When you set out for the garden center to load up on supplies, it can be a little overwhelming. So many choices and sometimes, there’s limited staff to guide you as to what to choose and why. It can also get pretty expensive – fast.
What To Choose
When you are looking for soil in a garden center, there are typically three main types: top soil, garden soil and potting soil or potting mix. Top soil is a mix of sand, silt and clay. It may contain other things, but it is not nutrient-rich or high in organic matter. This is typically used to fill in holes, level an area, or to mix with compost and other healthy goodies to add to a garden soil. Garden soil is mainly top soil mixed with compost. Use this for raised garden beds and amending the soil in your yard for planting gardens or landscape plants. Potting soil is actually not soil at all which is why it may be labeled as potting mix. It is a soil-less mixture of light, fluffy and fast-draining materials that provide a good environment for plants to grow in containers. Some basic ingredients are coconut coir, peat moss, perlite, vermiculite, compost and fertilizers. There are different blends for different types of plants and for starting seeds, each with their own water holding capacity, texture (particle size), and nutrient content.
If you have a lot of containers that you want to plant, you would likely save a lot of money by purchasing the ingredients to make your own potting mixes at home. You’ll save even more money if you are making a good quality homemade compost or vermicompost (worm compost).
You can easily make your own potting mix with a few simple ingredients, a wheelbarrow or tub of some sort for mixing, a shovel or trowel for mix, and a storage container for any potting mix that you aren’t going to use immediately. A tote with a lid works – you want something to keep the potting mix closed and dry.
Coconut coir is a by-product from coconut processing. It is used as a substitute for sphagnum peat moss because it is more eco-friendly and doesn’t lower the pH of the soil. It is often sold in compressed bricks that you would re-hydrate by submerging them in a bucket of water (rain water is best). The coir will get fluffy and crumbly after about an hour, allowing you to scoop or pour it out of the bucket. PRO TIP: Add your other ingredients to the bin first except your granular fertilizer if you are mixing that in. That way, any excess water will be easily absorbed into your potting mix. If you are storing this for use later, try to minimize the amount of water in your coir. If you’re using it immediately, the excess moisture in moderation is fine. It does have more nutrients than peat and is more sustainable, so I choose to use coir personally. However it is more expensive.
Sphagnum peat moss is a natural material that is harvested from old peat bogs. It takes thousands of years to form, and is actually one of the biggest carbon sinks (places that sequester carbon underground) so it isn’t a sustainable product. It is sold in compressed bales that are surprisingly light-weight making it a very popular choice for potting mixes. Peat does lower the pH of the soil so you’ll need to add a bit of limestone to the mix. It also has very little nutrient value for your plants – adding fertilizer and good quality compost are important.
Vermiculite is a powdery substance that is actually a mined material. It is light weight and is added to increase pore space and water retention of your potting mix. Vermiculite also adds calcium and magnesium. Be sure to wear a mask or handle vermiculite in well-ventilated areas outdoors, and don’t stand up-wind of it as you are pouring and mixing.
Perlite looks like small Styrofoam balls in your potting mix but it isn’t. It’s actually another mined material. It is light-weight and also improves your soil’s water holding capacity and drainage. It is neutral in pH. Many people add perlite to raised garden beds to prevent compaction.
Compost is decomposed organic matter that you can make at home, get from a friend or purchase in bags. It is rich in nutrients and full of beneficial microbes that actually help your plants take in minerals and water from the soil. Compost will also help your soil retain water. Because of this, you don’t want to fill containers up with 100% compost. It will be too heavy for healthy plants, however, it is great to add to potting mix to add nutrients. It will need to be screened or sifted of any large pieces of mulch that haven’t broken down. If you are using it to start seeds, you’ll need to sift it with a much finer screen so all of the particles are very small – maybe 1/8 of an inch hole size.
Vermicompost is actually worm poo. It’s made by specialized worms that eat food scraps. You can make this at home by having a vermiculture bin sometimes referred to as a worm farm or you can purchase it from a store in bags. Like compost, it is high in nutrients, beneficial microbes and helps your soil to retain moisture. A little goes a long ways, so if you are making this at home and only have a cup or two to add to your containers, that’s quite okay. It’s very powerful stuff – in a good way.
