Monday, May 28, 2012

Soil structure for raised beds

Topping off the raised beds (this was for peas).  I put in soil mix, added in some coir,some Miracle Grow Moisture retention mix, some fish fertilizer, and got a wonderful harvest from this box...
This is a post without a lot of pictures - no matter how hard I try, pictures of soil just aren't that compelling.

But I do want to give you an idea about what you need to do to put together the optimum soil mix for your raised beds.

I came from a background of traditional gardening.  sure, I had spent years shoveling chicken and rabbit droppings from the barn to my parents compost pile, and watched my mom and dad "dig it in" in the fall.  In the spring, my dad shoveled in all his fish heads and fish guts ( kept at the ready in the freezer) to enrich the bean rows.  I didn't really know why they did this, just that you needed to if you wanted plants to grow better.

One of the reasons I chose to go with raised beds is that my parents lived in an area where there was a lot of clay in the soil.  I saw them work for over 15 years to amend that soil to get it to where it could reliably produce  vegetables without bringing in a truckload of manure ever fall and putting every dead leaf on the garden.  I didn't want to spend time doing that.

So the first year I filled the beds with soil mix from one of the local bark dust companies - ours is on Portland Road just before you turn onto Silverton Road.  I have also got bulk soil mixes from some of the local nurseries.  this is basically a good quality topsoil with compost mixed into it - and the compost comes from what plant products are collected at the local landfill.  Plants grew like crazy that first year, but perhaps just a bit more leaf then I wanted.  I knew what caused that - too much nitrogen.

In 1992, while living in Tillamook, we had one of our frequent floodings in the spring.  I worked at the time at a business across from Safeway on Hwy 101.  Safeway had just set out pallets of soil amendments - chicken and steer manure, peat moss, etc.  The flooding carried it across the highway and under our building.  Safeway wrote it off on their insurance, and didn't want to come and get under the building and haul wet, heavy bags of manure out from under our building.  So I got my older girls to help me, and we must have pulled out 25-30 bags of fertilizer from under there.  and took it home, and dug it into all the beds surrounding the house.

I had the most enormous nasturtium leaves that summer - hardly any blooms, but the leaves were as big as dinner plates.  I ask my mom, the garden expert, why the leaves were so big, but I didn't get any flowers.  she just laughed and said it was because of all the fertilizer I had put down.  Fertilizer is a good thing, but you have to have moderation.  Also, you want to make sure that you put down amendments that will cause the soil to interact with it - that will break down and cause your soil structure to improve.  You need soil that will be nutritious enough to support your plants and their needs for elements (like we need vitamins).  You need a way for soil to hold onto water and air - but not for too long - it also has to drain well - especially if you live in an area like we do where you get lots of rain.  Some of the plants I planted in nursery pots from that first year were replanted this spring - the soil was dry and extremely hard, crumbled to dust at the touch.   

You couldn't see any evidence of humus - an organic substance made up of partially or wholly decayed vegetable matter that provides nutrients for plants and increases the ability of soil to retain water.

Water flowed through these pots quickly; the drainage was too good.  So the roots didn't have time to suck up the moisture, along with the nutrients.  In the beds where I had dug in some compost I made from the first year, there was humus, along with evidence of healthy earthworm activity.  Partly the earthworms were there because of the compost that had been worked into the soil mix.  In the beds where I had put additional compost, and the worms had additional veggie matter to feed on, I had from 8 - 15 worms per cubic foot.  In the pots that I had just put soil mix in, with no additional humus, I only had 1 to 1.5 worms per cubic foot.

Why are worms important?  They improve soil sturcture, nutrient flow, organic material breakdown, and organic matter formation (worm poop - called castings).  Earthworms bring up soil from the lower depths, bringing up nutrients from below to root systems, and create paths for air and water to get to root systems.

So if you wonder if your soil is healthy, dig out a cubic foot of earth, and count how many worms you have.

Some people just buy a mix and fill their beds with that - but that is really expensive, and I don't like using a standard mix for all my raised beds.  

For the first third of each raised bed, I lay down a good quality soil mix - topsoil mixed with compost.  Before I put that down, I lay down a layer of materials that need to be composted - leaves, grass, etc. Next two-thirds is soil mixed with a soil amendment like peat moss or coir, into which I have mixed one bag of Miracle Grow with moisture retention beads.  You can get the beads alone, which I have done in the past.  but ACE hardware had such a great buy on their Miracle Gro with the moisture retention beads, I couldn't pass it up.  Over time earthworms will break down the compost materials at the bottom and recycle those nutrients to the top layers.  The bed becomes a dynamic system, as through time you add stuff at the top, and earthworms breakdown those nutrients and cycle them through the bed.

And going forward, I will tell you that I switched over to using Coir about two years ago, instead of peat moss - more on that later.

For my seed starts this year, I mixed my garden soil with Moisture Control, and then some organic compost from FoxFarm - I mixed this in with my garden soil and then sprinkled the surface with coir - and then mixed it all together.  I used this for all my planting medium for seed trays - and for putting over the surface of fine seeds (like lettuce and radishes) and pressing lightly down.

