Fertile Inquiries – Creating and Sustaining Soil Fertility

Sharon February 24th, 2009

Gardeners like to compete with each other over who has the worst soil to start.  One will argue for his hard clay, baked in the sun, another for her sand, without a trace of organic matter.  I’ve got my own candidate for the worst soil ever – the stuff in the beds around my house.

Oh, texturally, it is among the best I’ve got – sandy loam, warms up nicely, isn’t too wet like much of the rest of my soil.  It had some nice enough foundation plantings, and I mostly ignored it for the first few years I was here.  But a couple of years ago, I decided that I wanted to make use of this growing space, and then I discovered that my soil, was, well…dead.

By dead, I mean there wasn’t a living thing in it.  Not a beetle or a spider, and especially not an earthworm.  It was weird.  I knew that some previous owners of our house were umm… shiny green lawn people, and I don’t know if that has something to do with it, but this stuff was “Its dead, Jim” dead. 

So we embarked on a campaign of soil improvement.  Any kind of soil improvement has two parts.  First, there’s getting your soil up to speed.  In some cases, this might not be much – maybe some ashes from your stove or a little lime to even out some acidity, or maybe a little rock powder for trace minerals, or a light dressing of the rabbit poop your rabbits make sure you get anyway.  If your soil is basically in good shape – you’ve had a soil test and you know that it is high in organic matter and sufficient in macro and micronutrients (check out Aaron’s soil fertility basics if these concepts aren’t familiar).

But what if it isn’t?  What if you’ve got dead soil, like mine, or rock hard clay, or soil (also like mine) that has been leached and has too much water in it?  Again, there are two projects here – the first is the short term building of soil so that you can get to gardening.  The second is the long term maintenence of soil health, and the addition of more organic matter, so that eventually, your soil can hold enough organic matter to save the world – or at least sequester as much carbon as possible.  Plus, things will grow better.  Win-win.

My favorite way to build soil on something that is completely unworkable is the lasagna method, which is pretty much sheet mulching with some dirt or compost on it.   This makes raised beds, which is good if what you have is either wet or rock hard, or if you are, say putting your dirt on gravel or something toxic.  It might be tough in a dry, hot climate though – raised beds dry out and warm up in the spring earlier, and keeping them wet might be tough.  In that case, you might consider digging into the ground, creating sunken beds with the same mixture.

If you need to amend soil, you’ll have the choice of synthetic or natural soil amendments.  Generally speaking, you’ll want the natural ones.  I’m not a complete organic purist – I think there are times when artificial fertilizer use is justified.  But there’s a price to be paid for its use, and care is needed – otherwise you can end up contaminating your water supply, wasting your money and depleting your soil overall.  I don’t generally use synthetic fertilizers, and if I were to use them, I’d use them only on untilled soil with plenty of organic matter added, in small and precise quantities. 

You can buy an organic fertilizer mix, or you can make your own.  I generally use a mix of alfalfa or soybean meal, rock phosphate, and wood ashes, along with greensand and kelp, as well as occasionally special additions to deal with soil types or plant special needs.  But I don’t know about you, but I can’t mine rock phosphate from my property, nor do I produce enough alfalfa to fertilize my garden.  So this is not a long-term sustainable project.  I use these amendments sparingly, where they are needed to bring soils up to basic fertility. 

Then, we try to keep it there.  That means cover cropping a portion of our garden every year, integrating dynamic accumulator plants into our plantings (these are plants that bring up nutrients from the subsoil), undercropping with nitrogen fixers (these plants fix nitrogen from the air), mulching (we try to grow as much of our own mulch as possible in place – another good use for undercropping – a nice planting of buckwheat under tomatoes, or white clover under garlic can provide a living mulch and then the next planting cycle’s mulching materials), and the heavy application of organic material – that is, compost and composted animal manures.

