When digging a garden is like baking bread
Reader S.U. emailed recently to ask:
I just moved into a condo and have very little space and
there is almost nothing worth keeping planted here now. I would
like to know if it is too early too start to try to loosen or till the very hard clay that surrounds the
base of my house all the way around.
We work soil any time that the excess water's drained from it.
It's not a calendar date because some places thaw and drain more quickly in spring or have more
trees drawing water from within. Some get wet in summer. Sandy soil
typically warms and drains more quickly in spring than clay, but
sand on top of a poorly drained subsoil can stay wet weeks longer
in spring than well drained clay, and be wet off and on all
So do the squeeze test.
It's described above, right. Do it before you work any bed.
Don't expect anything that's hard packed to become fluffy loam
overnight. Do expect it to become better during one growing season
if you introduce air and organic matter (compost or leaves work
well). The soil and beds you see here all grew well their first
year and had significantly better tilth by year end.
Then aim to add air and organic matter to that soil.
We often do no more to hard packed soil than to pop it up in big
clods, leave it rough and spread a layer of compost over it, then
mulch. The compost fills the spaces and the mulch becomes the
smooth surface we humans love. (Nope, plants don't have to have
"smooth.") Plants' roots love a clod-compost bed, and love the
nutrient-rich, moisture retentive clay too. Meanwhile, moisture and
organic life go right to work on the clods' exposed surfaces,
crumbling and remixing the particles.
Drainage in gardening is not about how water runs along a
surface and out to a storm drain! It's about how well the water
falls into and through the soil. Most garden and landscape plants
grow well only where the soil is well drained -- where excess water
falls through soil within a day, drawing air in to take its
Right: We broke up this hard-packed loam and added compost
in fall. We planted trees and shrubs there right away -- easier to
plant big balls than small pots in such a lumpy bed; the perennials
could wait until spring! By spring the plants had 18" of roots out
in all directions through the compost-filled channels and myriad
tiny roots forming webs around those rich clay chunks.
Below: This 18" deep hole had better drain completely in 12
to 24 hours or we'll need to make a raised bed. If 6" of water is
left in the hole after 12-24 hours, we'll raise the bed 6". Then,
plants' roots will be up out of the soggy soil that will be there
after every rain or watering.
Clay? Maybe. Even sand can
be hard packed
Many people call a soil clay simply because it's hard packed.
Yet this is sandy loam that was worked with machinery when it was
still wet in spring. Being pressed and whipped with all that water
destroyed the delicate connections between particles that made the
soil crumbly. It collapsed into a brick just like over-kneaded
dough or badly beaten batter would turn into rock hard bread or
Retire that rototiller
If you use a rototiller do it only to make the first break into
tough soil or to turn under amendments lightly, like "folding" in
ingredients into a batter. Don't go over and over a bed to make it
smooth or you can ruin the soil's tilth.
It's especially bad to till soil that has enough clay in it to
feel sticky or slippery. The rotating tines of an 8hp tiller beat
DOWN on the soil below their rotation with (surprise!) eight horse
power. That can pack the subsoil so hard that water backs up into
the bed, ruining drainage by creating a perched water table.