Friday, April 17, 2009

Much Ado About Mulch

Spring rains and light snows have given the weeds a serious head start in the garden this year. If pulling weeds is not your idea of a fun activity, but you just can't give up your vegetables and flowers, mulch is your best friend. Just remember to weed before using it.

Mulch can provide many different functions, and the type you use can determine how effective it is for your yard. It:

*Blocks weeds when laid sufficiently deep

*Keeps the soil cooler in summer, slowing evaporation, and warmer in winter.

*Slows or prevents erosion

*Protects plants from soil-borne diseases that can be splashed up during watering.

*Mulched plants have healthier, more complex root systems

*Prevents crusting of the soil surface, so water will soak in more effectively instead of beading up and rolling off

*Organic mulches break down over time improving soil structure and adding nutrients to the soil

Organic mulches include:

Grass clippings--these are best left on the grass when you mow using a mulching mower if you have a choice. If you have too many to leave down, or if you have access to extras from someone who bags theirs, they can be used around plants. They should be placed after they have had time to dry a bit to prevent matting, which will cause water to shed instead of allowing it to soak in. Always make sure the grass clipping have not been treated with an herbicide in the past two weeks if you are going to use it around your flowers and trees.

Straw or hay--hay has a lot of seeds in it, and should not be used, but straw can be a great mulch. Straw is not very pretty, so it may be best to use it on vegetable beds or on new grass seed. It decomposes quickly and will improve the soil.

Newspaper--makes a great mulch--and it's free! Use several layers thick and then lay a prettier mulch on top to keep it from blowing away. Applied thick enough, it will keep almost any weed at bay for a couple of years. Over time it will break down into the soil, helping the condition and adding nutrients. Most newspapers now use vegetable-based inks in their printing, which are perfectly safe to use on vegetable gardens. If you have any question, call whomever prints your paper and find out. Slick ads or fliers printed with toner should never be put on edibles, and slick ads or magazine pages shouldn't be used in compost or gardening at all as the chemicals on them cause mildew and can leach into the soil.

Pine needles--a two-inch layer makes an attractive covering and allows water to pass through easily. There is a theory that it makes the ground more acidic and should be used around acid-loving plants (which would be a bonus in Utah as most of use have extremely alkali soil.) However, studies have been done that shows they don't make soil more acidic, so I wouldn't count on it.

Wood chips--Large wood chips can be placed up to four inches deep, smaller ones and shredded bark should be no more than two inches deep so it doesn't prevent penetration of water to the soil. Smaller pieces decompose more quickly too, which can tie up nitrogen in the soil so an extra shot of fertilizer is a good idea.

Leaves--should be shredded to prevent them blowing away. You can use a lawn mower to shred them coarsely. Finely shredded leaves tend to mat instead of allowing water through. The advantage of leaves is they look nice, are readily available, and improve the soil quality over time. Apply two to three inches to start. As they decompose you can dig them into the ground and add a new layer, or simply add more to the top.

Live ground cover--Have you ever thought of using plants as mulch? There are lots of great ground covers out there that will block weeds and allow passage of water to the soil. Things like Ivy and periwinkle, among other perennial ground covers, do a great job at this. The only caveat is to be aware that many perennial ground covers are invasive (ivy and periwinkle have been known to attempt garden domination if not restrained).

Inorganic mulches include:

Plastic sheeting--black plastic heats the soil, which can allow you to get your garden beds ready to plant earlier. It keeps evaporation down, which is a plus and minus. In a well-draining area, this isn't a problem, but in gardens with clay soil, this can cause root rot. Black plastic will disintegrate quickly in the sunlight and should be mulched over. Clear plastic will not block sunlight, therefore may increase the number of weeds in the garden unless covered with a good layer of other mulching materials. Holes may sometimes have to be poked to allow water to pass through plastic.

Landscape fabric--does a good job at blocking weeds, and because it is woven it allows water and water to pass through it. It can decompose rapidly if exposed to air, needs to be fastened down to prevent perennial weeds from pushing it up, and the cost can be kind of high, but it is a great solution to a perennial planting area, such as around trees where you don't intend to use annuals.

Rocks or pebbles--can block sunlight to keep weeds down, but won't block stubborn ones like the weedy morning glory. It can be purchased in many colors, but heats up under summer sun. It is also hard to get rid of once you've put it down, so it is best for permanent plantings. I'm going to be mulching paths in my garden with landscape fabric and rocks to keep weeds down this summer.

Ground rubber tires--This is a relatively new option. They don't decompose, so they never have to be replaced, but the effectiveness is still being studied. I wouldn't use this on any edibles, just in case it leached chemicals into the soil, but it could be an attractive mulch for perennial borders and beds, especially if your yard is shady. I would be concerned about sun heating this up too much as it does with rocks in hot, sunny areas.

A few tips: Mulch should not be placed within three inches of plant stems or trunks to prevent decay caused by wet mulch. The extra space will also lessen rodent damage. Wood mulches should not be used against house foundations, as it can provide a bridge for termites, so six to twelve inches of room should be planned in.

If a mulch smells like vinegar, sulfur, ammonia, or silage, it can be toxic to plants and possible kill them. If you are buying new mulch, or if you have a pile, it needs to be turned regularly if it is larger than 4 feet in diameter to prevent 'souring' of the mulch.

Spores from wood mulches can give fungus a place to live, so in wet areas (or yards that get watered really frequently) it should not be placed near houses or cars. One solution to this is to spread pine needles over existing hardwood mulches to prevent black spots from appearing on your home.

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1 comment:

Cindy Beck said...

Thank you very "mulch" for the great info! :)