Soil Mix for New Raised Beds

PNWMagpie(Zone 8)May 15, 2012

Hello, I've searched and read LOTS of threads in various forums here, but haven't seen anything that matches my situation *quite* well enough to answer my concerns - I'm new here, so please forgive me if I've overlooked something or am posting this in the wrong place!

I live in the Willamette Valley in Oregon, right up against the foothills of the Coast Range. The 'native' soil in my area is heavyyy compacted clay, so I've been putting in raised beds for everything - vegetables, herbs, lots of berries, some small fruit trees. Last year I filled some beds with straight compost (municipal, but 'approved for organic use'), and some beds with a mix of same compost + coir, sand, pumice + small amendments (limestone, oyster shell, etc) - I based the various mixes on Richo Cech's recipes in 'The Medicinal Herb Grower'.

This year, the compost-only beds are MUCH compacted and hardened and 'crusty', while the 'mix' beds have much softer texture and drainage, not near as much shrinkage - well, I s'pose that's not a huge surprise, really.

But okay, now HERE'S my problem - the mix I made last year was, in the end, SUPER expensive (and a major project to mix, given my small working area - soaking coir in the wheelbarrow, mixing on a tarp on the driveway, etc)- and, the more I ponder the coir, I'm really not feeling good about using a material that has NO native relation to this area and comes from so far away - I decided to use it in place of peat (which I stay away from altogether for several reasons), but yeah, upon further consideration I'm not so sure the coir is such a good choice either, for here, for me.

Now - the same place I got the municipal compost also does custom mixes - they don't have coir anyway, and they DO have peat but I don't want to go that way - but, they also have various grades of bark chips, along with sand and pumice and of course the straight compost.

So FINALLY, HERE'S MY ACTUAL QUESTION: Could I use wood chips in place of coir/peat? My chip options (with descriptions directly from their website) are -

Medium Fir - Deep red, freshly ground fir bark screened to 3/4". A great topdressing for planting beds; also use as a filler component in potting mix.

Premium Fir - Aged ground fir bark with a deep red color and screened to 1/2". A premium topdressing for planting beds; also use as a filler component in potting mix.

Hemlock - Aged ground hemlock bark screened to 3/4"; chocolate brown color. A sliverless topdressing for planting beds; ideal for people with children or pets.

Alder Sawdust - Ground and shipped directly from a local alder mill. Excellent for frost prevention, mud control and bird deterrent or as a thin topdressing to retain moisture in recently seeded lawns.

Cedar Chips - Cedar woodchips sized to 2" to 4". A long-lasting barkdust alternative, cedar chips make excellent

bedding for pathways, play areas and kennels.

...So, what about the premium aged fir (and/or the fresh medium fir?), mixed with the compost and pumice - and sand? - orrr, they also have what they call 'sandy loam topsoil', which by itself appears wayyy more 'sandy' (gritty, dry) than 'loamy' or 'topsoilish', but could also be used as part of a mix. WHICH elements would you advise I include, AND, in what proportions?? Can I put together a 'complete' mix from the available materials, or would I still need to add in *something* to round it out? I've read that fresh chips can lock up nitrogen, apparently, but is their larger size an advantage over the finer aged chips? Like, maybe using them as a mulch, rather than mixing-in?? Or...??!!?

I'm at the point of having pondered this SO much that I can't think straight anymore - I've seen that there's lots of super-knowledgeable-experienced folks here, so any help sorting this out would be sooo much appreciated!

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You're right about the chips robbing the soil of nitrogen. Depending on what you're growing it might work. On the container forum they discuss a blend of pine bark + other ingredients.

A load of the sawdust piled up & mixed with a green like grass clippings or plant waste will be good to add to your soils about a year if you turn it now & then. Sometimes, manures come with sawdust bedding, so that is a good combination to compost for further use.

What kind of plants would this new raised bed be for growing?

Are you filling a new bed or topping off an existing bed?

A sandy loam topsoil mix + 6" organic matter would be a good way to go if you need to plant right away in this bed. Use compost or composted manures and mulch with dried grass clippings, shredded leaves, chopped straw, used coffee grounds, etc. If you're growing vegetables, you also might want to add some pumice like you said and a complete organic fertilizer. Over time you won't need as much fertilizer to grow great vegetables.

Each year continue to add more organic matter to build the soil you want to use for your gardening. It takes a lot of it to keep up the soil, so it's nice to build some home compost piles for a good supply. You could also compost in place in & around your existing vegetation in perennial or shrub beds.

I'm in western WA and we also have glatial till, so that when you dig a hole you get a pile of rocks. Those rocks are moved elsewhere in our landscape. Eventually the annual vegetable bed areas have become good soil for our perennial fruits like raspberries and strawberries.

Our technique has varied over the years, but usually we've sheet mulched with manures and bedding in the fall piling up to 12" on a bed then turned in the spring. Plant & mulch. By summer's end it's shrunk again, so more sheet mulching. It's amazing how much organic matter is used up.

In my garden boxes with wooden sides I also add compost whenever I harvest a crop then replant. In fall apply manures, used coffee grounds, and lime. In spring I've done different things different years depending on my energy level. Remove mulch to the sides before planting transplants. Rake smoothish & plant. Turn over with garden fork, rake & plant.

