Mulching Alaska gardens is covering soil surface with materials that smother weeds and delays the evaporation of moisture from your precious Alaska garden soil. Most people may think of Alaska garden mulches as being dead plant material such as spruce needles or bark chips. Anything keeping grass & weeds down and moisture in can be considered an effective mulch (including aluminum foil, plastic sheeting, old carpets, and low-growing non-competitive Alaska plants).

Good Reasons for Mulching Alaska Gardens

Proper mulching almost eliminates the need to pull fast-growing Alaska garden weeds. Only the most tenacious perennials are able to work their way through the best Alaska garden mulch. Mulches prevent weeds seeds from reaching the soil and germinating. Instead, they fall on an often dry surface where they can be eaten by birds or blown away to your neighbors' yards.

Covering soil surface with Alaska mulches reduces the amount of sunlight and wind reaching the soil, so water evaporates from garden soil more slowly. Soil stays cooler, so the roots stay cooler, which may not be what you want. One trick to to place clear plastic over the area after all snow is gone to quickly warm up the soil, else plants my be a couple weeks behind other Alaskan plants without mulch.

Mulch derived from plants (such as grass clippings, leaves or shredded stumps, limbs & bark) can also add organic matter to the soil, improving its structure and fertility and encouraging a healthy population of microorganisms.

Finally, mulches make a garden more attractive, especially a new one where the plants have yet to fill in. And when it rains, a mulch keeps soil from splashing onto the leaves or nearby paved surfaces or buildings.

Caution about Alaskan Garden Mulches

Mulches have some drawbacks. Insects such as slugs and earwigs love moist shady hiding places Alaska garden mulch provides. If insects are abundant enough to cause serious damage, you need to remove mulch from your Alaskan garden until you get things under control. One tip is to compost the mulch with fresh grass-clippings and water. Heat this up in a pile greater than three feet in diameter to acquire critical mass for the composting process to work. Turn the pile every week and add water. Heating the compost pile will kill all weed seeds and insects that ended up in your great Alaska mulch.

Organic mulches also cause a temporary boom in the population of Alaska soil microorganisms, which can tie up some soil nutrients. This boom is especially a problem with mulches high in carbon, such as wood chips. To compensate, fertilize first with a high-nitrogen fertilizer such as rotted manure or bloodmeal or high-nittrogen lawn fertilizer. Or put a high-carbon mulch on top of a layer of balanced mulch, such as grass clippings or compost. You can add nitrogen, phosphorus, and (in alkaline soils) sulfur to make sure there's enough left for the plants.

Choosing and Using Best Alaska Garden Mulches

When choosing mulch for your Alaska garden, consider how long you want it to last, how attractive you want it to be, what's available, and how much you want to spend. We like to go to the Anchorage woodlot on C Street and 100th to pick up free wood chips. I prefer them with plenty of leaves when I compost, otherwise, I want clean chips with no leafy matter. Often the chips have started composting because the chips have many cottonwood or birch leaves attached to the chipped branches homeowners bring to the Anchorage, Alaska woodlot.

Bigger pieces of mulch last longest. Soil organisms can digest a blade of clipped grass pretty quickly, but might need a year or two to chomp through a spruce or cottonwood bark nugget. And juicy materials, like compost, deteriorate faster than woody ones, like newspaper. So if you want a long-lasting mulch, as you might around trees and shrubs, choose bark nuggets or another big, woody material. If you want a mulch that deteriorates in a season, as you might to improve the soil in a vegetable garden, go with something small and juicy like grass clippings or leaves.

Whatever material you choose, you want to apply it deeply enough to control the toughest Alaska garden weeds, but not so deep that it smothers the roots of your Alaska garden plants. How deep that is depends on the plant, how dense the mulch is, and how well aerated yoru garden soil is. Start by putting a 1-2 inch mulch around flowers and vegetables and a 4-6 inch mulch around trees and shrubs. If weeds pop through, add another inch. As the mulch breaks down, add more.

Final considerations are how easy Alaska garden mulches are to find and how much they cost. Some mulches, such as newspaper and grass clippings, are easy to come by and inexpensive. Others, like bark mulch, are also easy to come by but cost a few bucks a bag.

Some Common Alaska Garden Mulching Materials

Bark chunks

Sometimes called nuggets on bags in stores, may be attractive pieces of bark about three inches in diameter. Bark chunks last a long time (years in some climates), because they're so large and woody. Of the various sizes of bark mulches, bark chunks are the best garden mulch for weed control. Bark chunks are so coarse textured that they don't encourage a big growth spurt in the soil microorganism population that can tie up soil nutrients. If you don't turn your garden soil each year, you can reuse the same mulch by scraping it aside, planting new plants such as brocolli or cabbages, and replace the mulch. Many gardeners realize the benefits of not disturbing Alaska garden soil unless necessary during the planting season.

Bark chunks' slow decomposition means you'll have to put finer organic materials under them if you want to improve the soil; try grass thatch or compost. I never use manure because of weeds. Because the bulky pieces decay slowly, don't turn them under the soil, where they can create air pockets near plant roots.

How to Use: Alaska bark chunks provide good ornamental mulch for trees and shrubs, or for covering the spaces between plants in a new planting. Spread to a depth of about 3-4 inches. In a new strawberry bed, we place them about one inch deep to conserve moisture and prevent weeds.

