Mulch – It Does a Garden Good


mulchOne of the common differences between long time expert gardeners and those just taking up gardening is the use of mulch. The gardeners who have experience and success over the long term are invariably active ‘mulchers’ while new gardeners tend to fail to incorporate this important practice into their gardening.

Perhaps part of the reason for this lack of mulching by newer gardeners is confusion about how and when and with what, to mulch.

How can one practice accomplish such vastly different (even sometimes polar opposite) tasks and objectives?

The answer lies not only in the techniques and methods of mulching, but also in the materials used for the actual mulch.

Why is mulch so important in the vegetable garden? What are the big advantages of mulch and how can you use mulch effectively without creating more problems for yourself? There are a few basic principles of mulching that make it a lot easier to understand and to choose the most beneficial practices for your own garden.

Mulch – Just What Is It?

Mulch is a layer of material which is laid over the garden bed, between plants, or over the top of the entire garden during fallow seasons. It is distinguished from amendments by the fact that it is not worked into the soil, but sits on top of the soil. Mulch can be made up of a wide variety of materials, depending on the garden conditions you want to address.

Choosing the Right Mulching Materials – Paper, Cardboard, Straw and Plastic for Weed Control, Moisture Retention, or Warming of Garden Beds

Mulching for Weed Control

When dealing with weed control issues, use dense, non-porous and light blocking materials such as newspaper or cardboard. Both of these materials can be available at little or no cost. Consider picking up end rolls from local paper producers, they are free and have no ink whatsoever upon them, so no need to worry about ingredients of ink. For cardboard, cut up boxes received as packaging in the mail or ask local shops for sheet or box cardboard scraps, they are especially helpful in high weed infestation areas and are a very good base for a weed control mulch. Unlike commercially available weed blocker fabrics etc. newspaper and cardboard do not stop the flow of air or water through the garden bed. Over time this will allow them to be completely transparent partners in the assistance of restructuring the living plant relationships in the bed without harming or destroying the active microbial and soil organism life which is crucial to healthy vibrant soil.

Straw retains moisture and creates a thick wet living barrier to scorching sun and hot wind. It also can be a haven for wet weather garden pests like slugs and snails, so it must be used in conjunction with coffee grounds and other top dressings in wet garden conditions.

Plastic is most often used as a temperature elevator in cooler climates. Black plastic can be an effective way to destroy unwanted weeds in pre-gardening beds (heat and no light), it is also useful for extension of garden seasons in fall, keeping soils warmer in cool autumn weather. Clear plastic will have the inverse effect on weed control and can therefore be used to enhance and speed crop growth. Recent research has demonstrated that red plastic mulch increases tomato yields some 20%.

This simple list of examples demonstrates why it is hard to follow generic instructions suggesting that mulch is good for one particular situation (for example, retaining moisture in garden beds during hot weather) unless you know what type of mulch is being used with which crops and in what climate.

When we start by looking at the specific objectives for any mulching project in the garden, it is a lot simpler to determine the best materials and steps needed to accomplish our goal.

Cooling a garden bed, or raising its temperature for earlier Spring planting are both functions which different mulching materials can accomplish; so let’s look at the basics of mulch material composition and properties.

Mulch Material Composition and Properties

The first step in good mulching practice is to identify the result you are seeking, or the multiple results if there is more than one.

Next, consider the materials most easily available in your area. This will depend on local agriculture, forestry or other activities which produce materials that are inexpensive and easily obtainable in your location.

Finally, consider the longer term impact of the mulch you are choosing, and make the best assessment possible of what will work best in the short and long term for your gardening objectives.

Mulching materials: A Sample List

This is not an exclusive or exhaustive list by any means, but gives a good idea of some of the most common mulches and how to think about the qualities of mulching materials.

  • Coffee grounds
  • Grass Clippings
  • Leaves
  • Straw
  • Seaweed
  • Saw Dust
  • Wood Chips
  • Bark Chips
  • Newspaper
  • Cardboard
  • Coir
  • Cocoa Hulls
  • Black Plastic Sheeting
  • Red Plastic Sheeting
  • Burlap (with caveat!)
  • Old Carpet (NOT!)
  • Wool (especially raw sheering, untreated)

Mulching with burlap, old carpet or any porous material can be seriously problematic if your goal is weed control. The weeds simply grow up through the holes in the material and then you have that material firmly affixed to the soil surface by weeds and their roots. This is not a situation you will be happy with.

On the other hand, if your goal is to hold seeds in place during early rains as they sprout, an old burlap sack or strip of burlap can work very well to do this and can be removed as soon as the seeds sprout and before they grow up through the weave of the burlap. This way the seeds will stay in the place they were planted even if heavy rains wash through the bed.

Hot and Dry or Cool and Wet: Two Approaches to Mulching

There are two basic conditions which can be greatly improved by the addition of mulch in the garden.

Mulching for water retention and reduction of soil root zone temperatures in garden beds

The first is extreme heat or drought conditions. High temperatures and little water combine to stress plants in two ways, reducing water retention and heating the root zones of plants. Without mulches, the plants are subjected to drying winds across the soil surface and the direct impact of extreme temperatures from direct sunlight on the soil.

In these conditions, the goal is to increase humidity and decrease temperatures in the soil and in the root zone of the garden. By retaining moisture in the soil surrounding the roots and keeping soil cooler than it would otherwise become if directly exposed to sunlight and drying winds.

Mulching to increase soil temperature for earlier planting or later harvest

The second condition in which mulching can be extremely effective is nearly opposite the first, when cooler, wetter weather impedes plant growth and encourages the growth of fungi and disease, such as powdery mildew. While these conditions may not interfere with the typical cool weather greens or brassicas, they can wreak havoc on warmer summer crops such as tomatoes, peppers, squash or eggplants.

Here the objective is to warm the soil, minimize excess moisture in the soil and provide protection from heavy rain or extremely wet conditions.

Making Appropriate Choices Based on Crops Being Mulched

Another major consideration with mulch is the crop you are mulching. When mulching tomatoes and peppers, the plants are up off the ground as they grow and you can snip back lower leaves to keep them from coming in contact with the garden bed where slugs, insects and diseases can all be transfered to the plants.

When growing vining squashes or pumpkins, this is not the case and it is not really possible to lay down mulch in a pumpkin patch that has already spread over the ground. The mulching goals in the two beds are very different.

Pumpkins provide good moisture retention and shading in their beds with large leaves. They may need increased air circulation to prevent excessive moisture. Overcrowding with weeds or too dense a crop can cause moisture build up leading to diseases and a light dry mulch may enhance air circulation. Weeding and mulching must be performed before the pumpkins spread out to be effective. Weed the pumpkin patch first and mulch it well with newspaper, cardboard or other dense weed controlling material topped with a thin layer of straw, leaves or dry grass clippings. This bed will not require additional mulching once it is established.

Tomatoes will benefit from continual replenishment of mulch layers throughout the growing season to keep the bed cool and moist. Top-dress tomatoes, peppers and eggplants with bone meal, magnesium or compost. Work the amendments into the top two inches of soil around the plants. Top off with fresh mulch of either fine straw, grass clippings, or other moisture retaining mulching materials.

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