Sand is an important ingredient in potting mix for trees, cacti, and shrubs. If you are planting plants (such as many Florida natives) that prefer a less fertile soil, adding coarse sand will help those plants to feel more at home in their new container. If you’re looking for sand to purchase, avoid getting Play Sand, which is too fine and will end up making your potting mix too dense. Coarse sand or builders sand is preferred.
Lime or Limestone is a powdery substance made from crushing limestone. If you have a choice of products, it is probably between either calcitic or dolomitic limestone. The biggest difference is that calcitic lime contains only calcium while the dolomitic lime has both calcium and magnesium. Both are necessary for plant growth and fruit production BUT adding lime does change the pH of the soil. You will usually only use a tiny bit and then usually only if you are using a peat moss product in your potting mix or you take a soil sample that indicates your pH is too acidic (low).
Wood chips or mulch can be added to mixes for some plants, particularly composted wood chips rather than fresh so they have already started to break down. This is a common ingredient in potting mixes for woody plants – shrubs and trees. Do not add composted or un-composted wood chips to potting mixes for annual vegetables or herbs. The partially decomposed wood will continue to break down, using nitrogen in the soil in this process. You can compensate for this by adding some grass clippings or legume (bean or pea) leaves to the surface of the soil and topping with mulch and/or adding blood meal or alfalfa meal to the soil mix. They will all supply some extra nitrogen to balance the wood chips’ use of it. A nitrogen deficiency in plants is usually evidenced by yellowing leaves starting at the lower leaves.
Fertilizer is important to add to a DIY potting mix, especially if it is peat-based therefore lower in nutrients. You can add an organic time released granular fertilizer or you can use a number of different natural products to add nutrients to the soil. Bone meal is released slowly into the soil (takes 6-8 weeks) and will add phosphorus and calcium to the soil and is good for root development. Blood meal will add nitrogen into the soil. This will help with leaf development and make plants greener. Alfalfa meal or pellets are good for nitrogen as well. Sea kelp in powdered or liquid form or rinsed seaweed adds micro-nutrients to the soil (think Dead Sea mud mask for your garden).
As always, read the labels on products that you buy to make sure you are using the proper amount. In many cases, a little is all you need and more is not better. There are also natural products such as fish emulsion and liquid sea kelp that you can add to plants periodically during the growing season to boost their nutrient availability.
DIY Potting Mix Recipes
Our unit of measure here is gallons because we usually pour ingredients into 5 gallon buckets and measure. You can divide a 5 gallon bucket into 5 parts and mark it off with permanent marker dashes to help you make your measurements more precise, or you can guesstimate. If these quantities don’t suit your needs, switch the word gallons to parts and use any unit (larger or smaller) to make the amount of potting mix you need.
We highly recommend using coconut coir rather than peat for sustainability purposes. If you decide to use peat instead, substitute it in equal amounts for the coir and add 1 heaping tablespoon of lime per gallon.
While mixing, wear a face mask to avoid breathing in any airborne particulates. Soil and compost borne diseases are real, and vermiculite and perlite dust are not good to inhale. Safety glasses and gloves should also be worn. Don’t make your potting mix on a windy day.
Basic Potting Mix for Vegetables, Herbs and Plants that Like Nutrient Rich Soil
4 gallons soaked coconut coir
2 gallons perlite
2 gallons vermiculite
6 gallons sifted compost
2 cups vermicompost if available
Fertilizers specific for your plant needs (total of 1 cup)
Seed Starting Mix
1 gallon coconut coir
1 gallon vermiculite
1 gallon perlite
1/2 gallon sifted compost or worm castings
Blueberry Potting Mix (and other Acid Loving Plants)
1 gallon compost
1 gallon perlite or vermiculite
2 gallons pine fines (partially composted and shredded pine) or composted pine bark
1 cup fertilizer blend – blood meal, bone meal, sea kelp
Coffee grounds can be added periodically to the surface of the soil
Cactus and Succulent Mix
2 gallons coconut coir
1 gallon perlite
1 gallon vermiculite
2 gallons coarse sand
Woody Plant Potting Mix (Trees and Shrubs)
2 gallons coconut coir
2 gallons composted bark (which can be sifted from compost)
2 gallons compost
2 gallons coarse sand
2 cups fertilizer blend