On March 5
th I attended a workshop
sponsored by the Carolina Botanical
Garden: Soil is All. I share some information below
that appears relevant to our garden.
Some of the practices discussed, such as soil testing and amending
already being applied to our garden. The
presenters stressed the importance of humus/organic matter in soil, which
provides space for air and improves water retention. Compost is the ideal way
to add organic matter to soil because good quality compost improves the
chemical, physical, and biological characteristics of the soil. Other, more
readily available, sources of organic mater, such as leaves and saw dust,
improve primarily the physical characteristics of soil (see
Building
Soil with organic amendments.)
The complex components of soil ecosystems were explained briefly. Topsoil and
soil that supports growth is alive with both visible (worms, larvae and insects)
and invisible organisms. Micro-organisms, especially the fungi, mycorrhizae* are
essential for healthy plant growth. The interaction between certain fungi,
mycorrhizae, and plant roots benefits both (symbiosis) and helps the plants
absorb nutrients and resist disease
http://aggie-horticulture.tamu.edu/faculty/davies/research/mycorrhizae.html.
Planting cover crops, especially legumes, helps maintain healthy
mycorrhizal populations . Tilling and leaving soil bare disrupts
this beneficial soil ecosystem.
In addition to cover crops, and intensive planting, the workshop demonstrated
and recommended use of mulch to cover bare soil. Placing mulch over the soil
protects against soil erosion, suppresses weeds, stabilizes soil temperature,
reduces water loss from evaporation, and creates a barrier between plants and
soil-borne diseases.
All mulches block sunlight, so prevent
seeds already present in the soil below from sprouting. Compost can be used as
a mulch, but allows wind-borne weeds to grow vigorously. In contrast, other
mulches, such as landscape cloth, newspaper, or a thick layer of leaves, grass
clippings, straw or wood chips, usually don’t provide the conditions that wind-borne
seeds need to sprout.
At the UNC Campus
Community Garden
a thick cover of leaves is used for mulch. Sometimes mulch is placed around
small plants. Alternatively, existing mulch can be cut or moved aside to place
transplants or seeds.
Many mulch materials decompose, adding organic mater to the soil, and must be
replaced yearly. The book that is our primary gardening guide, Weedless
Gardening, by Lee Reich, provides a mulch guide (page 24-25) and recommends
adding mulch whenever bare soil is visible (page 48). Currently, some of our
beds are mulched with decomposing cover crops, but bare soil abounds. In the
future, we should consider how best to apply mulch to our garden.
-- Kris Weigle
