Applying worm castings to your soil is one of the best ways to fertilize, supplement the soil, and provide beneficial microbes to your plants.

While you may be aware of worm castings in general, it can be confusing to know how much to apply. How much do you need to use for your soil?

Simple Grow Soil is here to answer in detail.

Methods of Applying Worm Castings

When you apply worm castings, there are a few different ways that you can do it. How you apply will determine how much worm castings you should use for that method.

One thing to keep in mind is that you can’t really use too much. So even if you use all of the different methods of applying worm castings at the same time, you won’t hurt the plants. In fact, you’ll provide the best possible results for your plants. Just in case you don't know what they are, you can find out here: what are worm castings?

Because of that, the amount that you use for your soil will differ from one case to the next. 

• Broadcasting - Broadcasting is a method where you spread it around on top of the garden or soil by hand or with a spreader. Many people use hand-held seed spreaders when doing a smaller area like this. If you’re doing a large area, you can get an industrial size spreader. When applying worm castings to the soil in this manner, using about 15 pounds of castings per 100 square feet is typical. 
• Mixing in the soil - If you’re applying at the time of planting, mixing the castings in with the soil is an ideal method of application. When using this procedure, plan on putting in at least 30 pounds per 100 square feet of soil. Again, you can’t put in too much, so apply as liberally as possible. For weed soil questions, check out our detailed guide.
• Top dressing - Top dressing is a method that some people like to use when they’ve already planted and they want to concentrate the benefit of the castings right on the plant. With this method, you should apply about half a cup of worm castings around the base of each plant. How much you apply will depend on how many plants you have in your garden area. 

Worm Casting Tea

Another option to think about is applying the worm castings to your soil in a liquid form. Many people like to use this option instead of applying the castings in dry form. The big advantage of this method is that you can make your castings go a lot farther than normal.

For example, it takes about five pounds of worm castings to make five gallons of worm castings tea. That five gallons can then be sprayed on up to one acre of soil, grass or plants.

Even if you doubled up the application ratio and used 10 gallons of worm casting tea to an acre, you’re still only utilizing 10 pounds of castings. That’s much less than you would use if you applied with any of the dry application methods listed above. 

While you can make the castings go further with worm castings tea, there are some drawbacks to consider. The castings tea does transfer the beneficial microbes from the castings to the soil. However, you don’t get many of the other benefits that come with traditional worm castings.

For one thing, you won’t get any of the aeration that comes from mixing castings into the soil. You also won’t get the moisture retention and regulation that comes with putting castings into the soil.

The microbes also won’t last as long as if you put the castings into the soil. This means that you’ll most likely need to reapply more often when using this approach.

Another potential issue with using worm castings tea is that it requires some additional preparation time and equipment. To make worm castings tea, you need a worm castings tea kit. You’ll also need some kind of a sprayer to apply it to the soil.

Additionally it takes 24 hours to make the tea every time you want to produce a batch. So if you have a five gallon worm tea kit, you’ll need 24 hours every time you want to make five gallons of tea. If you have a large area, it’s best to get a larger, industrial-size tea kit. 

Hybrid Approach

The ideal way to help your soil and plants is to utilize a hybrid approach to applying the castings. Start out by making worm castings tea and spraying that on the soil before you plant.

Drenching the soil with worm castings tea will get the microbes into the soil and help enrich the natural environment for your plants. Then mix worm castings into the soil as you’re planting. 

Whichever method you use to apply, always overestimate the amount that you think you’ll use. You can either apply a little more than you planned, or save the rest and apply more later. Your plants will absolutely love the castings and thrive because of the microbes and nutrients that they provide.