Hi, I have been 4 years in my current home, and the back garden pretty
much each year needs some new plants and shrubs. Although I admit we
have in the past bought what looks nice and arent necessarily suited for
our east facing heavy clay moisture retaining soil.
Firstly, I have over the last 2 months or so being contemplating
removing the soil/clay from our flower bed about a foot or so and
replacing with new soil mixed in with sand but adding more depth - so
allowing for a total of 15 inches of decent soil to replace the harsh
stuff we have now. Lots of digging out and replacing.....good idea?
As an aside, we had our lawn put down 2 years ago, and only now over the
last month or two with some sunshine and lots of rain has it come back
to life as it were....was previously, quite thinned out especially when
cut and not really great looking - although fine when it looks like it
needs cutting, again due to the clay soil and poor drainage - but I do
throw down aftercut lawn care every so often when I mow it.
In terms of going forward and planting, what types of shrubs, plants,
flowers that are all year round, and keep coming back are best suited
for the environment I describe?
Thanks for the advice and recommendations in advance!!
It is a quick fix that will work as long as you don't create a pond. The
area that you excavate must not go down into the clay or the plants (unless
bog-adapted) will drown. Either cut away enough so that the whole area
drains or build it up into a mound to get the same result. It may be more
effective to make sides for a raised bed depending on the lie of the land.
You have to take levels to work this out not guess.
Unless you need a soft playing surface consider a ground cover that requires
less sun and attention. If keeping the grass try to amend the soil in situ
by applying clay breaker, top dressing and using a mulching blade on your
mower and leave the cuttings there.
What you propose will create an interface between top soil and subsoil.
Many plant roots will not cross that interface.
Instead, start by applying a generous amount of gypsum (calcium sulfate)
to the area. (I don't know about its availability in England, but I can
buy a 50 pound sack for US$9.) Water it lightly. If you don't get any
rain, water it again more heavily in about 3-5 days. Repeat rinsing the
gypsum into the soil ever 3-5 days if there is no rain. Gypsum will
dissolve and react with the clay to make it somewhat granular and porous.
After all the gypsum has disolved and rinsed into the soil, allow the
soil to dry for about a week. It should be moist in the top foot but
not wet. You might have to cover the area with a tarp while rain falls;
remove the tarp as soon as the rain ends so that the soil can continue
When the soil is moist but not wet, apply your purchased top soil to a
depth of not more than a foot. Also broadcast a modest amount bonemeal
or superphosphate over the area. Using a motorized tiller, till to a
depth of 2 feet; this should result in an area more than a foot higher
than it had been (1 foot of top soil plus 1 foot of stirred natural soil
plus some air). You might want to hire a service to do the tilling, in
which case you will not hurt your back and you will not be liable if a
tiller blade breaks.
You will now have a 2-foot depth of well-prepared soil for planting.
Avoid walking across the area when it is really wet; otherwise, you will
undo much of the tilling.
Dress the area with more gypsum annually, about a month before the most
rainy part of the year. You will only have to wet down the gypsum and
allow the rain to rinse it into the soil. Roots will not find an
interface and will thus penetrate into the clay subsoil. With an annual
application of gypsum, nutrients added to the area will eventually leach
down into the clay, except for phosphorus. Phosphorus (bonemeal or
superphosphate) does not dissolve easily and must be placed where roots
will find it, which is why you apply that before tilling.
Since I am not familiar with your climate, I cannot comment on lawn care
or recommend plants for you.
David E. Ross
Climate: California Mediterranean, see
How are you going to remove the barrier 15in or more down, how deep does the
clay have to be amended, how will you know when you have done it and how
long will that take? Maybe the answer instead is not to use deep rooted
plants or to build up mounds several feet high.
If the clay is treated with gypsum to make it more porous and if the top
foot of clay is tilled with new top soil, the interface between the top
soil and the clay subsoil will be blurred. Clay is often rich in
nutrients other than nitrogen. With careful use of fertilizer and with
infrequent but deep watering, plant roots will grow down below that
blurred interface into the clay.
My natural soil is heavy adobe clay. What I have suggested here is
based on my experience, especially my use of gypsum. Every year, I use
at least 50 pounds (23 kg) of gypsum in my garden; some years, I use 150
pounds (70 kg). Other than the obstructions caused by tree roots, I can
dig the soil quite easily; and my plants -- all perennials, shrubs, and
trees -- seem to thrive.
