Filling Pots, Containers and Raised Beds: How to Use a Soil Calculator

Fall and spring signal it’s time for a few garden tasks. Filling new or old gardens with fresh soil is important and has long-lasting benefits. Fresh amendments contribute to a healthy belowground microbiome, which is crucial for disease and pest resistance. It bolsters your ornamentals and crops with nutrition, live organisms, and air around their roots.

Maybe you’ve guessed how much soil you’ve needed in the past and came up short, or this is your first time amending raised beds. Whether experienced or beginning, a soil calculator is an efficient tool that removes guesswork. Use it to know exactly how much mulch you’ll need depending on your garden’s size.

Measure Your Garden Containers

Most American tools measure by cubic yard, foot, or quart, while others utilize the more standard metric system. They all need the container’s height, length, and width to give you an accurate reading. Once you have all these details, you can plug them into your soil calculator.

Don’t worry if you have circular pots; there are measures for circles, rectangles, and squares. Circle calculators require the pot’s diameter and depth to deliver a proper reading. Use a tape measure, ruler, or phone application with one of these tools. 

The depth measurement determines how many inches or centimeters of soil you’ll add to your pots, containers, or raised beds. Measure the empty beds’ entirety as they need a thick, fresh layer. Old beds only need enough to fill them to their tops, so use their unfilled space for the depth measurement.

Select Soil Type

Different soils are more or less dense depending on their particle size. Generic calculators measure soil, or compost, while others have presets for mulch and amendments. New beds benefit from a balanced mix, while old containers appreciate extra compost. 

You’ll want half or less of your mix to be a rich organic amendment like compost or leaf mold. A soilless mix is excellent for the other half of the mix, as it balances the high nutritional content of compost. Choose a premade soilless mix, or make your own with amendments like coco coir, perlite, and horticultural sand. 

Some common, affordable mulches for ornamental crops are wood chips, shredded wood strips, and pine needles. Crops need more nutrient-rich amendments like compost, leaf mold, or farm animal manure. 

All soils appreciate organic matter, which inoculates soil with worms, bacteria, fungi, and a whole array of living organisms. Ensure at least 25% of your mix is compost for happy, thriving plants. This decomposed organic matter helps the medium hold and drain water well during drought or excessive rains.

Choose Pots or Beds

Soil calculators work differently for containers than for raised or in-ground beds. You’ll want to calculate the two separately first, then add their sums at the end. That way, you’ll buy or make enough soil to fill both to the top.

Container calculators use smaller measurements and reduce the amount of fertilizer added. Potted plants live in their soil bubble, so they don’t battle for nutrients like those growing amongst other species. Raised beds needs extra fertilizer and compost, so the calculators account for these in their results. 

With your container and bed measurements separate, you’re ready to start calculating! Plugging in the length, width, and depth values is the easiest part of the process. Gather your measurements and get ready to calculate.

Calculate!

Calculating online is as easy as hitting a button. Most tools have you plug in the length and width of your beds. Some allow you to put in the area of your space instead of the length and width. Use one of these tools if you prefer finding the area yourself. I like it simple and use the ones that measure the area for you.

After the area plugin, put in the depth of your beds or pots. Some calculators have you select a soil type. Use “soil” for compost if no compost label is available. Otherwise, choose the amendment type you’ll be adding to your garden.

With all these values in the calculator, hit “calculate” and record your results. You’ll discover how many cubic feet, cubic yards, or quarts of soil you’ll need. If the number seems extravagant, start over and remove the values. Plug them in again to make sure all is correct. If it still seems off, measure your garden again and compare the results.

Buy Topsoil or Mulch

With the total number in your hand, you’re ready to find some dirt! I recommend looking for organic topsoil mixes from local nurseries near you. If you’re using a ratio of your own, find individual amendments that don’t have other products mixed in. Then, blend them at home yourself. This greater level of control helps you discover the perfect mix for your ornamental or edible beauties.

There are plenty of online retailers that sell mixes if you live far away from a nursery. They might be more expensive, although they deliver right to your door! Scour over the specifications to ensure what you buy is what you get. 

While shopping, look for an organic fertilizer with mycorrhizae in it. Use it in your mix and it’ll inoculate the bed with beneficial microbes and nutrients. 

Use Homemade Compost

Instead of spending money on mulch or other amendments, try creating homemade compost! It’s a free amendment that recycles kitchen scraps, plant debris, and grass clippings into black, crumbly dirt. This amendment is an important part of a healthy belowground ratio, adding organic matter and microbial activity wherever it lies.

Beginning compost is easy enough—mix an equal ratio of dry, brown material with fresh, green material in a pile at least three feet wide and tall. Turn the pile daily, watering it to be moist like a wrung-out sponge. After a few weeks to months, your debris will have morphed into humus-rich compost.

There are many ways to compost besides making a pile. Totes, tumblers, and bokashi bins are all excellent ways to turn waste into an organic amendment. Find a solution that works best for your setup. If you lack yard space, try bokashi composting; the process ferments waste so it decomposes more readily when you bury it outside. 

Repeat Every Fall or Spring

Soil compresses over time as roots decompose, rain erodes the dirt, and creatures step on it. You’ll especially notice compression in raised beds and containers, as gravity and irrigation make it look like the soil is shrinking. 

Grab your trusty soil calculator and plug in the numbers during fall, spring, or both seasons. Even if you’re not ready to buy more, you’ll know how much you’ll need to purchase in the future or make yourself with compost. 

In-ground beds need top-offs less often, although they appreciate heaping helpings of compost throughout the year. Layer two or three-inch coatings whenever it’s available. Your vegetables and wildflowers will thank you with dozens of fruits and blooms.