Wood chips

Small pieces of wood about an inch in diameter. Wood chips make decorative mulch that breaks down faster than bark chunks. Wood chips add more organic matter to Alaska garden soils. Wood chips are high in carbon, making soil organisms tie up nitrogen and other soil nutrients as they work to digest the chips. Bags labeled "wood chips" can contain wood other than bark, including leftovers from the timber industry. Small chips may bounce onto sidewalks and lawns during Alaska wind storms.

How to Use: Spread to a depth of about 3-4 inches around trees and shrubs, or in the spaces between plants in a new Alaska garden planting.

Shredded Bark

Contains narrow strips of bark a few inches long. Shredded bark breaks down faster than nuggets or chips, so you can turn them into Alaska garden soils after a year or two as a source of organic matter. Shredded bark costs less than bark chunks. Shredded bark is high in carbon, so soil microorganisms draw nitrogen and other nutrients from the soil supply as they break the bark down. Shredded bark can fly out of Alaska plant beds in wind storms. Shredded bark may be less effective for smothering Alaska garden weeds than bark chunks.

How to Use: Spread a 4-inch layer around trees, shrubs, and flowers.

Compost

Provides fertile mulch you can make. Compost provides ideal soil-building mulch for vegetable gardens or flower beds that you plan to turn under. Fully decomposed & screened mulch is too fine to smother aggressive Alaska garden weeds. Partially decomposed compost is bulkier and better at controlling weeds, but may trigger a burst of activity in soil organisms that temporarily ties up nitrogen. Compensate this by adding a little bloodmeal or other source of nitrogen.

How to Use: Apply at 2-4 inch layer around Alaska vegetables, annuals and perennial flowers, keeping fresh compost about an inch from the stems to prevent rot.

Hay and Straw are loose mulches, so they don't block air flow to the roots of plants. Both are good winter mulches for roses, strawberries, and other perennials, but may not be easy to acquire in Alaska. Alfalfa hay contains more nitrogen than many bark mulches, so its decomposition doesn't tie up soil nutrients. Hay can contain weed seeds, so I never use it until I compost it thoroughly. Straw is usually free of weed seed and is often used to keep newly seeded lawns moist between waterings. Straw lasts longer than hay, but is woody enough to make soil organisms tie up nutrients, so add a little bloodmeal or other nitrogen source. Because neither is a dense mulch, weeds can pop through it.

How to Use: Apply in a 4-6 inch layer.

Shredded leaves

Provide lightweight, insulating mulch well suited to protecting roses and other woody perennials during the winter. Although you can buy shredders, your lawn mower is probably the best shredding tool around. Rake the leaves into along, low pile and run the mower over it, catching the leaves in a bag.

How to Use: Apply is a 4-6 inch layer.

Grass clippings

Add great organic matter to the soil. Because grass clipping have a good balance of carbon and nitrogen, they don't make soil organisms tie up soil nitrogen. Fresh clippings sometimes get moldy and smelly. Because the clippings break down quickly, you have to replenish them often. Grass that's gone to seed or contains weed seeds can create a weed problem in the garden.

How to Use: If you're applying fresh clippings, add a thin layer (1-2 inches). Use 2-4 inches of dried clippings. Replenish as necessary.

Leaf mold

Composted leaves with no other material. Leaf mold makes a great Alaska humus rich in micronutrients. Because leaf mold has had time to decompose, its ratio of carbon to nitrogen is more favorable than fresh leaves. When added to Alaska garden soil surface as a mulch, it adds organic matter to soil. It can take several years for dry leaves to decompose into leaf mold.

How to Use: Shred the leaves first by raking them into piles and running the lawn mower over them. Then dump the shredded leaves in a pile; you may want to build a wire bin to contain them. To make the leaves break down quicker, keep them moist and fluff them with a pitch fork every month or so. The leaf mold is ready when its soft and crumbly. Add up to four inches to the soil surface as a mulch.

Sawdust

Adds organic matter, helps lower the pH of alkaline soils, and repels some insects. Sawdust is so high in carbon that you'll need to add extra nitrogen, unless you compost it.

How to Use: It's a good idea to compost sawdust before adding it to the soil surface, both to lower the carbon-to-nitrogen ratio and to give any toxic substances in the wood a chance to leach out. Then spread 1-2 inches on the soil surface. You can turn it under at the end of the season.

Newspaper sheets

Provides barrier that weeds have a tough time breaking but water can easily pass through. Newspaper breaks down over time, adding organic matter to the soil. Newspaper is inexpensive and readily available. If it's too thin, it won't last as long as you want and weeds will pop up. Too thick, and you'll have to pull it up at the end of the season if you want to turn the soil or add fertilizer. How rainy the season is affects how long the paper lasts. Newspaper is high in carbon, so if you work it into the soil after it disintegrates you'll need to add extra nitrogen.

How to Use: Lay sheets of paper on the soil surface and weight them with grass clippings, stones, or some other material to keep them from blowing away. Try making the layer 10 sections thick to start with; reapply if the layer breaks down before the season ends. Don't use colored sections of the newspaper, which may contain toxic dyes.