Whether you are potting indoor plants or building outdoor grow boxes, cultivating strong plants is all about creating a healthy growing environment. A good potting mix with the right combination of organic matter and compost will give your plants the foundation they need to thrive.
We recommend using an organic potting mix instead of potting soil. Potting mixes are engineered using sterile materials, they have fewer nutrients and very little biological activity so you have more control of your growing environment. Compared to soil, potting mixes will retain moisture more effectively while ensuring that there is enough airflow to keep plants from flooding.
Soil tends to hold more moisture, so in a container it can cause plants to become waterlogged. Potting soil can also introduce weed seeds and insects to your plants. Since raised beds generally have an open bottom, water drainage is typically not an issue. However, topsoil with too much sand won’t hold water well enough, and soil with too much clay will hold excess water. If you are going to use topsoil in your raised beds be sure it contains less than 30% clay, <70% sand and <70% silt. And don’t forget to amend your soil to ensure that it has the proper nutrients to support plant life.
When choosing a potting mix, find a clean, organic potting mix that doesn’t include any harsh chemicals or ingredients like styrofoam or additional fertilizer.
Adding pollutants like Styrofoam to your growing environment will only pollute the ecosystem. Styrofoam is classified as a Non-Biodegradable Pollutant, and it takes 500 years to decompose. We don’t believe that any non-biodegradable ingredient belongs in your soil.
We recommend using a fertilizer-free mix so you can control your nutrient inputs on an as needed basis, rather than just relying on whatever happens to be in the mix. Fertilizers can lose their potency over time. There is no telling how long that fertilizer has been sitting or how potent it still is at the point of application.
Once you make sure that your potting mix has the right ingredients, be sure to grab a bag that is dry and light. Waterlogged potting mixes can rot and diminish in mineral value. In addition to your potting mix, it is best to combine your mix with nutrient rich compost and clean, coarse sand.
Composting is a perfect way to put organic waste to work for you. Whether you want to start a Vermicompost or a Thermophilic compost, check out these tips to get the most out of your compost.
Sand is a great way to prevent overhydration, add some air to your compost mix and create a strong environment to support your plant growth. We recommend using coarse sand. Overly refined sand will make your mix too dense and prevent air and moisture flow.
For pots, containers and planters combining potting mix with compost for top dressing is ideal. We recommend using 60% coconut coir or potting mix, 20% compost and 20% sand. If you do use coconut coir, be sure to rinse well before adding to your planter or pot. For plants like succulents that don’t require as much water, try upping the sand to 25% or 30% of the overall mix.
Sometimes for outdoor growing boxes or raised beds, people will utilize bulk topsoil. Unfortunately, the topsoil health is so compromised that in most instances you’ll still need to add compost that is rich with organic matter to replenish the overall soil health. Instead of topsoil, we recommend using the same 60% coconut coir or potting mix, 20% compost and 20% sand in your raised bed to start a thriving growing environment. With an open bottom raised bed, water will drain more freely so you won’t need to be as selective when watering – even if you do use soil.
Erler, E. What is the best soil for potted plants? University of New Hampshire Cooperative Extension.
Smith, T. and D. Cox. Bagged potting mixes and garden soils for home gardeners. University of Massachusetts Amherst.