Okay, I take it you're buying this compost? If you're keeping the bed mulched with shredded/chipped hardwood, then that should suffice for building soil organic matter over time. It will need periodic replenishment as it decomposes. Just sprinkle on a bit of your favorite nitrogen source periodically - bloodmeal, soybean meal, alfalfa meal, urea, etc.

If you want hasten the buildup of organic matter in your soil, then after the wood mulch has decomposed for a year or so you can turn/cultivate it in, as best you can, to the top few inches of soil, add some new compost on top if you wish, then add new mulch.

Or if you just want to periodically add more compost for nutrients, then do so in very modest additions, and do it when you top off the mulch. First. add the new compost on top of the existing hardwood mulch, mix it a bit with a rake or whatever tool works best for you, then top off or dress with a layer of new hardwood mulch.

Thanks for the reply!

Yes, I am buying the compost. Our previous attempts at composting was a smelly disaster because no one wanted to do the work of turning the pile over, etc. I've now found out that my municipality gives some compost away, so I'm trying to get some this weekend.

I am trying to add compost to the soil because I have my doubts about this wood decomposing fast enough to do much. My soil is fairly heavy with clay (the few worms I saw had hardhats and mining picks) and I am hoping that a lot more organic material will encourage the worms to make my soil better, as well as hoping to cover for any goofs I make in not applying enough fertilizer to my plants as I learn the ropes. I've also had a couple of shrubs die because the clay soil was just waterlogged, and I think the roots rotted.

So, you're saying that once my mulch has aged a bit I can just add the compost on top and mix it in a bit, then add more mulch? I had read that the wood decomposing would rob the soil of nitrogen, so I was worried about it not being right at the surface.

Basically, yes.

Wood mulch is a high carbon material, and if it is mixed with soil before it has decomposed it can divert nitrogen away from plants. In the long-term it's a temporary effect - the nitrogen will come back as the decomposition progresses. In the short term, it can lead to a nitrogen deficiency for your plants. The solution is simple - add a bit of a N source to help the wood mulch decompose efficiently without drawing nitrogen from the soil. The idea is to essentially sheet compost the wood mulch in place.

I see you're in a northern climate (eh?). When I was a mid-Michigan gardener for a dozen years here is what I did with my permanent landscape beds. Most of the mulch was applied in early autumn for winter protection. At that time I would add a thin layer of a manure compost on top of the existing mulch (like 1/4"), and then top off with a wood mulch for winter protection - no real mixing other than what came with distributing the compost. When spring broke, the snow cleared and the ground became workable, I would then add another thin layer of manure compost on top of the mulch plus anything I wanted to add for plant nutrition (often some bonemeal in my case), and maybe a bit of bloodmeal sprinkled over top, then mix and lightly cultivate all of that into the top soil, maybe an inch or two deep being careful and shallow close to plants. After getting the surface raked out as I wanted, I then topped that off with a new layer of mulch for spring/summer. In fall, I started the whole cycle over again. I probably put twice as much mulch on in the fall as in the spring. If you follow that approach you may be surprised how your soil will transform in even a couple of years.

Now a question - what do you know about your soil? Had any tests done?

Depending on where in Canada you are the soil you have is not "fairly heavy with clay" it is clay. You do need to get adequate amounts of organic matter in to that soil and wood chips simply take too long, especially if the soil organic matter is too low for a good active Soil Food Web to be at work. Some recent research also indicates that using wood chips as a mulch on soils with inadequate levels of OM can cause available Nitrogen to be tied up by what soil bacteria are there to process those wood chips.

I would go back to using compost as mulch until such time as there is adequate amounts of OM in that soil.

To the notion that wood chip mulch "ties up" nitrogen in soil, I provide the following from Linda Chalker-Scott of Washington State University (full reference linked below)

Concern: Wood chip mulches will
tie up nitrogen and cause deficiencies in
plants.

Evidence: Actually, many studies
have demonstrated that woody
mulch materials increase nutrient
levels in soils and/or associated plant
foliage. My hypothesis is that a zone
of nitrogen deficiency exists at the
mulch/soil interface, inhibiting weed seed
germination while having no influence
upon established plant roots below
the soil surface. For this reason, it is
inadvisable to use high C:N mulches in
annual beds or vegetable gardens where
the plants of interest do not have deep,
extensive root systems.

As I noted, if incorporated into the soil before they have decomposed, wood chips can divert soil N sources away from plants. That can be dealt with via supplemental N additions along with any un-decomposed wood chips being incorporated into the soil. When applied as a mulch there is absolutely no adverse effect on soil N.

Building soil OM in a permanent planting bed via topdressing with either mulch or compost does take time. My experience in the clay soils in TX is that the use of supplemented wood mulch or compost as a mulch will have comparable effects in approximately the same amount of time. Wood chip mulch of very high quality, aged at least 6 months, is far more readily available and cheaper than comparable amounts of compost, which if purchased is often of very questionable quality.

About the only alternative to topdressing and the time it takes is to remove the plants, amend the soil, then replant.

Here is a link that might be useful: Chalker-Scott on Wood Chip Mulch

This post was edited by TXEB on Sat, Sep 7, 13 at 9:49