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The first use of the term “super-soil” is attributed to a grower in the US, Subcool, who produced a cannabis substrate recipe which he claimed to be relatively fool-proof in producing good yields of fine bud with very little effort and with no supplementary feeding.
“Living soil” was popularised by another grower, the Rev, who developed a growing system and wrote a book called “True Living Organics”. A feature of his system is that ingredients should be “hot-composted” together to break them down into plant-usable form. This also infuses the resultant soil with the right organisms to promote a living soil-web and superior plant growth.
So, while there is a lot of overlap, the two terms do not necessarily mean the same thing.
A “super-soil” is one which claims to provide the correct nutrients, aeration and water retention for plant growth. The focus of a “living soil” is to feed the soil rather than the plants and provide optimum conditions supporting the intricate relationships between plants and soil micro-organisms, for a completely natural product.
It is important to bare in mind that the vast majority of “super-soils” (including Subcool’s mix and commercial potting mixes) in fact contain no actual soil, at all, but rather combinations of compost, peat, coco coir, perlite and various other additives.
Producers of these “soilless super-soils” are confident that their substrates will support the same or similar micro-organisms as a natural soil.
There is an increasing number of cannabis mixes commercially available in SA but a lot of growers prefer to mix their own. Soil-less mixes are very convenient as many growers would prefer not to go hunting down good natural soils to incorporate into their mix or may not have access to them. We will go the same route as Subcool and have a look at what is required to produce a top-class, soil-less “super-soil”.
Green plant material contains nitrogen in various forms, including in chlorophyl and amino acid proteins. The micro-organisms which break these down are responsible for the increased heat of the compost pile as it goes through mesophilic and thermophilic stages. Animal manures are rich in nitrogen in the form of urea and ammonia and the breakdown of these too in a composting process increases the heat. Dry vegetative matter is mostly relatively unreactive carbon and maintaining the correct proportion of carbon to nitrogen, and air and moisture, in the compost pile keeps the processes and heat at the right level. Done correctly, proper hot composting reduces composting time from months to weeks and composting all your ingredients together can produce an excellent substrate. Unfortunately, it is still time consuming and can be very tricky to get exactly right and ensure that all the components are properly broken down.
In our mix we are going to avoid this process by using pre-composted ingredients, together with additives which don’t require composting. We will therefore avoid any “green” vegetative matter or other unprocessed forms of nitrogen. Any super-soil recipe which does not follow a full composting process but says you should leave the mix for a week or two to ensure it doesn’t heat up, is not properly formulated. There should be no unprocessed nitrogen sources or anything else in the mix which can cause heat build-up. If there is then it generally needs to be properly broken down first anyway or it has little benefit to your plants in the short term.
We need to add two important ingredients to our mix which cater for potential problems with container gardening.
- Vermicompost (worm castings) is the king of composts and it is almost impossible to over-emphasise its importance. It is the single ingredient most likely to turn an inert mix into a living, vibrant substrate. The numerous beneficial organisms found in the worm-casts have the ability to inoculate your entire mix under the right circumstances. The fresher the casts, the higher the microbial content. Start your own worm farm, find a friend who has one, or locate a commercial wormery in your area that can supply you with fresh castings. This is the key to growing high quality cannabis and vermicompost is an important component of every effective commercial cannabis medium or recipe.
- Good quality standard compost which has been put through a proper composting process also has significant microbial life, nutrients and humic substances.
- Well composted manures are rich in essential organic nutrients. Urea and ammonia have been broken down by bacteria into more plant-accessible nitrogen and there is no danger of your mix becoming “hot”. As well as providing nutrients, composted manures create a highly conducive soil environment for beneficial organisms.
In some areas where horses are kept, stable sweepings are collected and turned into large hot-compost piles by commercial producers. The end result is an excellent and nutrient rich compost. If you have access to this option, it is best considered as a 50/50 compost/manure combination and treated accordingly.
- Mycorrhizae – Very important, but not as a general soil additive. Most effectively applied by dusting spores on the root ball of cuttings and seedlings at transplant or applied directly where seeds are planted.
- Peat (Sphagnum moss) – Does much the same job as coco coir. It is more routinely used in US and European mixes because it is cheaper and more common there than coco. There are no peat bogs in SA and coco is relatively inexpensive here. Unlike coco, peat is not a renewable resource.
