How To Build The Perfect Soil Mix
For newbies to indoor gardening or anyone who is not the most attentive grower, growing plants in pots full of soil mix is easier and less troublesome than in a hydroponic (no soil) system. Soil mix can hold moisture and nutrients for plants to take up whenever they need it, so they don't need constant watering and fertilizing. And while keeping the pH of the nutrient solution in the recommended range is always important, the range is wider for soil than in hydro and soil is more forgiving when the solution falls slightly out of the range. But let's be clear – we're not talking about "soil," the dirt you dig up outside. The mix used for growing plants in pots actually has no soil in it. That's because ordinary garden soil typically contains clay, which holds so much moisture that plants' roots get soggy, conditions that lead to root rot. Clay-heavy soil is also very dense, preventing the dispersal of nutrients and inhibiting the spread of roots. Soil mix, on the other hand, is loose and drains well so roots don't rot, but the ingredients can soak up and gradually release water and nutrients.
Components for the Perfect Soil Mix
Here are the components of a healthy soil mix for your indoor garden:
- Peat moss: You see peat moss in big bags at garden centers and home stores. It's the dry, fibrous material that results when mosses slowly decompose in bogs. Peat stays loose in soil mix, so it never becomes compacted enough to block root growth, and it holds several times its weight in moisture, which it releases to plants' roots as needed.
- Coir: Made from the fibrous husks of coconut shells, coir is used to make doormats and hanging basket liners. For use in soil mix, the fibers are washed and heat treated, then compressed into blocks or bricks that are soaked to break them up. Coir (pronounced like "core") is naturally organic and sterile, and some studies have found that it actually suppresses the fungi that cause root rot. Like peat, coir holds moisture and nutrients, and it stays loose. Its pH is on the slightly acidic side (about 5.8 to 6.8), but less so than peat (which is about 3.8 to 4.8). Coir is typically more expensive than peat.
- Vermiculite: A mined form of the mineral silica, vermiculite is exposed to very high heat, which expands it into white or gray pellets. The pellets retain moisture and nutrients, gradually dispersing them to plants' roots. They also hold open air pockets in the mix, allowing essential oxygen to reach the roots. Vermiculite doesn't decompose and it is odorless, non-toxic and sterile. Vermiculite has a neutral pH of 7.0.
- Perlite: When volcanic glass is heated to a super-hot 1,600 degrees F, it expands to up to 20 times its original size and opens up countless tiny air pockets to fill the new space. The tiny cells (visible only through a microscope) absorb moisture, which very slowly drains out. Like vermiculite, it is sterile and pH neutral. Moisture evaporates even more slowly from perlite than vermiculite, so it's a better choice for growing plants that need a steady level of humidity.
- Composted bark: Homemade compost can be a valuable component of soil mix, but it can contain weed seeds or, even worse, unwelcome fungi that could harm your crops. Composted bark, on the other hand, contains only one ingredient – decomposed outer layer of pine or other trees. When broken up into minute pieces, it helps maintain air spaces in your soil mix and provides nutrients as it continues to decompose.
- Worm castings: If you buy a bag of indoor garden soil mix, you may see that it contains blue or green beads or pellets. They are synthetic fertilizers that have not been formulated for indoor crops and they are potentially damaging to your plants and the environment. A better option if you want a small dose of nutrients in your soil mix is worm castings, the polite term for the soil-dwellers' excrement. It is rich in nitrogen, an essential nutrient, which is released slowly as plants need it.
The Formula for Soil Mix
To create your own perfect soil mix, thoroughly blend 1 part peat or coir, 1 part perlite or vermiculite, one-half part composted bark, and one-half part worm castings. You can grow just about any crop in your indoor garden with this mix. After each grow cycle, dump the contents of each container and start with a fresh mix.
Going Organic with Garden Soil
Now that you understand the basics of building your garden soil, you may want to take it one step further – by making organic garden soil. Doing so helps you maintain complete control of your plants because you will know what your plants are living in and have even better resistance to pests, disease and fungus.
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