When the summer heat arrives we commonly find ourselves dragging hoses and sprinkler
heads. Sometimes we are fooled by the periodic showers of a pop-up thunderstorm and think
that enough rain has fallen to give the plants a good drink. This mistake leaves us frantically
trying to save scorched plants a couple of days later when the heat rolls back in. Instead of
resurrecting the drought stricken plants, plan now to combat the periodic dry spells by mulching.
First, there is no substitute for good soil structure, including plenty of water-holding
organic material incorporated into our Midwest clay soils. However, if you have a garden which
was not well prepared or the organic matter has decomposed to the point of being no longer
functional, mulching the soil surface around plants is a prime consideration in reducing water
shortages. Besides providing an insulating layer to moisture loss, mulch lowers the soil
temperature, retards weed growth, leaches some nutrients into the soil and enhances the garden
Traditionally, we think of mulch as some organic plant material. However, during the
last 20 years, an assortment of plastic films, fabrics and mats have become available to serve a
purpose similar to that of organic mulch. In the 1970s, plastic sheets were the only alternative to
organic mulch. Along with being inexpensive and readily available, plastic films help to control
soil temperature and exclude weeds by blocking sunlight. Covered by a layer of organic mulch
to avoid the deteriorating effects of ultra violet light on plastic, these films work quite well for
vegetable gardens. A drawback, however, is that plastic mulches exclude rainfall and reduce air
aeration necessary for root growth.
Poorly drained soils may become anaerobic promoting methane gas production from rotting
organic matter which is harmful to root development and encourage fungal root rots. Plastic
mulches should be removed at the end of each year. Mistakenly, they are often used under trees.
As a result, the tree roots grow up to the surface of the soil just beneath the plastic. This is not
desirable for long term tree health, and it also makes them more drought susceptible.
In the 1980s, plastic mulches were replaced with landscape fabrics which allow air and
water through, yet block light and most weed growth. This mulch material presents a vast
improvement over plastic mulching materials. When combined with a top dressing of pine
needles, landscape fabrics can be aesthetically pleasing, durable and give good weed control.
Care should be taken to remove weeds as they germinate in the mulch. Weeds will anchor down
the fabric and when pulled, might tear the material.
While synthetic materials are easy to find and use, organic materials have the added
advantage of improving aeration and water holding capacity as they degrade into the root zone.
Included here is hardwood or pine bark, wood chips, pine needles, sawdust, grass clippings,
straw, composted leaves and newspaper, to name a few. All have some pros and cons. Shredded
bark and wood chips are particularly popular because of their attractive appearance and durability
for more than one season. Pine needles may not be readily available, but have superior effect on
weed control due to their inherent acidity. Wood chips, sawdust and grass clippings degrade
more quickly and may deplete soil surface nitrogen as they decompose. Herbicide-free grass
clippings should be spread in a thin layer of 1 inch or less. Straw and leaves are excellent
insulators and are generally readily available. Leaves should be mostly decomposed or shredded
before spreading to avoid being blown away.
While most landscapes mulched with straw might be unattractive, a 6-inch layer of straw
works in well with vegetable gardens. The same is true for newspaper which can be very
effective in vegetable garden weed control. However, as with leaves, a layer of top mulch should
be applied to avoid the paper from blowing. Whether you choose synthetic or organic methods,
mulching is a wise garden practice with numerous benefits.