We all appreciate the aesthetic value of a nice mulch in a garden bed, but there are far more important reasons for adding a layer as the temperatures begin to drop.
One of the most obvious reasons is related to the chilly winter ahead, in soil temperature retention. Many Canadian perennials are fairly hardy and will survive the deep freeze, but many won’t. Especially if it’s the first year for the plant or if it was recently transplanted from another location. It keeps the soil around your plants’ roots cooler on warm days and warmer on cold nights. This is especially important during rapid temperature shifts, or in the case of dry but cold winter. Snow will serve as an insulator as well but in the absence of snow your plants need some where to hide.
Weed control is another critical reason to get mulching. It never ceases to amaze me that when nothing else is growing weeds find a way to creep into my garden. Keep in mind it needs to be a thick layer to ensure that any existing weed seeds never get the chance to germinate. Ensure as well that the mulch itself is weed free, as you can expect its a little counterproductive to spread weed filled mulch or hay.
You mus’ add humus. (ha ha) But seriously a benefit of an autumn mulch is the fact that the summer’s mulch layer beneath will continue to breakdown. Humus is basically the by-product of organic decomposition and will act as both a fertilizer and a giant sponge for moisture retention, the perfect start for next year’s
Keeping everything in its place is another handy result of a good fall cover. A heavy layer will help reduce frost heave. Frost heave occurs when there is rapid, frequent changes between the freezing and thawing temperatures. This causes the ground to expand and contract and in it’s wake affectively heaving perennials and other plants out of the ground.
You can also mulch up, wrapping small juvenile trees by creating a frame in a square around the tree with wooden stakes. Once the ground has frozen wrap the frame with burlap and fill the area around the tree with mulch. This is especially important with tender trees such as Japanese maples and certain standards. In late March or early April (depending on the status of snow) simply snip away the burlap and allow the mulch to spill around the base of the tree.