An experiment for potting soil

I have been using what a friend got as top soil for a base for my potting soil.  We bring home several buckets at a time and I add what I can from what I have here for potting large tubs of things and even seedlings.   It works ok but is really dense and heavy.

This summer and into the fall I want to try growing some deep rooted annuals that would fill a large soil filled container with masses of fine roots to decompose and make the soil somewhat lighter in texture.

We do similar in our gardens...the difference would be more controled and I hope I could bust up the mass once it breaks down.

Ideas for seeds?
I have wheat...our feed store sells a lot of cover crops by the pound like oats and winter peas?





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I am already doing something like that. When I'm done with a pot, I leave the roots in place and add it to the next batch.
Maybe it's not ideal, since these roots are going to decompose in the same place where the new plant is growing, but it's fast and easy.
If there's ill effects, I am not noticing them.

Abraham Palma wrote:I am already doing something like that. When I'm done with a pot, I leave the roots in place and add it to the next batch.
Maybe it's not ideal, since these roots are going to decompose in the same place where the new plant is growing, but it's fast and easy.
If there's ill effects, I am not noticing them.

Thanks for your input!
And yes, that's what I normally do also.

For this, since I'm starting with fresh soil in large containers I thought I could choose a combination of seeds that might benefit both the texture and fertility more deliberately?

Good idea.
Yes, grains sounds like the best choice. I suppose you can cut them before they go to flower, when the root system is already developed, and not wasting energies in anything else.

I don't have data to use to browse at the moment but seems like I've come across drawings or photos of root structures showing a comparison...thinking 'out loud' now.
I think I need fast growing and deep, fine roots that would fill the available space....a summer legume with a grain ideally that would grow into the fall then die back with the first freeze?

Judith Browning wrote:
I think I need fast growing and deep, fine roots that would fill the available space....a summer legume with a grain ideally that would grow into the fall then die back with the first freeze?

Both Pam Dawling/Sustainable Market Farming and David thd Good/the Survival Gardener recommended sunn hemp in their blogs as the warm season cover crops for both biomass and soil building. It will be frost killed, but before that it can be mowed to control height and promote root growing.

i threw some oats out that i thought were ruined. they grew. after squirrels ate all the harvest, i went back to digging and noticed the oats produced a mat of amazing fine roots. i think oats would be worth checking out for your potting soil experiments.

May, thanks for that suggestion...I've been meaning to ask our feed store if they can order sunn hemp.  Besides my potting soil project I think I'd like it as a cover crop in one of our gardens.

Jonathon, thank you!
I was hoping oats might be a good choice but wasn't sure how deep the roots are.

Toby Hemenway says up to 40% grasses with legumes for cover crops so will see if I can plant a summer bean or pea along with it or the suggested sunn hemp.

We preserve all the rootlets in our our growing pots and tomato barrels. I just plunge a big honking serrated blade into the soil and chew off the small stuff, and yoink out the big stuff.

I'm not sure these rootlets would be enough to keep the soil loose enough for young plants. In our potting pile, there's a lot of leftover perlite. Since it doesn't break down, it's a good thing to reuse it, and it keeps soil from packing.

Well, here goes...
Sifted 3 five gallon buckets of 'top soil' into a heavy rectangular tub with drainage.
Watered and planted organic soy beans (I buy them bulk for tempeh) and organic white winter wheat that I also buy in bulk for bread and sprouts.
I decided just to go with what I already have for the first tub.

When I cut the wheat and beans off short I' m considering adding another layer of soil and planting austrian winter peas and oats....both will grow through the winter so then I need to have a rough idea how long those roots will take to decompose to be useful for potting soil?

I'm going to try the same method in my big planting tubs after lifting moringa and dahlia roots for the winter.

Thoughts?
Length of time for roots to decompose?
I never think about that so much in our gardens where we grow winter cover crops but for potting soil for flats and small pot transplants I'll want it somewhat decomposed but not gone?

My thoughts: monitor temperature carefully. Even if it is cold composting, it still releases heat, and in midsummer it may be excessive.
I had one plant die by root boiling at more than 50ºC.

Are you going to do it as inground cover cropping? i.e. terminate the growth before the plants set seeds and also mix in the tops with soil to break down? If you take away the above ground portion, i am afraid a significant amount of fertility will be lost in that potting soil.

Abraham Palma wrote:My thoughts: monitor temperature carefully. Even if it is cold composting, it still releases heat, and in midsummer it may be excessive.
I had one plant die by root boiling at more than 50ºC.

I only just planted the seeds so no roots yet. I think by the time they are well rooted and I cut the plants back it will be cooler here....I was hoping really fine roots might not release much heat though good to consider.
I know what you mean though as I have some plants in black tubs in too much sun and they are really stressed and some are almost dead.

May Lotito wrote:Are you going to do it as inground cover cropping? i.e. terminate the growth before the plants set seeds and also mix in the tops with soil to break down? If you take away the above ground portion, i am afraid a significant amount of fertility will be lost in that potting soil.