No, I do not have a large garden. My total lot is slightly less than
0.25 acre (0.1 hectare), including the footprint of my house and the
extreme slope that I describe at
David E. Ross
Climate: California Mediterranean, see
Yes, it can still be a problem. For instance, all the fertilizers and
all the minerals in your water that you dump
on the flower bed over the years -- the remains -- may become more
concentrated because they can't move past that X inches of "good soil",
and then you get plants in a saline soil, which collapsse and die.
What you're proposing makes a sort of giant flower pot. With a real
flower pot, you can tip it over at the end of a season, dump out the old
and replace the soil fairly readily. That's a whole lot more work with
a bed in the garden -- as much or more than you started the project with.
is a micrograph of clay particles;
they are flat plates that tend to want to stack or shingle over each other,
forming water-impenetrable layers, particularly if there's enough sodium
in the soil or in what you add.
Treat clay soils with respect... they're difficult to grow on.
A commonly held and vastly mistaken view, IMHO. Difficult to work
maybe. But they are not difficult to grow on at all, if you keep to a
couple of simple rules. Firstly, never try to plant anything when they
are soaking wet. Secondly, never try to plant anything when they are
bone dry. Clay is far more suited to growing many plants than sandy
soil; even those naturally found in sandy environments will often more
than just tolerate clay. I have grown heathers without problem, and
grown and fruited blueberries on clay (pH 6 - 6.5). I have even been
able to move plants which are said to really dislike being moved because
a great lump of clay sticks to the roots, and, to all intents and
purposes, the roots really haven't been disturbed at all. Try that with
sandy or even "highly desirable" loamy soil. The one plant I have given
up with on clay soil is grass. Where it is constantly wet, a lawn
simply ends up a mess, often with more moss than grass. The previous
owner of the house I moved in to had so much trouble he installed land
drains, but even those couldn't make a meaningful difference and in the
end I had the lawn removed (no great loss as I can't stand lawns anyway).
I live in the Sussex weald, and have been gardening on clay for over 25
years. And, believe me, Sussex clay is real clay. I have about 10
inches of claggy "soil" over a solid clay subsoil (solid with ironstone
lumps, that is. Even a pickaxe fails to penetrate some parts. and I have
to resort to a hammer drill if I want a deep hole). The most difficult
thing about gardening on clay is digging the damn stuff; it is /very/
hard work. It even sticks to stainless steel spades with a vengeance.
And when dry, don't even bother with a hammer drill - it's not worth the
effort. Wait until it's workable again.
But when it grows stuff, it is brilliant. It holds moisture; it holds
nutrients; it anchors. It tends to help withstand frosts much better
than lighter soils.
I, too, have been growing on clay for about 40 years now... first the clay
subsoil that was all the builders left when they stripped the top soil
and sold it at my childhood home in Iowa, and now out here in Oregon --
both yellow clays, though the Oregon clay is calcium poor, rocky and
nearly free of worms (there are no native worms out here), so it
compacts easily and often requires mechanical aeration-- the Iowa soil
did not require much mechanical aeration and was calcium rich.
I still say it's a difficult soil to learn to grow on. It's hard to
work, and as one who was late to learn about shovel polishing of holes,
it can be unsuccessful just due to hole-digging technique. In fact,
the experience of trying to garden in my childhood home had really pushed
me away from the idea of ever trying to garden. It wasn't until I moved
to an area with a lovely, deep prairie topsoil that gardening became fun.
There, I could stand barefoot on bare soil and wiggle my feet a bit and
dig myself in ankle deep, the soil was that friable and loose. Stick a plant
in the ground and it grew.
But clay presents difficulties to most gardeners that a more balanced soil
does not... especially in the absence of good soil aeration. It can be
particularly tricky because of its cationic exchange properties... it
serves as an excellent buffer until it buffers no more.
Though clay holds soil moisture well, it's often not as available to the
plants as water in sandy soils, e.g.: http://ag.arizona.edu/turf/tips1095.html
which is a special problem in drought. And in comparing plant hardiness
in the soils in Iowa (USDA zone 5), I saw no real difference in frost
protection in clay vs. an organic loam: slope had a much larger effect.