For direct sowing seeds I rake a bit more later in spring or cover with a slight layer of screened compost to smooth out the bed. It always seems to work.

For perennial and shrub mixed borders we just mounded the soil with the layers of compost ingredients and after a few months planted through the layers. We've spread mulch 2x a year since and those are much easier to work beds. Where we had existing vegetation that soil is still quite hard & rocky. As I move things around I come upon that rocky slippery stuff and add a lot more compost to a section when replanting.

I hope that helps ~ Corrine

    Bookmark   May 16, 2012 at 11:21AM
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PNWMagpie(Zone 8)

Thanks for such a generous response, Corrine! There's actually several built-this-spring beds that need to be filled from scratch, and several beds built and filled last year that need to be topped up (some as much as 50%, such as in the veggie beds that had a high ratio of compost).

Overall, about 1/2 of the beds are for annual veggies (tomatoes, peppers, beans, lettuce etc), 4 beds are for herbs (fast-draining annual, fast-draining perennial, moisture-retaining annual, moisture-retaining perennial...more or less), and the rest are fruits - established strawberry, raspberry, and lingonberry, with blueberry, red currant, and gooseberry new this spring. So, some beds are/will be direct-seeded, while others are mostly getting transplants, and still others have established plants that need topping up - thus I feel like I've got a little bit of EVERYthing going on, and I'm behind on all of it, ha. And yes, most of it will be more-or-less immediately planted/seeded as soon as the soil is in place.

I THINK if I order a custom blend of compost, aged fir bark, sandy loam, and pumice - plus some medium fir bark for mulching - that *should* suit everyone (with the inclusion of plant-specific/bed-specific small amendments added in as I go, to cater to individual needs). I'm just not sure what proportions would be best for the 'base' mix - like, if I've got a roughly 50/50 pile of compost + aged fir, how much sandy loam and pumice would I want to add to that?

I like all your notes about how you work with your beds THROUGHOUT the season - I'm hoping to get into a rhythm of maintaining the beds in that way, instead of this desperate all-at-once crunch in the spring, so those ideas are reeeally helpful. Thanks again for your thoughts!

    Bookmark   May 16, 2012 at 3:11PM
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gardenlen(s/e qld aust)


if you don't dig the chips in or cover them with medium, the nitrogen issue won't occur. if your clay dissolves in water then add oodles of gypsum.

see our presentations, we use what is available cheaply.


Here is a link that might be useful: lens straw bale garden

    Bookmark   May 16, 2012 at 4:20PM
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1) Gypsum is useless in PNW soils. It is only of value in sodic clay soils.
2) The premium fir bark is about the right texture and dimension to replace coir or peat...smaller would be better :-)
3) Overcoming the nitrogen issue is extremely easy - just mix in some alfalfa meal to your beds and you are good to go.

I'd ask the compost/soil distributor for a garden planting mix. Typically this is a 3- or 5-way mix that is good for growing just about anything. Fast drainage and with an adequate nuttrient load, this is an imported soil that can be used in virtually any gardening situation (aside from containers) - new lawns, new planting beds, raised beds, etc., etc. Extremely common with just about any PNW bulk soil provider.

    Bookmark   May 18, 2012 at 6:06PM
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PNWMagpie(Zone 8)

gardengal, ooh, thanks so much! Good to have some confirmation that the aged premium fir should work out fine, and I already have alfalfa meal in my stock of amendments - yayyy! =) Yeah, I hadn't heard of anyone using gypsum around here, and it's not one of the mix options anyway. They do have a ready-made 'planting mix', but it's just compost + topsoil - or beyond that, potting mix, which is compost/peat/pumice. The only way to include the aged fir chips I want to try is to have them do a custom blend, so I'll go with that. Still trying to figure out a good ratio of compost + aged fir + pumice, and whether or not I should also have topsoil (very gritty/sandy stuff) or sand added in - but I sure appreciate your input, AND the alfalfa tip!

And len, your straw bale bed looks great - I'd read about using bales to frame a bed, but for my garden that would take up a lottt of my planting space. Although, I hadn't thought of setting containers on top of the bales! I have an edge here where that might actually work really well, so thanks for the idea. =)

    Bookmark   May 18, 2012 at 10:05PM
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Would be interested in a follow up from OP. Which mix did you use & how did your garden grow in 2012, 2013 and so far this year?

We've done something different since spring, 2014... moving our garden to a larger clearing in the woods. We now have new beds of fruits & vegetables in an area 50'x80' to be fenced from deer with a lot more sunshine. Everything is raised up on top of the new soil that was previously covered with brush & trees that were too close to buildings. Goats plus chain saw helped clear the land. Rocky glatial till makes digging holes difficult, so we just layered up. We planted in raised mounds of chips, with composted manures and topped with our previous garden soil.

The wooden sided beds were replaced with concrete block beds. Three are 2 high, so we added a lot of composted alpaca manure to get the volume needed. I'm grateful for them because I broke my ankle last month & have been able to harvest what I had already planted before my fall. All the ground beds holding perennial fruits & vegetables are inaccessible to me until my fracture has healed, so I my family & some hired help have worked in those.

It will be interesting to see how these beds continue to produce with no tilling.

    Bookmark   May 31, 2014 at 2:36PM
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