- Steamed bone meal – We are not really in favour of using abattoir by-products. Bone meal is a good source of phosphate but it is slow release and there are better options.
- Blood meal – Avoid! Again, the abattoir and potential pathogen problem. In addition, blood meal is added for its nitrogen content but it has not been broken down and may cause heat build-up under certain conditions.
- Bloom bat guano – 😊 Well of course Subcool could not have been more correct with this one! Phosphate rich bat guano is one of the most universally agreed super-soil ingredients and the perfect source of organic phosphate. The guano breaks down rapidly, stimulating mycorrhizae and other beneficial organisms. This easily available phosphate is extremely important to drive early root production in the first few weeks, after your new babies go into their pots.
- Rock phosphate – Another slow-release source of phosphate. Unless it is finely crushed (micronised), it is unlikely to provide much benefit in the short term. We prefer high phosphate guano followed up by top dressings but micronised rock phosphate is not a bad option as a slow-release backup. Use sedimentary or “soft” rock phosphate (Langfos) as igneous rock phosphate often contains heavy metals.
- Epsom salts – Avoid! Usually added for magnesium and generally mistaken to be organic because your grandmother probably had some in her bathroom cupboard. It isn’t organic, it is magnesium sulphate, a salt of magnesium and sulphuric acid. It is completely water soluble and will leach out of your soil after one or two waterings. (And pollute the groundwater somewhere.)
- Dolomitic lime (Sweet lime) – Crushed dolomitic rock. Calcium magnesium carbonate. A far better source of both magnesium and calcium and we think that no good cannabis medium should be without it. Also buffers against excess acidity and compensates for the tendency of coco coir to absorb calcium and magnesium.
- Azomite (and other quality agricultural rock dusts) – Probably not strictly necessary in a true soil which should have a decent range of essential elements but in a soil-less mix it becomes very important. Plants and soil organisms have evolved to take up the mineral nutrients in the weathered rock particles in a natural soil. The fertility of soils is often determined by the mineral content of the surrounding rocks which have eroded over time. In a soil-less mix these minerals may be lacking. Grinding the rock dust finely increases the availability of minerals such as silica and iron which are important for robust plant health.
- Humic acid (powder or granules) – Humic acid improves water retention and soil quality in poor soils. It is arguably superfluous in a high-quality soil with good humic content, but adding it provides insurance and a good carbon source for beneficial organisms.
- Kelp meal – Kelp is low in nitrogen and, when dry, poses no threat of heat problems in your soil. It is also good as a hot-composting ingredient and will slowly release potassium and trace elements and improve water retention.
- Alfalfa (lucerne) meal – Rich in protein and nitrogen, even when dry, un-composted alfalfa carries some risk of creating problematic hot spots if it has not been composted, so we don’t want it in our mix. It also contains the natural growth hormone triacontanol and makes an easy and excellent tea used as a foliar spray or soil drench, so rather use it for that.
- Feather meal – A bit gross and a slow-release nitrogen source if properly composted. Pointless.
- Fish-bone meal – Optional. Probably less offensive than cattle-bone meal and also provides phosphate but very difficult to get hold of in SA. Go with guano …
- Fish meal – A by-product of the fishing industry, it needs to be properly composted with other ingredients first so it is no good for our mix. Generally used as a slow-release form of nitrogen but will provide nitrogen even when you don’t want it. (We like to drop available nitrogen to cannabis in flower.) Fish emulsion comes from the same source and gives you more control as a supplementary nitrogen feed.
- Crushed oyster shell – Optional. Very slow-release form of calcium. There really doesn’t seem much point? Dolomitic lime is a better option.
- Calcite and gypsum – Optional. Calcite (agricultural lime) is mostly calcium and has very little magnesium content. Gypsum contains calcium and sulphur. They are often used in conjunction with dolomitic lime because some growers believe a higher proportion of calcium to magnesium is needed. This is not an issue when guano is being used as it is rich in calcium and raises the total calcium/magnesium ratio.
- Diatomaceous earth – Increases water retention and provides a good source of silica. In our mix the coco coir provides the water retention and the rock dust the silica, so we don’t really need it. It is claimed to deter soft bodied pests because of its sharp microscopic shards, but only when dry, so it is unlikely to do so in a damp soil.