Yes, I thought I could cut back to just below the soil line and possibly add more soil and replant with peas and oats.
I've been so focused on tilth I hadn't thought about adding the 'green' back in for more fertility...chopped finer than usual might work?
I was hopng I could keep this simple and end up with a mostly decompose mass of roots...you've got me thinkng though

How soon do you need to use the soil? Depending on the ambient temperature, for fine roots a week or two will be enough. It takes longer if you incorporate chunky leaves and stems (Ruth Stout style composting in a pot). Or you can have several batches rolling to speed it up, making compost out of the greens to add to the next pot.

Another way to lighten up the soil is to add biochar. I have good results making fine textured char from vines and charge it with chicken manure tea. It can replace perlite and also gets the benefits of hosting soil microbes and releasing nutrients slowly.

May Lotito wrote:How soon do you need to use the soil? Depending on the ambient temperature, for fine roots a week or two will be enough. It takes longer if you incorporate chunky leaves and stems (Ruth Stout style composting in a pot). Or you can have several batches rolling to speed it up, making compost out of the greens to add to the next pot.

Another way to lighten up the soil is to add biochar. I have good results making fine textured char from vines and charge it with chicken manure tea. It can replace perlite and also gets the benefits of hosting soil microbes and releasing nutrients slowly.

I was aiming for a usable potting soil by late winter/early spring.
That's when I start a lot of seeds in shallow wooden flats.  

I love the idea of biochar although we're just not set up to burn any sort of fire any more since we moved to town.
Might get some ash from the woodfired bakery here and sift out the charcoal...have done that before.  Not the same but still useful?

Still considering how to incorporate the greens...chopping really fine, spreading on the surface or mixing with soil and then covering with a few more inches of soil and then planting the peas and oats maybe?  By then the weather will have cooled.

What I want to end up with is two of these big tubs full of potting soil to scoop out and use when I need some.

Thank you May...you've given me some good ideas and food for thought.

If your primary need is for germinating seedlings, light and fine texture for better soil contact is more important than high fertility. I tried making my own seed starting mix but found it difficult without buying coco coir or peat moss. Big box stores usually have the potting mix on sale in Fall. Getting a load that early also allows plenty of time for conducting a bioassay for contamination.

Judith Browning wrote:Might get some ash from the woodfired bakery here and sift out the charcoal...have done that before.  Not the same but still useful?

You know, it may in fact be decent char. The test is to crush it a bit and rub it on your hands. If it more-or-less washes off with water, no soap needed, you're in the zone. If you have a free source of char (where somebody else has put in all the effort), grab it!

May Lotito wrote:If your primary need is for germinating seedlings, light and fine texture for better soil contact is more important than high fertility. I tried making my own seed starting mix but found it difficult without buying coco coir or peat moss. Big box stores usually have the potting mix on sale in Fall. Getting a load that early also allows plenty of time for conducting a bioassay for contamination.

I want this for both.  I use a similar mix for my seed starting as for potting up. It's just that the soil for flats will be needed earlier and I sift it finer...1/4" mesh rather than the 1/2" I use for small pots.  Big tubs get wood chunks and no sifting.

I haven't bought any coir or peat in years on sale or not and the perlite I used in a mix years ago is still around looking like styrofoam bits  
Trying to avoid all that stuff.

I've mostly made my own mixes with what I have, a little compost, old rotten oak stump,etc...and now this top soil.  
I'm just playing with a way to lighten it up.

Soybeans and wheat up in the first tub
Need to sift more soil for the second one.

Two weeks later from my last photo...I think the winter wheat is too out of sync with our summer weather and grew to about six inches and died.
Have been watering occasionally.

Last week was brutal. I am sorry the wheat seedlings didn't make it. Rye is hardier than wheat so I heard. I am following you and sowed some sunn hemp seeds in a tub of clay. I will see how much roots to get in two months.

I work in a retail garden center. The potting soil that we sell is composed of 50% peat moss for lighter weight and moisture management. I would think that decomposing leftover roots are not going to reduce your soil weight like peat moss would.

Vanessa Smoak wrote:I work in a retail garden center. The potting soil that we sell is composed of 50% peat moss for lighter weight and moisture management. I would think that decomposing leftover roots are not going to reduce your soil weight like peat moss would.

I don't expect it to...just hoping for some improvement

My experiment has more to do with coming up with a more friable seed starting and potting soil than the weight of it although I can see where those two qualities might go hand in hand?

I have a lot of this topsoil available and the seeds so far are from my kitchen bulk organics.

I will be buying cover crop seeds at the feed store soon though but plan to avoid peat, coir, perlite and vermiculite.

And I'll probably get free buckets of sharp sand at the local 'ready mix'...helps keep the soil looser but not lightweight of course.

For now I'm just wanting to see how well the organic matter from the roots themselves loosen things up.

Hi May!
Happy to see your sun hemp tub.
I have not checked for it at our feed store but hope to try it.
Do you find it in bulk near by?

Hi Judith, my local feed stores don't carry any so I ordered online. I planted them a bit too late they only reached the size of flax and bloomed in late September and the root mass wasn't very impressive.  If you want to give the sunn hemp a try I am happy to share some seeds with you.

This September after I harvested squashes I found the soil underneath turned very loose and dark. I dug a pile up and used it for my potted plants. So far they are all doing very well. I am carrying out some experiments indoors with butternut seeds, taking advantage of their robust roots and fast growing speed.

How's the soil in your bean tub?