Packaged potting soils offer undeniable convenience, but the expense can quickly accumulate in a bustling garden. Looking ahead to the upcoming year, as my stockpile of decomposing sawdust reaches maturity, my aim is to achieve self-sufficiency when it comes to potting soil.
This endeavor promises not only to lighten the load on my wallet but also to benefit both my plants and the environment. Moreover, it offers the added convenience of having a ready supply of potting mix whenever it’s needed. If you have access to soil and compost, you possess the fundamental elements required to craft your very own potting soil.
In lieu of relying on peat moss, perlite, and vermiculite—the three primary components found in commercially available potting soil—you can effortlessly blend your high-quality soil with well-cured compost, leaf mold, decomposed sawdust (obtained from untreated wood), or a diverse array of other organic constituents.
Begin with modest batches, supplement them with store-bought mixtures to extend your reserves, and gradually transition towards the ideal vision of potting soil—a straightforward, nurturing medium conducive to the flourishing of robust plants and the successful germination of seeds.
A few words about ingredients in your potting soil
A substantial portion of any homemade potting soil blend consists of compost, while commercial potting soils predominantly rely on a combination of peat moss, perlite, and vermiculite. Regrettably, the extraction, processing, packaging, and transportation of these commercial components contribute to land degradation and pollution.
Peat moss, for instance, is harvested from wetland bogs in regions like Canada or Michigan, a practice that isn’t environmentally sustainable and is often conducted far from your local area. Many nurseries specializing in woody shrubs and trees have discovered that composted tree bark or wood chips make excellent substitutes for peat moss.
Coconut husk fibers, known as coir, are a readily available substitute for peat moss, but they may be considered exotic unless you reside in the regions where they are produced, such as India or Central America.
For most of us, practical alternatives to peat moss include leaf mold (composted leaves), decomposed sawdust, or a blend of both. It typically takes around two years for a 4-by-5-foot pile of chopped leaves to decompose into leaf mold. In areas where organic rice or other grain hulls are abundant, composting them can yield a lightweight material ideal for enhancing potting soil texture.
Vermiculite, another commonly used potting soil ingredient, is fraught with environmental concerns akin to peat moss. Deposits in Montana and Virginia have been found to contain asbestos, making a small area of South Carolina the sole safe source in North America.
Perlite ore, mined from mountain plateaus spanning from New Mexico to Oregon, undergoes a lengthy journey before reaching your garden. Its primary contributions to potting soil—improving texture and drainage—can often be matched by clean sand. To create a lightweight mix, a small amount of sand per quart is sufficient. As a precaution against slow drainage in the lower regions of seedling flats or containers, a thin layer of rotted leaves, sawdust, or sand serves as an effective remedy.
Using live compost
Incorporating live compost or biologically active garden soil into your potting mix often involves two additional steps: screening and subsequent heat treatment or pasteurization, usually at temperatures ranging from 160 to 180 degrees Fahrenheit.
My preferred method is to utilize compost derived from garden waste for making potting soil. When a batch of compost appears promising, I screen it and store it in various containers like plastic pails, bins, or bags (recycled from previously purchased potting soil).
My compost screen consists of half-inch mesh plastic fencing securely fastened to two pieces of scrap lumber. Many individuals employ a similar setup, attaching the screen to a sturdy wooden frame. Stored in a location where it can maintain slight moisture, screened compost continues to mature and enhance in quality over time.
If you possess high-quality, well-cured compost and you’re not dealing with delicate, light-stressed seedlings (known for their vulnerability to diseases), you can confidently prepare a 50:50 blend of compost and good soil and give it a try.
Alternatively, you can opt for a mix with more compost and less soil. In my case, the compost made from garden waste frequently contains a substantial amount of soil, primarily from the roots of uprooted plants. As a result, I often opt for a ratio of 3 parts compost to 1 part soil when potting plants that are ready for a nutrient-rich, earthy mixture, providing them with a taste of their future growth environment.
However, it’s important to be aware of potential risks. Compost’s bioactive nature makes it an excellent primary food source for the soil food web in your garden, but it can also host numerous colonies of random fungi and bacteria, which can be detrimental in container gardening. Many of these microorganisms specialize in decomposing deceased plant matter, but when deprived of sustenance, they may find ways to attack live plant tissues.
A notable example is the group of fungi responsible for the “damping off” disease, which often lurks in compost. In open soil with various microorganisms, they generally stick to decomposing plant matter. However, when introduced into a flat of tomatoes with limited appropriate food sources or competition, they may target tender new roots and stems to survive.
Numerous studies have demonstrated that pasteurization, involving the heating of compost or soil to temperatures of 160 degrees for an hour or 180 degrees for 30 minutes, effectively eliminates a significant percentage of both fungi and bacteria, including both beneficial and harmful species. Importantly, it preserves the material’s biological integrity and its capacity to suppress other diseases.
Pasteurization also eradicates persistent pests like fungus gnats, while leaving only a few heat-resistant weed seeds behind. It’s vital to avoid temperatures exceeding 190 degrees, as this can lead to the formation of compounds that inhibit plant growth.
During the summer, a homemade solar cooker, crafted from a cardboard box, can efficiently heat a 3-gallon black plastic pot filled with soil enclosed in a plastic bag in just a few hours. In other seasons, you can utilize your oven and a large heat-retaining Pyrex baking dish (which can often be found at thrift stores) to pasteurize compost or soil. When executed correctly, you should notice a pleasant earthy aroma during the process, dispelling any exaggerated concerns about foul odors associated with oven pasteurization.
