Don't confuse mulch, composting

Today’s Weekend Gardener (and next week, too) will look at mulch and compost and their differences, beginning with mulch.

Mulch is a layer of material, preferably organic, placed on the soil surface. Gardeners often use it after planting to hold down weeds, retain moisture, and for winter protection. The first use is not necessarily wise (we’ll explain why); the second and third are definitely viable ones — necessary in our often harsh North Idaho summers and winters.

Some people think bare soil between vegetables means better growth due to lack of competition from weeds. They don’t realize that bacterial action, which breaks down organic matter into plant food, slows down to almost a halt in the dry surface of the soil, where most of the plant’s roots compete for water and food.

Keeping the soil moist promotes the action of bacteria as well as water for the plants.

By removing the weeds, nutrients and plant matter that could be given to the soil bacteria as food are taken away — plus the exposed surface gives nothing for bacteria to work on. Watering bare soil also tends to push the dirt around, disturbing surface rootlets and causing soil caking.

Proper mulching is a method of gardening that lets the water trickle down to the soil — perhaps even reducing the need for watering.

Mulches of old plant matter, applied thickly, helps keep down weeds considerably, while providing nourishment. However, some vegetables need a thoroughly warmed soil to encourage ideal growth. A mulch applied too early in the spring, before ground temperatures have had a chance to climb a little, may slow up such crops.

Once plants are well started, though, mulch is definitely in order. The amount that does the job for you, your soil and your plants takes some experimenting with various materials and depths.

The big secret, however, is to use prepared or already “digestible” mulch. These include grass clippings which are rich in nitrogen, leaves, an abundant source of humus and minerals including calcium and magnesium as well as nitrogen, phosphorus, and potassium (they are especially valuable around acid-loving plants.

Another “quickie” is paper, particularly old newspapers (not the shiny, heavy sheets), for newspapers have excellent moisture-retaining qualities (as well as weed control) and can be laid out in the vegetables garden and nursery.

Water well, then cover if you wish with straw, wood chips or simply rocks on the corners to hold in place till decomposition begins. Straw, clean and easy to lay down, is slower to decompose, so is best in the rows between plants until fall, when it can be tilled into the soil for over-winter enrichment.

Caution: Mulch purchased by the truckload is often quite dry, and if applied in any depth over three to four inches, must be dug into the soil where it is used. If it is not, the natural barrier existing between the soil and the mulch keeps water from reaching the soil; it simply soaks through the mulch and drains away over the soil instead of into it.

Therefore, when applying this type of mulch (generally peat mixtures), make sure to leave plenty of space around shrubs, trees and ornamentals in the landscape to make sure they receive enough water.

If over-mulching has happened in your landscape and you can’t possibly “dig in” the large amount of mulch, take a long-tined garden fork or pitchfork and shove it in and out throughout the garden to make drainage holes; this is a big job, but easier on you than digging and turning copious amounts of soil. Just make sure the tines reach into the soil layer two or three inches and be generous in your poking (think pie-crust) — stabbing every six inches apart.

(Editor’s note: For many years, Valle Novak has written gardening and cooking columns for the Daily Bee. “Weekend Gardener” and “Country Chef” became renowned for their humor, information and common sense advice on how to do everything from planting to cooking. While she recently retired, she has shared a number of columns to delight her many fans. This is one such column, originally published on July 22, 2007.)