Topsoil for exposed clay subsoil

Hi all,

We just took off about 12 inches of soil from our yard - it had been covered in concrete for decades before we moved in. Needed to grade and lower the overall level of the yard for various reasons. We now have a 35' x 40' area that's clay subsoil with no topsoil. We'll begin landscaping in about 12 months. What do we put on top? Mulch? Compost? A combo? And how many inches? We can amend and bring in topsoil if we must before we plant (edibles, lots of flowering plants for pollinators, and a few trees and hedgeseventually). For now we want to start building that topsoil from what we've got.

hey leah,
welcome to the forums.

have you thought of growing a cover crop on that soil? this year i dug up a small hügelkultur-bed and the soil is very clay-rich. i planted peas. they grow ok. they somewhat protect the soil from weeds, their roots loosen the soil, add organic material and fix nitrogen. and i get a harvest.

you should start composting as soon as possible.

maybe you could grow hardy plants like comfrey and mullein, that will start growing now and will help you very much later.

when you have your garden-layout planned, you could start building the beds with the "lasagna technique", where you add layers upon layers of compostable material onto the soil.

good luck and blessings
tobias

@Tobias.

Thanks for taking the time to respond.

You know, I'm not ready to plant yet. I have a small child and want her to be able to run around and play while we figure out a landscape design. Do you have thoughts on whether 4-5 inches of mulch is enough, or whether I should layer comoost under the mulch, or just being in topsoil with mulch over it that will sit for quite some months while we figure out what to do?

hey leah... it depends. for veggie-beds i would take more time and effort to build the soil. it will imporve quality and healty plants will save you time.

would you be able to bring in topsoil for a reasonable price?

if you could get manure, leaves, spoilt hay etc. then you could start composting that by now, it will be ready for next year.

it depends on what you can get.

for beds it would be good to loosen the clay, then add topsoil, then compost, them mulch it. the mulch prevents weeds and retains moisture. and will help earthworms. but it can be done with less.
start with what you have or can easily bring in. add layers of mulch and compost every year on top and you ll be building your soil while growing stuff.

you could try something with your kid. get dried soup peas and lentils. soak them overnight. loosen the clay in one area. throw the seed. rake it in a bit. and see what happens. maybe add a bit corn (popcorn-making corn will often sprout). maybe some sunflower seeds. bury some potatoes. and just see. you ll create your own composting material. you will improve your soil. you will attract animals (like worms). and you will probably get a harvest.
that can be play for the child, but it will teach much about gardening.

edit: one of the first things we did was to sow calendula and tagetes. it just needs 1-2 m² of somewhat ok soil to grow many. then we saved seeds. this is a good task for a child. the calendula self seeded. and we could sow them in many places and grow starts indoors for early planting.
these flowers are easy to grow. but they help the soil. they attract insects. they look great. calandula flowers are edible. you can use these to cover ground until winter and then use the (improved) soil for other plants next year.

Leah, I second the lasagna layering, and maintaining a thick layer of leaf mulch over the top of it.  You probably know that clay soil should never be exposed to the sun, and mulch with layers underneath works really well.  Once the clay soil stays damp from the mulch and amendments the worms will come up and it will be easy to work.

Are you, by any chance, planning an area for a swing set?  That is a good way to give kids their own zone where they can play and be active, and not be running and digging around where you've got vulnerable little vegetables.  My best childhood friend and I still talk about our legendary swing set and all the great stuff we did on it, even pinning sheets on with clothes pins and making it a fort.   We made games out of swinging, then jumping off the swing and running.  It was well secured to the ground so we could do just about anything on it.  

One easy method for building topsoil on top of bare clay is to tile a single layer of square hay bales on the area and keep it moist (rain or watering).  It will break down over the course of the summer into an inch or two of topsoil and, depending on its seed content (determined by when it was cut), may produce a lawn/pasture of the type of grass the hay was made from.

Thanks all for your responses. I've heard from landscapers around here that it's fairly awful to have had so much soil hauled away, and a big problem to have only clay subsoil. I want yo plant a mindfully planned garden with fruit trees, edibles, flowers for cutting / pollinators / hummingbirds / butterflies. Apparently roots will get stumped at the subsoil if it's not properly attended to and will die? I love the hay idea, but I don't want a hay lawn. It's a small yard - 35x40, that will have many jobs. I don't have space to create my own compost pile, though we are lookin at a contained backyard composer. Rats are definitely an issue. Any idea what all this means?

I want yo plant a mindfully planned garden with fruit trees, edibles, flowers for cutting / pollinators / hummingbirds / butterflies.

In 2013, this was covered with landscaping fabric and nothing else.   No topsoil to speak of.  So compacted, you couldn't get a shovel into it. No earthworms.  Scorched earth.

I mulched it, planted part of it with a cover crop, turned that in, and mulched a few more layers as the old layer of mulch decomposed.  It is now the favorite part of my garden.  In spring, it's pink and yellow with lupines, tulips, chives, peony, digitalis.   Then the salvias bloomed and it was wildly purple.  Now, self-seeding calendula, tall phlox, daikon radish, crocosmia, comfrey, anise hyssop, lemon balm, perennial garlic, and more.  One a few good mulch layers has a couple of years to break down, all this stuff is easy to grow.

Anyone have experiment with clod-breaker amendment? Is it effective? Useful? Any problem with it?

@kputnam - That's beautiful! So it's not dire, our yard. So confusing though. I'm looking for a soil expert in my area to come look at what we've actually got right now and give me advice. Thanks for the response. I'm new to this, and I'm learning from all of you.

Leah, do you  mean the grinding machine, Laclau machine or gypsum or what?

if you are getting clods in your clay soil, then you need thicker mulch.  The clods in a garden that get  in one's way only happen when clay is exposed to the sun.  

The original clod breaker for clay soil is water.   Don't drown your clay, but get it wet, and walk away for 20 minutes, give it time to absorb the water, and it will fall apart under your shovel.    If you don't have the time, cover it with a tarp or thick fabric, a thick layer of mowed weeds, keep it wet but out of the sun until you can come back with a shovel and add as much organic matter as you can.  I add granite sand as well.   I keep the leaf/mowed weed mulch at a minimum of 6 inches, that shrinks to a dense 3 inches.  Worms come up, no clods.

Once there's moisture and organic matter, and nice cover crop would be helpful.

I looked at the clod grinder website, and honestly, grinding clay is a gross misunderstanding of how clay works.    Even if you wanted to grind it, the minute it gets exposed to water and the sun it's going to turn to clods again.  Even pounding rain sets clay up to turn into clods.  So it just doesn't make sense.