Here’s what you need to do:
1. Begin by preheating your oven to 200 degrees Fahrenheit. Take 3 to 4 quarts of well-screened, mature compost (or finely screened nutrient-rich garden soil) and combine it with enough water to achieve a slightly moist consistency.
Next, spread this moistened material evenly in a spacious metal or glass pan, ensuring not to compress it tightly to allow steam circulation through crevices. Seal the pan tightly with aluminum foil, and insert a meat or oven thermometer diagonally through the center of the foil cover.
2. Carefully place the pan inside the preheated oven and regularly monitor the temperature at 15-minute intervals. When the thermometer reaches 150 degrees Fahrenheit, turn off the oven. Keep in mind that compost heats up rapidly, while denser soil may take up to 30 minutes to reach the desired temperature.
After turning off the oven, the temperature should naturally rise to around 170 degrees Fahrenheit; if it approaches 180 degrees, it’s advisable to vent the oven. If you detect strong odors, it indicates that the material has overheated.
Leave the pan in the warm oven for a minimum of 30 minutes. For convenience, you can wrap the pan securely in dry towels, although this step is optional. It helps maintain a slower cooling process, resulting in more thorough pasteurization.
3. Once the pan has cooled down, transfer the pasteurized compost or soil into a clean container with a lid. Keep it stored until you’re ready to use it. Pasteurized mixtures are especially beneficial for germinating seeds, nurturing young seedlings, and propagating plants from stem cuttings. Additionally, they offer advantages for long-term houseplants and trees that are infrequently repotted.
However, it’s important to note that you don’t necessarily need to heat-treat compost-soil blends for potting up plants that are nearly ready for outdoor growth. In fact, transitioning to an unpasteurized, bioactive soil mixture during the final “potting up” before transplanting can help reduce transplant shock and ensure a seamless transition into their permanent environment, maintaining uninterrupted growth.
A multitude of ingredients can be harnessed to create organic potting mixes, providing a range of benefits for plant growth. Here’s a revised version of the provided text, with added examples of ingredients:
Bone Meal: Bone meal, prized for its phosphorus content, is a crucial ingredient in organic potting mixes. It stimulates robust root development and flowering.
Kelp Meal: Abundant in micronutrients and growth-regulating hormones, kelp meal enhances plant vitality and overall health.
Greensand: Sourced from marine deposits, greensand serves as a slow-release potassium and micronutrient provider, elevating overall plant nutrition.
Rock-Based Minerals: Various rock-derived minerals like granite dust, volcanic rock dust, and azomite are valuable for supplying essential trace minerals to the mix.
Compost: High-quality compost is a staple in organic potting mixes, enriching them with organic matter, improved moisture retention, and enhanced nutrient accessibility.
Leaf Mold: Leaf mold, as previously mentioned, remains an excellent choice, teeming with organic matter that enhances soil structure and moisture retention.
Rotted Manure: Whether it’s composted or aged, manure from livestock such as cows, horses, or chickens enriches the mix with organic matter, nutrients, and beneficial microorganisms.
Wood Ashes: In moderation, wood ashes can be incorporated to provide potassium and adjust soil pH if it’s excessively acidic.
Coconut Coir: Derived from coconut husks, coconut coir offers sustainability while enhancing moisture retention and aeration in the mix.
Vermicompost: The nutrient-rich compost produced by earthworms, known as vermicompost, contributes essential nutrients and beneficial microorganisms.
Perlite: When added judiciously, perlite, a volcanic mineral, improves aeration and drainage in potting mixes.
Sphagnum Peat Moss: While not the most sustainable choice, sphagnum peat moss can still be used sparingly to improve moisture retention.
Pumice: Similar to perlite, pumice is a lightweight volcanic material that enhances aeration in the mix.
Rice Hulls: Rice hulls, an organic option, facilitate better drainage in potting soil.
Worm Castings: The nutrient-rich waste generated by earthworms provides a boost of nutrients and beneficial microbes.
Alfalfa Meal: Rich in nitrogen and other essential nutrients, alfalfa meal stimulates plant growth and augments soil structure.
Fish Meal: A valuable source of nitrogen and nutrients, fish meal contributes significantly to overall plant health.
Gypsum: Gypsum can be introduced to enhance soil structure and alleviate heavy clay soils.
Azadirachtin (Neem Cake): Derived from neem trees, neem cake acts as a natural pest deterrent and offers some nutrient value.
Mycorrhizal Fungi: These beneficial fungi create symbiotic relationships with plant roots, facilitating improved nutrient absorption and overall plant well-being.
By experimenting with these diverse ingredients, gardeners can tailor their potting mixes to meet the specific requirements of their plants and the unique conditions of their local soil.
Crafting organic potting mixes offers gardeners a wealth of possibilities to nurture healthy and thriving plants. By harnessing a diverse array of ingredients such as bone meal, kelp meal, green sand, and a host of other natural components, we can create tailored blends that suit the specific needs of our green companions. These mixes not only provide essential nutrients but also enhance soil structure, moisture retention, and overall plant vitality.
Furthermore, the process of pasteurization, as described, ensures that our potting mixes are free from harmful pathogens while preserving their organic integrity. This meticulous approach to potting mix preparation underscores our commitment to promoting plant health and success in our gardens.
In the journey towards self-sufficient and eco-friendly gardening practices, it’s vital to explore and experiment with these organic ingredients, incorporating them judiciously to strike the perfect balance for our unique growing environments. By doing so, we not only cultivate thriving plants but also contribute to the sustainability of our gardens and the well-being of our planet. Happy gardening!