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Coco vs. Soil vs. Potting Soil
It can certainly be overwhelming to know which medium is best to grow your high value crops in. Any good media option will help give your plants, or properly set them up to obtain water, oxygen, and nutrients. Three of the more common media options to grow your high value crops in are soil, soilless mixes (Potting soils) and coco, sometimes labeled as “Coir“. Each medium has its advantages and disadvantages.
In some instances, the decision will be made for you. If you can only grow outside in the ground, then you will likely be growing in soil. If you can only grow inside in some containers, you are probably looking at using a soilless potting mix. If you are growing hydroponically, then you may be using bricks of coir. However, there are instances where these materials may be blended or where you can grow in coco outside or in containers, where you might use soil in your pots, or where you may choose to incorporate soilless mixes into your outdoor grow.
Your growing area, objectives, resources, and strain will dictate which medium will likely work out best for you. There is not always one medium which will work best in all situations. Trial and error, personal preference and experience will likely play as much of a role in your decision about which medium to use as any other single factor.
Before deciding, let’s take a look at some of the differences between the media options as well as some of their pros and cons.
Benefits and Considerations of and for Each Medium
Soil is the most ubiquitous medium for growing plants in. For the majority of mankind’s endeavor to grow all types of flora, it has been the default substance. It is found all over the planet. Like any of the media we are looking at, there are pros and cons to growing in soil.
There is not just one type of “soil”. There are thousands of types of naturally occurring soils and in all micro-regions the soil will consist of whatever organic and inorganic materials have either decomposed or been deposited over millennia. Quality soils that can support plant life however will all have similar characteristics which can be supplied by a variety of inputs and sources. So long as they are of appropriate texture, can retain water and nutrients, and are able to efficiently drain, they have what it takes as the basis to support quality plants. An easy way to test if your soil has these qualities is to give it the “squeeze” test.
Moisten the soil well before testing it. Then, grab a small handful of it and form a ball. Squeeze this ball of soil between your thumb and forefinger. Soils with good structure will form a “ribbon” when you squeeze it. It will stay intact when squeezed but not hold its ball shape. If water is released then it likely holds too much moisture. If it breaks up when squeezed or retains its shape too well, it may need to be amended. Good soils are like “Goldilocks”. They are not too wet, not too dry, not too loose, and not too firm.
Outdoor soils tend to be “alive”. They support millions of microscopic organisms that help plants to grow. For that reason, some soils do not need to be amended, but naturally contain enough nutrients and micronutrients to provide your plants with everything that they need. There are many other benefits to growing your plants in soil.
Growing outside in soil is the most inexpensive method of growing plants. There are no containers to purchase, grow lights to setup, and no costs associated with disinfecting your grow space before or between crops. As such, it is often regarded as the “easiest” method of growing and the most accessible for newer and hobbyist growers. Soil is also the most forgiving of the mediums. Fine tuning pH and nutrient levels are not as critical in soil-grown crops versus those grown in artificial media and grown indoors. High value crops grown in soil tend to have more pungent smelling and complex buds, owing to the higher terpene levels that soil-grown plants tend to have. Growing in soil does have several drawbacks though.
Plants grown in soil usually grow slower than those grown in coir or soilless mixes. Yields also tend to be lower in soil than in soilless mixes or coir. Worse than that though is that soils can contain harmful bacteria as well as pests that can be harmful to your crops. Growers who are adept at growing in coir or soilless mediums will need to adjust their watering schemes and schedules when growing in soil. Soil-grown plants often need more water than plants grown in soilless media.
It is advisable to have soil tested by a lab prior to growing crops in it. This way, you will know what nutrients are already present and in what quantity. You will also learn how much organic material is in the soil and what is the capacity for both holding onto and for releasing nutrients to your plants.
Soilless Mediums (Potting Mixes)
Soilless potting mixes come in a wide variety of blends. As the name implies, the only thing they will not have in them, is “soil”. A good soilless mix will retain enough moisture for the plants that they are supporting, but not so much that it does not drain well. They will be sterile so that they do not transport any diseases or weed seeds. They will be slightly acidic (6.5-6.8), and they will be low in salinity. Soilless mixes are a blend of primarily organic materials, though they can have inorganic materials like sand or lime in them. Each particular soilless mix blend will contain various ratios of perlite, vermiculite, peat moss, sand, compost, rockwool, mulch, and even coco coir.
Perlite is a small white pellet-like material that is sterile and adds not nutrients to the mix but helps air flow within the mix and around the plants’ root systems. Vermiculite can also help with the aeration but is great for helping the mix to hold on to water. It is sterile but can provide some magnesium and calcium to the mix. Peat moss has a very high capacity to hold onto moisture, but it has a very low pH and too much will make the mix too acidic if not counteracted by enough lime to raise the pH. Sand also helps with aeration, but its primary purpose is to add weight to the mix. Soilless mix is very light and can at times be too light causing container grown plants to be easily knocked or blown over; sand helps mitigate this issue. Compost is often added to soilless mixes because of the nutrient punch it packs. It needs to be properly aged though before using so that it has a proper carbon to nitrogen ratio, and it must be low in salts so as to not interfere with plant germination and early development.
