getation actually does not reduce
summertime moisture loss any better than mulching with dry soil,
sometimes called "dust mulching." True, while the surface layer
stays moist, water will steadily be wicked up by capillarity and be
evaporated from the soil's surface. If frequent light sprinkling
keeps the surface perpetually moist, subsoil moisture loss can occur
all summer, so unmulched soil could eventually become desiccated
many feet deep. However, capillary movement only happens when soil
is damp. Once even a thin layer of soil has become quite dry it
almost completely prevents any further movement. West of the
Cascades, this happens all by itself in late spring. One hot, sunny
day follows another, and soon the earth's surface seems parched.

Unfortunately, by the time a dusty layer forms, quite a bit of soil
water may have risen from the depths and been lost. The gardener can
significantly reduce spring moisture loss by frequently hoeing weeds
until the top inch or two of earth is dry and powdery. This effort
will probably be necessary in any case, because weeds will germinate
prolifically until the surface layer is sufficiently desiccated. On
the off chance it should rain hard during summer, it is very wise to
again hoe a few times to rapidly restore the dust mulch. If hand
cultivation seems very hard work, I suggest you learn to sharpen
your hoe.

A mulch of dry hay, grass clippings, leaves, and the like will also
retard rapid surface evaporation. Gardeners think mulching prevents
moisture loss better than bare earth because under mulch the soil
stays damp right to the surface. However, dig down 4 to 6 inches
under a dust mulch and the earth is just as damp as under hay. And,
soil moisture studies have proved that overall moisture loss using
vegetation mulch slightly exceeds loss under a dust mulch.

West of the Cascades, the question of which method is superior is a
bit complex, with pros and cons on both sides. Without a long winter
freeze to set populations back, permanent thick mulch quickly breeds
so many slugs, earwhigs, and sowbugs that it cannot be maintained
for more than one year before vegetable gardening becomes very
difficult. Laying down a fairly thin mulch in June after the soil
has warmed up well, raking up what remains of the mulch early the
next spring, and composting it prevents destructive insect
population levels from developing while simultaneously reducing
surface compaction by winter ra