David is, I believe, gardening on arid land clay in S. California;
a friend put her lawn in the front of the house in with (literally) pick and
shovel. When I lived there, my veggies were grown in raised beds to avoid
the salinized clay my house was built on (a failed orange grove).
Is that normal? I don't know anything about Oregon Clay, but would have
though that if there are almost no worms, more-or-less nothing could
grow as recycling of plant material couldn't take place, and aeration
would be non-existent. What happens with the native plants out there?
Or is the area basically a clay desert?
But that's too easy. Don't you want a challenge? ;-)
Here, 70 miles north of San Francisco, we have heavy clay. We scratched
at it for years before getting serious. The final solution was tilling
in sand (probably < %5), and organic material. On this was planted rye
grass, and buckwheat, which break-up, and fills the soil with an amazing
amount of roots. Lastly, we keep the beds mulched, which allow the worms
to do most of the heavy work of turning, aerating (good soil is 50% air
spaces), and draining the soil.
For sure, plants like sequoias, oak, bay, and manzanita can punch
through the clay, but east of here in the town of Sonoma, there is
impenetrable hardpan (clay) a few feet below the top soil, which can
prevent perennials from finding the water they need.
Gotta work with wha'cha got.
Welcome to the New America.
My situation is similar to yours, a layer of topsoil over plastic clay,
though I suspect my topsoil is naturally better. I agree that clay soil
holds water and nutrients well and can produce great crops. Every time the
region goes into drought I thank my stars for the clay underneath that acts
like a big sponge and keeps my pasture growing for months without rain.
Having had very sandy soil (that I was always trying to build up) and very
clayey soil that I have to break down I will take the clay.
BUT You have to have (or to make) actual soil. Clay by itself ( I mean the
plastic stuff you can mould into complex shapes) is hopeless. The process
of amending it takes years of effort and some skill. The choice of plants
has to be considered carefully as many will die in a wet spell due to lack
of drainage and it is impractical (for me anyway) to landscape the whole
garden for drainage and to amend all its soil to prevent the problem. As it
is all my fruit trees grow in mounds and my vege garden has raised beds with
drain paths running down-slope: at considerable effort and cost.
Clay is not for people who just want to plop something in the ground and see
it grow. I thought it interesting that in response to "Treat clay soils
with respect... they're difficult to grow on." you first deny that it is so
and then go on to explain all the difficulties that have. :-)
if you have a properly planted pasture with some
alfalfas and red clovers the tap roots from those
go down quite deep. even for more sandier soils
they can make the difference between a nice top
and barren brown scraggly yuck.
then again, also important is to not overgraze.
lasagna gardening isn't too bad, pile it on and
let time/worms/critters do most of the work. i
just wish i had enough space to do here that wasn't
surrounded by gravel pathways and prone to flooding
once in a while.
without the raised beds here many of the gardens out
back would be too soggy for too much of the spring to
get the soil warm enough. that is one of the problems
with clay that hasn't been mentioned yet (that it stays
cold longer). for some crops this is good, for others
not so good (tomatoes, peppers).
i keep working more organic material in when i
have a chance to do it and the garden is in between
crops/covercropping. still i'm not down very far in
some gardens because we keep rotating the heavier
feeders and i don't have a huge amount of extra
time and energy to dig in more stuff or hunt it down.
so far mixing in partially decayed wood chips along
with some sand if i have it has been the best results
for working, if i could convince myself to get a
breathing rig set up so i could fire more charcoal
in clay lined pits i think that was even a better
result for workability.
i agree with the points about proper drainage
being very important (or a good landscape design)
for clay. until i got the drainage situation
improved here it didn't make much sense to plant
certain gardens early.
for root vegetable beds out back (and the tulips)
i put in raised beds with french drains and drain
tiles to keep the water moving downwards or away
instead of perking the clay back up to the surface.
i put landscape fabric down too before i put the
topsoil/sandy topsoil mix in. i didn't want to
make it easy for the worms to channel into the
clay and mix it with the topsoil either. today
these were the only gardens that didn't get
Did I? Read my post again.
You are confusing "growing" with the act of digging or cultivating. For
the latter, good loam or even sandy soil wins every time, as the job is
easy. But once in, plants grow much better in clay without a lot of
additional help such as watering and use of fertilisers.
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