I used mine within the same year it was cut and chipped. In fact, the leaves were still green in it when I put down the first lot. There is no problem as long as it is used on top of the soil for a mulch. If it is worked in, it will tie up nitrogen while it goes through the process of breaking down. Note that it is "tied up," not used up. Once the plant matter has gone through the process of aging and composting in the soil, the nitrogen is released again. In this case it was used for flower beds as mulch. Not sure that would chips would break up enought over winter to use in the garden.

But, when we get the urge to work some straight sawdust into the garden in the fall, we just toss on some high nitrogen fertilizer to help break it down into good organic humus that will greatly improve the tilth of the soil for spring planting. Best of both is to find some sawdust bedding from a horse stall. For us it isn't either/or when it comes to organics versus chemical...we use both to get the results we want. If we could find enough organics, we would prefer to use nothing else, but since we can't always do that, this works fine. By the way, covering the garden with leaves, sawdust, blood meal, bone meal, rock dust, etc., and tilling it in every fall used to be called sheet composting. I don't know how early you would have to do it in the northern part of the country, but we have enough soil warmth left over to do at least a part of the garden every year and if you rotate crops, you can get it all at least every other year. Fall crops never cover even half of the garden.

So far - so good for mine that I got earier this spring from a tree service. I had a large load of wood chips delivered and dumped in my back yard absolutely free. The place I found was nice enough to let me know what kinds of trees they would be cutting that day so I would know what would be in the mixture. I've been mulching with it all summer. If there are already weeds where I need to mulch, I cover them up with several layers of newspaper then put the mulch on top of that. I do try to keep the woodchips away from the base of the plants a little bit.
There wasn't any leaves in mine because the trees weren't leafed out yet when they were cut.

Nancy....JUMP on that stuff....as well as leaves, pine needles, etc. It's all great for the soil. After Hurricane Ivan we used a chipper/shedder for our down trees. Put all that tree material back in the gardens. Yes, it takes a bit for it to break down but I found it keeps the flower beds protected and they retain the water better. As it turned out my flowers have done great with that extra moisture. I tend to look at all that "free" mulch out there as part of mother's nature recycling process. And the best part is it's FREE!

Pam

Oh, I forgot to mention that two of the 5 trees we had taken down were walnuts. We took the logs to the mill for lumber, but all the tops were chipped, including leaves and immature nuts. Plants all look fine...no signs of trouble. I was fairly sure it would be fine as a mulch, but must admit I held my breath a bit on that one. ;O)

Walnut has some alleopathic properties, but I don't know if this sticks around after they are cut and chipped. Alleopathic means that the plant can suppress other plants growing nearby. It might be only in the roots. Does anybody know which? Some other alleopathic plants are Tree of Heaven, and spotted knapweed.
I'd like to make sure there's no poison ivy growing on any of these trees. The oils can persist for a long time. However, it seems like a great way to recycle and get a great benefit for your beds and garden.