Every time we take something off of the soil, we are removing nutrients from our soil, and depleting, to some degree, the organic material available to them.  High levels of organic material are essential for soil life and health – so faced with dead soil, the first thing I did was put my turkey poults in a chicken tractor on top of the border for a few days.  The easiest way to move the poop to the garden beds is sometimes to move the poop makers there ;-) .  Now since this was raw manure, I made sure there was plenty of bedding, and I wasn’t planting food plants there right away.  Had I needed to use it immediately, I would have switched to already composted manure, and gotten out the wheelbarrow.

Next, I planted the foundation plantings to annual alfalfa, since it was already summer, and warm.  Cover crops generally have a couple of seasons – they are spring, summer or fall sown.  You sow the fall crops to overwinter – to hold soil in place, and add organic material.  Winter rye, hairy vetch, fava beans (in some climates) are all common winter sown cover crops.  Spring sown crops are generally cut down in summer, and either stay in place all season (things like red clover), providing multiple doses of fertility and green material, or they are cut down (oats, say) to provide organic material for the fall garden.  Summer crops (buckwheat, annual alfalfa) can go in after the peas or the early lettuce, and grow fast and fill the space until fall.  For a site you don’t plan to get to for a year or two, perennial crops can do a lot to regenerate soil.

Cover cropping is very place specific – the best crops are specific to your climate, seasons and locality, so talk to your cooperative extension.  They are a powerful tool for building fertility, adding organic matter and improving soil, and one that is worth getting to know. 

My goal in the long term is for these beds to provide a warm, dry, moderately fertile site for mediterranean herbs and a few flowering perennials.  That is, I wasn’t trying to produce fertility for growing heavy feeders, like greens or corn.  So after the alfalfa, I added some greensand and kelp, a light layer of compost, and planted into the mulch I’d already established.  In went lavender, oregano, several marjorams and thymes, a rosemary that probably didn’t survive the winter this year, and some plants that like or tolerate similar conditions of slightly dry soil, lots of sun and only moderate fertility – catmint, echinops and malva.  And they’ve thrived. 

Many perennial plants make wonderful fertility enhancers to annual gardens - whether perennial nitrogen fixing shrubs, whose leaf litter and root nodes enhance the trees and perennial plantings around them, comfrey and stinging nettle which can be cut for mulch or compost, small trees integrated into garden sites to provide leaf mulch, or perennial living mulches.  This is one of those things that has potentially enormous long term yields, and has really only begun to be explored in a deep way.

The best soils for sequestering organic matter will be those that are in perennial plantings, that have constant inputs of organic matter – these include forests that are enriched yearly by leaf drops, permanent pastures which are manured by grazing animals (Peter Bane, editor in chief of Permaculture Activist magazine found that Joel Salatin’s grazed pastures sequester as much carbon as a similarly sized forest after decades of grazing), and perennial gardens that are carefully managed to provide their own needs.

I maintain fertility in the perennial planting I established in these beds by the occasional dumping of animal bedding on the ground, permanent mulch, wood ashes from our stove, and a strewing of kelp.  I’ve also grown an annual crop of chamomile, a good dynamic accumulator, and left everything but the flowerheads in place.  I give the whole thing an occasional boost of nitrogen by dumping dilute urine over it – urine is safe and diluted 1-7 (1-10 if you don’t drink enough), it provides a real boost to plants. 

More demanding annual feeders get composted chicken or goat manure, plant compost, weed and manure teas.  Other plants might also get living mulches, and I rotate plants as wisely and carefully as I can, following the heavy feeders with nitrogen fixers or light feeders undersown with nitrogen fixing cover crops.  My whole garden gets rotating quantities of worm casting to supplement the soil and improve its texture. 

Meanwhile, in maintaining, we try to put back what we take off.  Crop residues are left in place, either chopped down and incorporated into the permanent mulch or they are burned in our woodstove (for heavy, dense stalks) and returned as ash.  Some of the nitrogen is returned in the form of urine.  We mulch as much as possible with our own mulches – grass clippings, leaves and plants grown for compost or as mulch plants.  We try not to steal too much from any one other place – but we gratefuly take things people discard, like leaves from yards when we venture into suburbia, or horse manure from our horse-keeping neighbors.

