I’ve had a vermicompost bin for a few months now, and I was wondering if the worm castings would be good for my Meyer lemon tree. I decided to do some research and testing to find out more. Here’s what I found.

Worm castings are great for citrus trees as they’re one of the richest fertilizers available, do not have chemicals, and are odorless. They contain nitrogen, potassium, calcium, magnesium, and phosphorus, all of which are essential nutrients for citrus trees. You can use 2 cups of castings per inch of trunk thickness.

Worm castings act as an amazing fertilizer and are odorless (which is nice for you), but what are the specific benefits for citrus trees?

Are Worm Castings Good for Citrus Trees?

Tyler holding worms over his Meyer lemon tree

Worm castings highly benefit citrus trees due to their improved water retention, disease maintenance, and even pest reduction. While worm castings have a neutral pH of 7, citrus trees prefer a slightly acidic pH of 6.0-7.0, so adding some coffee grounds, peat moss, or sand will improve the soil’s acidity.

If you have dry soil, consider using worm castings along with your compost or mulch. Worm castings help with water retention in the soil and they also inhibit root disease and rot so you don’t have to worry that the excess water will lead to rot.

Not only do worm castings have a neutral pH, but they also help protect plants from pH levels that are too high or too low in the surrounding soil. However, this can be a slight drawback in plants that require acidic soil, such as citrus trees.

Since citrus trees need soil with a pH of 6.0-7.0, be sure to take that into account when using worm castings with your citrus trees.

Worm castings also act as natural soil aeration. The castings are tiny, round objects that decompose in the soil, which leave behind pockets of air. The healthy soil then attracts more earthworms, which will continue to tunnel and add to the soil aeration.

Compared to chemical fertilizer or manure, worm castings are much more fast-acting. If you are harvesting your own worm castings, it takes a while to build up enough worm castings to effectively use.

Tylers vermicomposting bin
My vermicomposting bin

If do harvest your own worm castings, keep in mind that it can take around three to six months of feeding the worms to harvest enough castings for use.

In this way, it takes a long time, but once they’re applied, they can be accessed by the tree almost immediately.

I can vouch for this as I applied 1-2 inches of vermicompost to the top of my potted Meyer lemon tree several months ago and it started dramatically growing new branches and leaves within just a few days (see the image below-the shiny leaves are the new growth).

New growth on Tylers potted Meyer lemon tree

On the other hand, fertilizer and manure need time to be broken down in the soil before they can be used by the plant.

It may a while, but harvesting your own worm castings (called vermicomposting) is cheap, odorless, can be done indoors, can be done year-round, and will reduce your household waste.

There are a few different options for how vermicomposting can be done, so if you’re considering making your own, check out this short video I made about how to start a vermicompost bin within 10 minutes and for under $50.

If composting and maintenance of worms don’t sound too appealing to you, don’t worry. Worm castings are sold all over the place with plenty of online buying options as well as being sold at many gardening and farming supply stores.

Castings are becoming a more popular option for fertilizing, so luckily it’s getting easier to find if you’d like to simply buy it.

Which Nutrients Are in Worm Castings?

The primary nutrients in worm castings are nitrogen, potassium, calcium, magnesium, and phosphorus and the secondary nutrients include copper, zinc, iron, carbon, nitrogen, and manganese. Together, these nutrients benefit the overall health of the tree, along with its flowering, fruiting, and disease-resistance.

The three main nutrients needed by plants for healthy growth are nitrogen, phosphorus, and potassium which are all found in worm castings.

Citrus trees also need micronutrients (trace elements) found in worm castings like iron, magnesium, manganese, and copper. Worm castings supply just about all of these nutrients in sufficient volume, without the unwanted excess chemicals.

What makes worm castings so healthy for plants? Well, there are a huge amount of nutrients, minerals, and healthy bacteria packed into these small disks.

In case you’ve been wondering what exactly worm castings are, they’re simply worm feces. While it may be gross, earthworms are decomposers, so their droppings are concentrated and ultra-nutritious for plants.

The castings are also water-soluble, meaning the nutrients in them can be absorbed very easily while the plant’s root systems take in water. This is why worm-tea is very popular to use when fertilizing plants and reviving dead soil.

Other than the primary and secondary nutrients, other things can be found in worm castings such as bacteria (the good kind), enzymes, some remnants of plants and animal manure, and earthworm cocoons.

While bacteria in fertilizer may sound unpleasant, it’s actually helpful bacteria similar to what can be found in human digestive systems.

Also, earthworm cocoons are quite helpful because not only do they help with aerating the soil, but will also hatch new earthworms in around two weeks, which continue the decomposing process and produce more worm castings.

How Do You Apply Worm Castings?

For citrus trees, there are three steps to apply worm castings:

  1. Use two cups of worm castings for every one inch of the diameter of your tree.
  2. Apply a layer of castings over the existing soil, away from the trunk of the tree but all the way to the drip-line (under the citrus tree’s canopy).
  3. Cover the worm castings with a 1-2 inch layer of mulch or compost and water the area.

This process should be repeated at least once or twice a year (ideally just before the growing season).

Also, check that you place worm castings about two inches away from the trunk of the tree. Since worm castings are so good at retaining water, the theory is that putting worm castings too close can lead to the trunk getting too moist and rotting.

Another option for applying worm castings would be mixing a pound of castings into five gallons of water and watering your tree with this “tea” four times per year.

The method is up to your personal preference but both ways are effective and both will get those much-needed nutrients to the tree. 

Typical fertilizers should be applied to citrus trees about once a month during active periods, so the infrequency needed for worm casting proves just how effective they really are.

Know that even with applying them less often, worm castings should have better results than a normal fertilizer would. 

Also, keep in mind that applying worm castings is specific to the type of plant you’re working with. For most plants, you can mix in worm castings with the soil and then either top-dress or side-dress the plant in intervals such as every two weeks, every two months, or even once or twice seasonally.

If you’re interested in using worm castings for your citrus trees, check out this video that compares worm castings to compost as well as explaining how worm castings work and how to farm them.

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