Earth?

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You can also buy diatomaceous earth online at and at most good garden centres.For more advice on looking after citrus trees generally, head back to our main plant care page or get in touch with us.