Animal manures have a very powerful role in gardening – in a perfect world, we’d compost all human manures until they were thoroughly pathogen free, and restore the soil with what we take off.  But whether this is safe is debatable, and anyone who shares food will not want to risk a lawsuit.  So composted animals manures are a powerful tool for maintaining fertility – one of the reasons that polycultures of animals and plants are generally more effective than either alone.  We use composted human manures only on decorative and tree plantings.

Two particular ways of maintaining fertility deserve mention here – fungal soil support, by mycorrhizae (tiny fungus  that colonize the soil) and terra preta.  Mycorrhizae have a symbiotic relationship with the roots of many plants, and can enhance the ability to plants to uptake nutrients and deal with water stress among other things.  Many soils are fungi deficient, and an application of mycorrhizae can improve your plants ability to absorb the nutrients in your soil.

Terra Preta is a fascinating subject – and one still uncertain.  Terra Preta involves adding plant based charcoal (ie, not the briquets at the grocery store) to your soil.  What this does is still a matter of speculation – it isn’t clear, for example, whether the charcoal itself or the organic processes it enables are actually what creates the rich soil involved.  Nor is it clear that all soils respond equally well to terra preta inputs – for example a study found that boreal forest soils did not seem to respond to biochar applications.  That said, however, there have been some fascinating results – biochar supplemented soils seem to stimulate nitrogen fixing in legumes, for example, and while charcoal supplemented soils enable plants to take up more minerals, the soils deplete more slowly.  I’d encourage everyone to consider experimenting with biochar as a way of improving your soils. 

We’re not a closed circle by any means – we still take advantage, as long as they are available and we can afford them, of valuable amendments.  But the idea is to lose as little as possible, while getting the best possible balance between improved soil, the health of the world, and a system in which you need to bring in a little less from offsite each year.


9 Responses to “Fertile Inquiries – Creating and Sustaining Soil Fertility”

  1. Callion 24 Feb 2009 at 1:36 pm


  2. risa bon 24 Feb 2009 at 1:51 pm

    Gee, I’m hoping “Meh” in this case means “wow, that was a lot but I’ll reread it later and take on my own soil issues.” This was an extremely useful post.

    We’re gardening on top of a heavy, unforgiving clay, filled with round river rocks, that has us doing practically everything right in the mulch layer. We bought two tons of hay last year, and are walking back and forth with wheelbarrow loads of poultry bedding, buckets of ashes, liquid manure. When I plant spring crops, I bore a hole in the mulch down to ground level, cloche the spot for a week or two for warm-up, come back, pour in a canful of potting soil, lay out the seeds on that, pour in another canful, tamp it down flat, water lightly, and stick the cloche back in the hole. Things are that bad. On the other hand I haven’t had to wrap tons of clay around tiller tines in a long time because I don’t till this muck any more (it goes from muck to “bricks without straw” in like, two days) and we DO get crops.

    So, if we want the land to give us something, we have to put something in first, like our blog author says here … one thing the soil is not, is a credit default swap.

  3. Lanceon 24 Feb 2009 at 2:29 pm

    Ethical Gardening from an Animist Standpoint:


    “The idea took a while to grow on me but I found through discussions about many aspects of permaculture, and from an animist perspective, we need to encourage life, and encourage interaction between life forms.

    So, instead of digging, plant some plants that will do it for you, and mulch like the forest does, and encourage digging worms and insects. Save yourself work by delegation.

    Grow a bunch of clover to help fix nitrogen and feed the deer and rabbits. They will prefer some lovely clover to anything you could be growing in your garden! Plant some alder specifically to thin every year, transport the logs to places on the rest of the land that could use swaling and butressing, and grow some fungi or something as well. Maybe a native willow or two? If you decide to grow anything, double it!!”

