Topsoil in the mix.

Some people expressed an interest in a thread about using topsoil as part of an organic soil mix so here we go.

First off - Here are what I see as the potential advantages and disadvantages of topsoil.

Advantages –
1. soil is what most plants have evolved to grow in. We refer to our medium as soil but mostly it has no ‘real soil’ content
2. Good micronutrient content. Soil is the ultimate in aged rock dust!
3. Potential to impart flavour – i know from my own experience that vegetables grown with soil in the potting mix have better flavour than those grown in only peat/compost.
4. Holds water well and no re-wetting problems

Disadvantages.
1. Heavy – may become compacted
2. Risk of introducing harmful pests/diseases. Jorge Cervantes recommends not to use soil dug up from the garden/field.(more about this later).
3. May hold too much water.
4. Quality will vary.

At present I use a good quality bagged topsoil as about 20-30% of my mix with great results. I have yet to do any side by side comparisons but I’m very happy with the taste, aroma, high and yield of my plants. (check my grow diary for pics. All of the plants shown were grown in a mix pretty much like this.)

3 parts peat
2 parts topsoil
3 parts perlite
1 part mushroom compost
1 part wormcasts
2 parts coco (optional - to keep open structure preferred by sativas)

dolomite lime 5g/litre
N guano - 5g/litre
P guano - 10g/litre (5g/litre for veg)
Rock phosphate 5g/l
rock potash 5g/l
seaweed meal 5g/l

Bagged soil
Topsoil from the garden centre is likely to have been sterilised/solarised so may be a safer bet than garden/field soil. Having said this I have seen some shite topsoil from a bag so I prefer to check the quality before I buy it. Look for a bag that has already split and get a handful. You are looking for a nice dark tilth with good crumb structure (not dusty). If you squeeze damp soil into a lump it should stick together and feel slightly spongy - and when the lump is pressed gently it should easily break back up into tilth again. It is also worth pointing out that even the same brand of topsoil (and compost for that matter) will vary from place to place as the source will vary. Always best to check.

Garden / field soil.
I would also like to take this further and try good quality garden soil. Again It helps to have experience of what good soil is. If you want to try this you should research solarisation (leaving to cook in the sun to kill pests/diseases) or some form a gentle sterilisation. I would also recommend sieving and keeping a look out for any larvae/cutworms that could give you real problems. Certain plants/weeds can tell you something about the native soil – nettles for instance are a good indicator of fertility.

I am planning to try some clay soil as well – clay can get very wet and soggy but a well cultivated clay soil is amongst the most complete in terms of fertility.- the small partical size in clay (whilst it has it's disadvantages) gives a huge surface area - some clay can have a surface area equivalent to the size of a football pitch in every gram! - this surface area has a major influence on the soil's ability to hold onto nutrients rather than them leach out. Moreover, clay particles are pretty unique to soil in being negatively charged - which makes the all important ion exchange much greater.

hopefully we can expand on this

V.

i like your soil mix V, i also use WC and mushroom compost. i havent used topsoil in my grows but i have used potting soil from a nursery as an addition to my regular medium and have had positive results ! i take it that you amend the topsoil into the medium at certain points in growth?

i also am in the favor of soil from outside vs. soilless, the soil in your backyard may not be perfect ( in some places it may be real close to perfect). but given a little time, love and care. it will outshine anything in a bag.

oldbootz said:

i like your soil mix V, i also use WC and mushroom compost. i havent used topsoil in my grows but i have used potting soil from a nursery as an addition to my regular medium and have had positive results ! i take it that you amend the topsoil into the medium at certain points in growth?

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well verdant, as much as I am theoretically for it, my WC is not set up for composting.

Thats a big yes on the garden soil in the container mix. I've been adding more lately. Lots of friendly critters in there. I think the plants are happier.

oldbootz - i just add the topsoil when i mix the soil. i use the same basic mix posted above but change the ferts a bit for veg or seeds.

Mr G - thanks for weighing in on this. if a grower with your experience is using garden soil then i feel better about experimenting a bit more.

V.

Hey Verdant

I'll post back when I've gathered up some of that red soil for an "impart flavor" test. Need to grab some litmus paper also, no idea what this red soil even is? Good time to test the runoff from the red Pumice rock I can get for dirt cheap too.

One thing for sure, it'll be red

we have red clay here.

to find out a general idea what your soil is......get a jar, fill 1/3 the way with your soil, fill with water, put lid on, shake like mad, let it settle fully and post a picture of the results here.

ooh its a like a palm reading ! hehe can i have one too !