- Malted barley is rich in enzymes that can break down proteins, cellulose and starches. The science does not strongly support significant benefit to a soil as the enzymes operate only under very specific conditions and temperatures. It could well have some benefit in a compost pile where the heat may activate the enzymes, but not in our mix. (If you are doing your own composting you could give it a try. Get a very pale crushed malt from a homebrew store. Darker roasted malts have fewer active enzymes.)
- Bokashi bran is inoculated with various lactobacillus bacteria strains which break down kitchen waste by a process of lactic fermentation. (Similar to making sauerkraut, Korean kimchi or kombucha.) The fermented kitchen waste can then be broken down further very easily in the soil or compost heap. Some Bokashi bran manufacturers recommend adding inoculated bran directly to your growing medium before planting and claim excellent results. There has not been any significant research done to establish whether or how supplying extra lactobacillus like this would have any positive effect, particularly if your medium already has a strong complement of beneficial organisms, but there are a fair amount of positive reports and it may be worth trying… (Lactobacillus bacteria are extremely common in nature. They are found naturally in soil and in the digestive tracts of many animals, including humans and earthworms, so it is certainly possible that the bran is beneficial.)
Of the 50% total composts, around 20% should be vermicompost, 10% composted manure and the remaining 20% a combination of normal compost and fine potting mix. (If the texture is coarse use more potting mix, if very fine use more normal compost.) Combining different manures will give a broader nutrient profile. If using compost from horse-stable sweepings use 20%. Of this 10% can be regarded as manure and 10% as compost so another 10% light potting mix will complete the equation.
We sometimes add a little coarse river sand in addition to perlite or as a partial replacement. It does not provide as much aeration as perlite, but it does prevent compaction, improves drainage and adds weight and structure to the mix. This can be useful if you intend growing large plants in light plastic pots or grow bags which can topple over easily under the weight of the plants when the medium is fairly dry.
To the above we must add the non-negotiable additives: Rock dust at around 3-4 mls per litre of mix, dolomitic lime at around 5-6 mls per litre and high phosphate bat guano at 15 mls per litre. The composted ingredients provide good levels of nitrogen and potassium, and the additives provide the phosphate, calcium, magnesium and trace minerals for powerful growth.
Optional additives if you really want to go the extra mile are humic acid powder or granules at 0,5 mls per litre, kelp meal at 10-15mls per litre, and micronised rock phosphate at 3-4 mls per litre.
The easiest way to do the mix is to work out how many litres of soil you need in total, divide it by ten and get a container that size to measure. So, for example, if you want 50 litres of mix, use a 5-litre container. One container is 10% of the total mix, so you can easily measure each of your main ingredients. (2 vermicompost, I composted manure, 2 compost/potting mix, 2,5 coco coir and 2,5 perlite; or variations on this.)
Don’t forget to thoroughly rinse your coco coir. For the additives just multiply the recommended amount per litre by 50 litres (or whatever your total is) and measure it out. Mix everything well and wet thoroughly but without excess run-off. Use immediately or wait a day or two for the biological processes to kick in.
To this inoculant category we could add bokashi bran which will provide supplementary lactobacillus, as discussed above. Do a comparison by adding the bran to one pot and not another and see what the difference is. The recommended dosage is ½ a cup of bokashi bran to one cubic foot of substrate. (This works out to roughly 5mls of bran per litre).
- Most modern cannabis strains are heavy feeders and unless you have an extremely large plant container, there is very little prospect that it will hold enough nutrients to sustain your plant at optimum grow levels throughout its life.
- In any event, generally during the vegetative cycle we want to feed more nitrogen and then drop it back during flower but maintain phosphate and potassium. The best way to do this is by using different supplementary feeds.
For now, we hope that you find the above information useful and that it gets you off to a good start. We have not gone overboard on additives, some of which add little or nothing to the equation. By following the above simple guidelines you can produce a cannabis growing substrate comparable with commercial products. You can also make subtle changes to your own mix to accommodate your growing style and environment. If you are using large containers and automated watering, you may want a little more perlite and to feed more frequently.
Conversely, if you are growing in smaller pots in a very dry environment, you may find that more coco for hydration is needed. See what works for you and develop from there.