The various ingredients and respective ratios vary from proprietary blends to those that are created specifically for germinating, water retention, or for replanting mature plants and dozens to hundreds of other specialty blends for specific crops or specific environments. They may be certified organic, aged, sterilized, or subjected to other treatments. The bottom line is that there are literally hundreds to choose from.
For any grower who is not growing hydroponically, and is growing inside, soilless mixes are a good way to go. Growers who grow in containers and wish to grow outside may choose soilless mixes as well. Most plants can adapt to and even flourish in soilless mixes. Most mixes are lighter than field soil and as such often allow more air and water to flow around the root systems of your plants.
Some of the other advantages include lesser instances of pests compared to field soils, and less likelihood to overwater your plants. Since soilless mixes are lighter, containers filled with them are much easier to carry around than if they were filled with traditional field soil. One of the down sides of soilless mixes though, is that when planting any larger quantity of crops, the costs of some soilless mixes can add up quickly. You may also find yourself having to give plants grown in soilless mixes more nutrients than those grown in soil or coco coir which can increase the costs as well.
Fortunately, there is a range of price points out there for potting mixes and it is likely that you can find one that will fit your purpose as well as your budget. In some cases, soilless mixes can be reused. This practice should be evaluated carefully though to make sure that there is no transfer of diseases or pests. Only reuse soilless mixes that were in contact with healthy plants. Only reuse mixes where you can be sure of all of the ingredients and inputs as well. “Used” soilless mixes should be sifted to remove old crop and root debris and when possible, they should be thoroughly rinsed out to leach out any excess nutrients.
Coco coir, alternatively referred to solely as “coir”, or “coco”, is a medium created by using the fibers from the coconut husk. Some growers mix it into their soilless blends while others grow in straight coir. Coco coir is naturally neutral, so it is like a blank slate unto which you can input the pH or EC levels that you want. There are a lot of other benefits to growing in strait coir as well.
Coir is one of the easiest mediums to use. Also, plants tend to grow faster and larger in coir than in soil. This is partly due to the good drainage that coco has. Concurrently, coir is highly absorbent as well. This means that it will suck up all the water you give it but will not hold an excessive amount that will drown your plants. Its good drainage also supports good aeration which will allow for adequate air flow around your root systems. This in turn encourages your plants to develop a robust and healthy root system.
Coir naturally has anti-pathogen properties. This translates to mean that pests and diseases have a difficult time entering your plants’ roots when they are growing in coir. One of the best reasons to use coir, though. unlike peat moss, is that coco coir is a renewable resource. It is a by-product of coconut harvesting, which are of course grown year after year. Like anything though, coir is not perfect. It does have the benefit of being able to be reused for successive crops, but there are some downsides and disadvantages to using it as well.
Some growers find coco coir to be very challenging to use. It can be difficult to find the right nutrients to use. It is advisable to use fertilizers that are designed for use with coir until you are familiar with its properties and are comfortable using it. Coir can act like a wick and draw up nutrients away from the root zone. This means that even if an appropriate amount of nutrient solution was added, your plants may not be getting those nutrients. There are situations when coir will block access of nutrients to your plants. Those nutrients are usually magnesium, calcium, and iron. Some of these issues can be addressed simply by soaking the coir first with a nutrient solution prior to using it. Coir may also be treated chemically during the drying process. It should be rinsed off with distilled, deionized or RO water before using. This rinsing is also known as “buffering”, but buffering is more than just rinsing with water.
Coir, like all organic matter is covered with negatively charged ions. These ions, attract cations, which are positively charged ions. You may have heard of the cation exchange capacity, or CEC. This is a measure of how many nutrients a medium can hold before they are leached out. The CEC of coco coir, if un-buffered can tend to be too high in sodium (Na) and potassium (K) and too low in Calcium (Ca) and Magnesium (Mg). Too much K will result in too little Mg being available for your crops. Too much Na can be toxic to your crops, especially to young and bare root plants. Coco coir naturally can have too high a level of salts because coconut trees often have a very high level of salts. They often grow along coasts and absorb salt from the water that they grow by.
Some commercially available coco coir is already buffered when you obtain it. The manufacturers soak it in a solution of calcium, sometimes mixed with magnesium before it is packaged and sent out for distribution. The pH, CEC, as well as any salt content should be disclosed on the packaging materials or available on the manufacturer’s website with the product info. These numbers will indicate whether or not the coco coir you have will need to be buffered still.
You can buffer your coco coir before using by rinsing it with a solution of water, calcium, magnesium, and any other nutrient that you know your crop will need an abundance of. Of course, coco coir does not automatically need to be buffered at all depending on what and how you are using it. If you are using coco coir pots and placing them in soil, the soil itself will buffer the coco. If you are growing in straight coco or even mixing it with another soilless media, then if it is not already buffered, you should do a buffering rinse of it. If you are planning to reuse your coco coir products, it is a good idea to buffer them again prior to reuse.