(scrounges around for a glass jar)

If the jar breaks, it means you have rocky soil.

chef - that would be great! - i have limited space for side by side tests
as i think you said somewhere else, red usually indicates iron, and with acid/alkali loving plants it really boils down to whether they like iron or not.
so if you keep the pH in the right place you can control the availability of the iron. what % of it are you going to use in the mix?

Jaykush - cool - the jar test
if any of that clay soil has been properly cultivated into a crumbly soil it might be good to try some sometime. leaving a few clods of it out over winter lets the frost break it up as i'm sure you know.

bootz - i bet all your jars are full of weed

h.h. LOL!

V.

I'll dig out some of that red dirt today & snap a pic of the sedimentary layer, it hasn't seen light in a couple million years. No idea what it is or how much to use at this point? Wait & see what it smells like I guess? strong, weak, metallic?

Broken jar lol still a great idea jaykush

if any of that clay soil has been properly cultivated into a crumbly soil it might be good to try some sometime.

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clay soil turns into fantastic garden soil given a little love. clay is naturally high in nutrients compared to other soils.

chef....no jars...what kind of stoner are you. the jar test is worth it if you are going the topsoil route imo. it tells you SOOO much.

chef - i would try 20-30% .enough to make a difference but you do need some of the regular stuff to balance it out - depends on how much water it holds.

jaykush said:

clay soil turns into fantastic garden soil given a little love. clay is naturally high in nutrients compared to other soils.

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it does indeed!- my house was built in the thirties and the clay has been worked for most of that time - it's great as long as you dont try and dig it when its too wet or dry. if you dig along the fenceline the original clay is yellow and you could make pots out of it.

Hey VerdantGreen! Thanks for the post. I just bought a couple bags of topsoil because it was very cheap and the only other option was Miracle Grow with that time release shit in it.

I don't have any peat moss. I have some vermiculite though. Do you think that would be ok to substitute?

My plants are in 100% FoxFarm Ocean Forest right now, but I couldn't shell out the $25 my local shop wanted for another bag. So do you think this mix would do alright with the vermiculite instead?

hi bendo. i personally dont think vermiculite would be very good as it holds water and topsoil can get pretty wet on its own (depends on the soil) a bit of vermiculite wont hurt - but not as your drainage ingredient.

i would try and amend it with perlite or some substitute for that like sharp sand (for drainage). coco or peat would be good too (to lighten the mix).

also remember that you will need some nutrition for the plants too. check the organics for beginners thread for more ideas.

it can be a pain in the ass but the one thing i wouldnt cut corners on is your soil. great that you want to mix your own but you need at least the 3 basic ingredients imo.
soil + peat/coco + perlite or similar. peat and sand are also dirt cheep if you are trying to save money.

remember some dolomite lime or oystershells too!

V.

peat/coco/ OR COMPOST!!!!!

Hey V

Sorry it took me a minute to respond. I don't have too much to add. However, I like your research and presentation a lot. One concern I have you already pointed out: the bulk density of loam, and that it can hold a lot of water (thus less air). The % air porosity of loam is low, for cannabis we want the % air porosity of the soilliss mix to be ideally 20-40%.

To my understanding, if the loam is not mixed with some type of clay it could aggregate poorly. Zeolite might work, or other clays, Piedmont red clay is a good example of a good type of clay to mix with loam. Which also increases the CEC (Cation Exchange Capacity).

All in all, I don't see a reason too add loam in the first place. Compost or vermicast would be much superior IMO.

To Jays point about clay, it can be important to use clay-loam, not just loam, and not just clay. The loam assists in aggregateing the clay particles. I learned that from the Luebke family. Clay-loam is an important part of "Controlled Microbial Composting" (CMC) so the clay can help in forming the "clay-humus crumb" which increases the amount of humus. Also the clay acts as a negative ion (cation) magnet by virtue of its sadly poor CEC (20-30 meq/100 g). Zeolite's CEC is in the hundreds of meq/100g.

I am interested to see what comes of your testing. Good work so far

HTH

One thing I was just wondering about:
Where does all the topsoil/loam come from? It seems like 'harvesting' topsoil would be akin to clear cutting. Or are there loam farms who alternate fields they harvest from?

I'm gonna do some reading, I am pretty curious now. If anyone knows that would save me some time, thanks.

GD just curious. when you give all these ratios and percentages. is this for controlled indoor growing, or outdoor or both? controlled greenhouse?