Three soils to mix - regular garden soil, Miracle grow ( on left) and FoxFarm mushroom compost.  Mixed this all together, sprinkled on some coir dust, and this was my potting mix for early peas, romaine, spinach, etc.

For tomatoes, it was important to have a rich soil, high in calcium (to stop blossom end drop), one that would retain water, but also soak up water quickly, and drain well so the roots were not sitting in water.  This is not a natural soil - you have to concoct this soil out of what you have on hand and what amendments you can get.

What type of soil mix you make will depend on what you are growing.  for instance, I have an area in my yard where some day I hope to plant some native plants - some need a mulch that is made up of decomposed tree bark and woody plant debris.  I am saving all that type of material in one pile in the back and letting it slowly decompose - knowing that it will be there for me when I need it.  In the beds where I have plants that can handle the extra nitrogen and higher fertilizer content, I put more compost.  In the areas where I don't want to high nitrogen content to limit my fruit yield, I make sure I mix in more coir to help neutralize the excess nitrogen.

So what is coir?  I can start answering that by explaining why I no longer use peat moss.  

It would take too long to repeat what others have said more eloquently about why using peat moss is a bad idea, so here is a link to one of the "rants" about using peat moss:

Basically, Peat Moss is not a renewable resource
Once dry, it doesn't really absorb water again, making it undesirable as a soil amendment
It breaks down too fast, packing in those small spaces and making it difficult for plants to get air.
"mining" of it is ruining whole ecosystems and wetlands - do you want to be part of that?

So, what else can you use?  For years, I bought bales of hay, shredded them, put them through my leaf shredder and created a mix of dry fluffy stuff that I mixed with soil mix to lighten the soil, put organic matter into it, etc.  but this wasn't a great answer.  I got a lot of hay seeds mixed in there and spent a lot of time pulling grass seeds out of the garden.  And when it started breaking down, it just added nitrogen to the mix. 

I found the answer a couple years ago when cleaning up in the fall, and I had to do something with the coconut fiber mats that lined all my trough and hanging planters.  I paid good money for those, and didn't just want to toss them.  So  shredded them up with a scissors, and made up a soil mix for some pots I was going to use for overwintering some plants.  Six months later I was impressed.  Impressed with the health of my plants, the soil structure, the earth worm presence.  I set out to find some soil amendment that had coconut husk in it.  Fortunately, someone else had this brilliant idea also and it was there in the marketplace waiting for me.  

I have used a couple of different brands that I have found in different gardening centers, but the one I am currently using is:  Du Shoup LLC's i-Coir Coconut Coir Pith, and I get it in the large block.  Here is their website and you can access information on Coir, Coir vs Peat Moss, and also where you can buy it in the Northwest:  (They also belong to the Oregon Association of Nurseries, so I am supporting a local business).

I bought mine at Ace Hardware on Madrona in South Salem.  It was a lifesaver for me.  I didn't finish getting all the soil out of the back of my truck when we had a thunderstorm last friday night.  My truck bed was full of mud and water.  I unwrapped the brick of coir, put it in the middle of the mess, pulled mud around it, and within an hour, the coir was expanding, pulling the water from the soil.  two hours later I was able to mix the coir in with what had been mud, but was now workable soil.  I mixed it all up, and had some great soil mix to help re-pot my 3-yr old grape vines.

Cosmic Coir from  I can't describe how the soil feels when you mix this with it - you just know that you are doing great things for your soil.  I know that I will water less this year then last year mixing this in - and that means less stress for my plants and higher production.

Now it may be that you don't have a lot of money - I don't either.  So pick up a block of coir a month if that is all you can do, and work as much as you can into your raised beds.  I plan on getting another 10 blocks this summer, and gradually working more into all my beds as I get done harvesting.  That, along with some finished compost, should give me excelled soil structure.

And remember, you don't need to shovel in and mix the dirt around - why disturb the worms who are doing all that hard work 24x7 for free for you? Sprinkle coir and compost, chopped straw, leaves, whatever you have to put on your beds, mix it in gently with the top couple of inches, and just let it go.  The worms will do all the rest of the work.

If you are still getting rain where you live, mixing in coir will help it become lighter and more easily worked.  Good luck in your gardening endeavors.



  1. Wow, thanks for the info on the coir - I'd never heard of it before. We felt compelled to buy some peat moss a couple years ago for our blueberries. We felt guilty about it then and still do! We'll have to see if we can get coir around here.

  2. Thanks for the info, I've just purchased 11 ton (when expanded) of this stuff to add to my allotment soil which is full of clay.

  3. An update to this. I learned from my son to bury wood in the bottom of the beds - pieces of cedar board and 2x4s, wood limbs from tree trimmings, etc. These are then covered with compost to even out the PH - and then the rest of the soil and amendments. this is an example of hugelkultur - one of the principles of permaculture. Even thought I increased the amount of raised beds I had by a third in 2014, my water bill didn't go up - and it was a drier year than previous years. For more info on hugelkultur, you can go to this website: I also recommend the book, Gaia's Garden - My son gave this to me for Christmas a few years ago, and it has been a wealth of information.