  4. Lanceon 24 Feb 2009 at 2:31 pm

    more from the same site:

    “We don’t have gophers, but we do have moles. And what a blessing they are! One resident at the farm said he wanted to get more cats so that they could get rid of the moles. I explained what a loss that would be, given that the moles aerate and turn-over the soil masterfully. Also, the soil of the mole hills the make are excellent soil to put on top of our raised beds! Its already mixed, and fluffed too.
    I filled several 10 gallon buckets with soil from only about 1/2 the molehills on the farm. I did not want to hog it all. Also, I make sure that there is enough soil left that their burrow entrance is covered so that I don’t expose them to predators.

    You can do the same thing with gopher hills.

    Moles are awesome!”

  5. ctdaffodilon 24 Feb 2009 at 2:32 pm

    ok – I’m going to go ahead and ask –
    Where is the best place to get a soil sample tested…..since I won’t get raised beds done for my gardening this year – I guess I should have my soil tested before getting a delivery of composted manure and tilling it under……

  6. Fernon 24 Feb 2009 at 2:40 pm

    Ct – check with your county farm extension office.

    Lance – we have lovely chipmunks here, aerating away (and entertaining our indoor cats). They are great fun.

    Sharon – I’ve got the ‘mulch and some soil’ on top of hard hard hard clay going in one of my beds. Didn’t produce much last year, but it has VERY happy dandelions overwintering.


  7. Maeveon 24 Feb 2009 at 3:48 pm

    My soil is moderately healthy (as in, plenty of worms), and more sandy than clay, though definitely lacking in loam. My long-term goal is to get that rich black earth thing going on.

    Adding in compost, organic fertilizers, and some mulch are all on my game plan. I just don’t want to disrupt the mini ecosystem too much all at once, and I would be really disappointed if my efforts at garden fertility eliminated all the random flower volunteers that popped up last year. (At one time there had been a garden there, but it was grassed in, so I had to dig out the sod last spring in order to plant. I had Johnny Jump-ups pop up all over the place. Simply lovely.)

    I used to have a source for horse manure (alas, I had no garden then), but they have since given up their horses. So I’m keeping an eye out for animal inputs.

  8. TJon 24 Feb 2009 at 7:16 pm

    we have a worm bin, but not a compost pile (we used to but – rats…)
    so what to do with a little piece of bread that got moldy, and today a can of cod liver that looked bloated ?
    Tell me if this is VERY wrong – I bury it all – under trees and where ever I can dig 6″ without destroying too many roots. I don’t exactly know who will consume the bad cod liver and its associated botulism. But something did consume a chicken carcass – nothing left after only a month. May be the gophers, may be raccoons may be something else – but whatever ate the stuff – must poop too. So all the organic matter goes – the only problem is all I have is 5000 sq. ft that includes the house and the drive way etc.


  9. Apple Jack Creekon 24 Feb 2009 at 9:36 pm

    Oh, your link to the lasagne gardening site is EXACTLY what I needed!

    I have a nice garden on reasonable soil, but it’s former pasture and the grass is *very* well established. Last year I put in two raised beds, filled with purchased peat moss and planting mix and grew a decent crop of stuff.

    This year I want to expand, and was thinking with dread of having to go out there and dig up the soil, turn over the sod, and find the dirt underneath. You’ve saved me! I can lay down newspaper (time to start asking people to save me some), and I have a two (three?) year old bale of hay sitting in there that is just waiting to be rolled out on top of everything. In fact, last year I rolled some of it out on areas I planned to plant in future, to kill the grass and compost in place … so apparently I was on the right track. :)

    We do have animal manure (sheep and a couple of cows) and a nice big compost pile going from last year’s barnyard waste, so with luck, we’ll be able to get those new beds in place without me needing daily visits to the chiropractor!


Trackback URI | Comments RSS

Leave a Reply