I am a soil recycler myself and thought this was a good read...
soil heresy by the 3LB ~ CW
We are about to commit heresy and tell people that we ALWAYS re-use our soil. No soil has left the garden's of the three_little_birds since before the turn of the millennium! Some growers will tell folks to throw out their soil after every grow, and we've known plenty of commercial growers that happily do that to make sure they do not have pest or nutrient problems. Maybe that even is the best solution for your grow, we can't say for sure, as always your mileage may vary. We are poor simple medical users (and aging hippies, etc.), and spending something like $20 for a bag of FoxFarm soil rubbed us wrong! With our container system it might take 2 full bags of that soil for 3 plants!
Now again . . . someone who is involved in commercial (rather than personal medical) production might not be so inclined to bother with making sure their soils stay healthy and all the work we go through to ensure our soil's health, but for us it is a labor of love and we feel our results speak for themselves.
Anyway, like we said, our soil never leaves our grow, it has all been recycled to the point that we could not even begin to tell you how many times it's been through our system! A good commercial potting mix has always been the base for our soil. We look for a product which is 100% organic, and recommend that you avoid ALL chemical salt ferts like the plague if you value your soil health. This especially includes timed-released chem ferts like osmocote! Depending on what we have found for soil, we go from there. Some cheap organic soil mixes contain little more than peat, pearlite, and dolomite lime. These absolutely need amending to start off. Some organic soil mixes are much more complete and need little or no amending for starters.
Organic mushroom compost is certainly one of the hot soil mediums these days, and we've certainly had great success mixing it in with our soil remixes to add fresh organic matter. We can't however comment on it's longer terms effects in soil remixes. Since we found a cheap source of mushroom compost, we have also been top-dressing our plants with it almost exclusively, so we imagine that we will soon discover if remixing the ‘shroom compost will have any detrimental effects.
Once through it's first grow (the plants fed 100% organic with earth juice, teas, fish ferts, and liquid kelp) our container of soil has it's root balls pulled and it is dumped into a very large rubbermaid container w/ a lid (50 gallon container) These container's are longer than our 2x3 growing containers, so with 2 people lifting and dumping, it's not too hard to keep this step neat. Each bin can actually hold more than the contents from a single grow-container (2 grow-containers of soil will actually fit, but this makes mixing in amendments very difficult and messy.) Now we proceed to give back to our soil mix what our plants have taken (and then some.) We get out our kelp meal, bone meal, blood meal, greensand, rock phosphate, diatomaceous earth, and dolomite lime and get mixing. Depending on the soil's condition this is also where we might add a little more perlite if soil compaction looks to be a potential problem.
Folks are going to ask us how much of these different supplements we add, and the only honest answer we can give is - it depends! If the plants we'd raised previously in that particular container had shown any signs of being short on a major nutrient N–P-K - it's not too hard to throw in an extra cup or two of the appropriate organic supplement (Blood meal / Alfalfa meal for N - Bone meal / rock phosphate for P - kelp meal / greensand for K and other micro nutrients.) A nice full 16 oz plastic cup of each of the prior mentioned ingredients would be our baseline for supplementing this round of soil re-mix. We will generally double this amount if any nutrient shortage has shown. . .
The greensand and rock phosphate are very slow to dissolve and be absorbed by plants, and are not normally used by many indoor container gardeners. Their slow release is what helps to make our system work! They will still be in our soil for the next couple of grows, doing their part for our soil health. This is the point where we would also add some of our own compost (assuming there is some finished and ready - if not some mushroom compost has proven to work.) Our compost is made from the usual standards, household veggie food scraps and such, with the addition of all our used grow scraps. Fan leaf, chopped stems, and the "leftover's" from processing by bubble bag or tumbling are all composted and returned to our soil.
Now we will wet this whole mix down lightly and let it "cook" for a spell. We have three large bins like this for soil remixing and composting. Folks always want us to be specific on amounts and times, and we do a lot of this by feel, so when we say we let the soil cook for a "spell" - how long depends on feel and need! The minimum time our soil sits is two weeks, and it's sat waiting for use for a couple months like this during slower times in our grow. This time gives soil bacteria a chance to work and make the various organic amendments more quickly and easily available for our plants. We use this soil again for another grow, watering with our usual array of teas, Earth Juice, etc. If needed, containers are top-dressed with compost (our own or mushroom compost depending on availability) as any soil settling occurs.
Upon yet another successful harvest, the soil is reconditioned again. Once we reached our third mix of soil, we cut back on the soil amendments. The greensand and rock phosphate are still working from the last re-mix so we don't need to add any more of them for sure. What remains in your soil at this point in terms of nitrogen and such may depend on your strain, some strains are much more greedy for some nutrients. So if our plants haven't shown any signs of yellowing as they mature, we figure there is nitrogen enough in the soil for the next round (at least to get started - we can add more N on the fly with fish ferts and teas if needed) and no blood meal is added. If yellowing has occurred then blood meal is added again. Kelp meal is usually added again since many of the major liquid organic ferts seem a little short on potassium, and also because we like the micro nutrients kelp meal provides to our plants. Dolomite lime will probably be necessary again too, and it's possible your soil will need even more this time than last. Any peat in the soil adds acidity as it decomposes, and the lime balances this as well as providing magnesium. After the standard 15 - 30 days of standing moistened waiting for use this soil is used still another time. Now our soil has grown 4 crops of herbs and is still going and growing strong. At this point, we have started plants in our soil remixes directly alongside plants in fresh potting soil, just to make sure our mix wasn't subtly stunting our plants.
The plants grown in our 4th and 5th generation soil remix did far better than those directly alongside grown in fresh from the bag FoxFarm OceanForest potting soil! Because our garden is a continuous harvest setup, once we are to our 4th or 5th remix, it's starting to get hard to keep track of exactly what soil has been remixed where, since half used bins of remixes are often dumped together to make room for another round of used soil coming from the garden. So we simply continue adding amendments by feel as needed.
This is how the three little birds use soil. We know we break the rule we have all been told to follow - to never reuse soil. Even those "radicals" we have seen reusing soil, have always described letting their soil go out to their veggie gardens or flower beds after 3 or 4 grows. We decided to push the envelope and see how far we could take it . . .
We still haven't found a limit for the number of times we remix our soil, and our harvests and plant vigor keep improving.
Oh, just to add another bit of heresy, you may have noticed our container grows suspended above the floor on wheeled furniture movers. It's a very convenient way to keep the plants in larger containers mobile. . . but you also must realize then (if you think about it) that out grow containers have NO drainage. Our soil mix, which is now has been remixed double digit times, has NEVER been flushed! We warned you all at the start of this post that some might consider it heresy . . . And we can’t even begin to tell you how we can break these rules and get better results than average - but it works for us and we wanted to let folks judge for themselves. (Eds note: 3LB claimed to regularly get above 2g/watt as well as reaching high marks of 4g/watt!, and they posted the photos to back it up. If anyone has any of these photos or posts please add them to this thread or section)
one thing we might add - we certainly would not remix soil from any containers where we'd had a bug or disease problem - even getting bud mold would be enough for us to say - no thanks to a soil remix
we were discussing this among "the birds" the other nite - and one line that a little bird said comes to mind . . . "Farmer's don't strip their topsoil after a harvest - or even a few - in fact their soil is their most precious commodity - why should it be different for indoor gardening as long as proper care is taken to build healthy soil?"
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