In the spirit of "the problem is the solution"--I was trying to see a solution hiding in the massive spruce screen that looms over the south side of my house, casting shade over what would otherwise be prime zone 1 growing real estate, and limiting what would otherwise be welcome winter sunlight.

The trees are approximately 65 years old, and I don't feel that felling them is currently an option--at least not until appropriate deciduous replacements are well established.

I have a set of swings set up between two of these spruce giants for my kids, and have always appreciated how the generous mulch of needles and cones provides a wonderfully thick and spongy fall surface...and so, I decided to experiment with using this abundant source of free material as a mulch around several new plantings this spring.

Initially, I used the spruce-cone mulch in 3 applications:

1) around sheet-mulched cucumbers in an area where quack grass required suppression;

2) around some newly transplanted strawberry plants, salvaged when I edged the lawn around my strawberry patch, and;

3) around some grape cuttings, sheet-mulched and planted directly into the sod in the area around a telephone pole and supporting guy-wire.

...In each case, the mulch-layer was between 5-8cm thick, and a generous quantity of compost was added around both the cucumbers and grape cuttings.

It didn't take long for me to notice a dramatic effect where I had used this spruce-cone mulch.  Not only did it COMPLETELY suppress any weed growth--it appeared to EQUALLY suppress the growth of the plants I had mulched with it!  Strawberries, cucumbers and grape all sat as though is suspended animation--not growing appreciably for nearly a month!  Indeed, it wasn't untill I intervened with dramatic dosings of compost tea that I began to see some growth (and today, the cucumbers, in particular, while late in the season, are THRIVING).

My current theory is either that the spruce mulch contains some sort of negative allelopathic agent--OR--that in SPITE of my generous use of compost, the high carbon and surface-area of the spruce cones combines to monopolize the available nitrogen, effectively starving the adjacent plants--aka "nitrogen drawdown".  (Indeed, the effect was very similar to what I have observed when using fine sawdust as mulch on a pathway.)

So.  Rather than abandoning my plentiful supply of free mulch, I decided to use it more judiciously in PATHWAY-like applications...for instance, around a series of haskap, current, and gooseberries I recently planted.

If the phenomenon is nitrogen drawdown rather than negative allelopathy, then I would expect to see increased fertility in these areas NEXT growing season, following winter decomposition of the spruce cones.  If, on the other hand, it IS some sort of allelopathic effect, then I would expect to see continuing plant suppression in areas where the spruce mulch was used.

I will keep you posted!

-Tim