I have a lawn with clay underneath that floods every time it rains; it's
also full of tree roots.
I have killed the lawn off, built "edges" and a deck/pier to walk
around on. I plan to top-dress the old (now dead) lawn with homemade
compost and well-rotted horse manure to a depth of about 6 inches,
thereby introducing organic matter, and avoiding having to dig too
much. I have "loosened" the soil where possible.
Any thoughts? Anything wrong with this approach? I will not start
planting until next year (herbaceous shrubs, roses and annual
Is this a sensible strategy? Have I missed anything?
Thanks - Bruce
The clay barrier will still be there. The organic material will
decompose and disappear, and you'll be back to where you started.
Now if you could incorporate this organic material, and a few inches of
sand into the top 6" to 12" of soil (perhaps you could hire someone to
do it, or do it yourself in stages), you would provide soil microbes
with an environment where they could create even more (deeper) soil.
You would need to use organic fertilizers, like fish emulsion, to
occassionally give the soil community a boost in nitrogen. The ecology
of your soil will provide nitrogen from the life cycles of its microbes
(bacteria, fungi, nematodes, and worms (not to mention a large number of
arthropods). This nitrogen is locked into the soil. This community of
soil flora and fauna will encroach on the clay beneath it, creating even
Chemical fertilizers kill large portions of this interdependent, soil
community. Moreover, chemical fertilizers are water soluble and are
easily flushed out of the soil with water to pollute waterways and local
drinking water sources. All studies on the effects of chemical
fertilizers on top soil, show loss of top soil.
I believe the above is a viable long term solution.
Racial injustice, war, urban blight, and environmental rape have a common
If you create an area with strata of unlike soils, you will find that
plants will not thrive. Roots of your shrubs and vegetables will not
readily grow through the interface between strata. Water will not
penetrate through the clay, and you will still have some flooding.
I suggest that you broadcast gypsum over the area, creating a 1/4 inch
coating over the soil. Lightly water the gypsum to start it dissolving;
then water it into the soil 2-3 times. This will help break up the clay.
Then rent a power tiller. When the clay is slightly moist (definitely
not wet), till the area to a depth of two feet. Top dress with about 3
inches of your homemade compost and well-rotted horse manure. Till
again to a depth of a foot. Then top dress again with another 3 inches
of the compost and manure. Till one more time to a depth of only 6-9
If you don't walk on the area when it is truly wet, you won't have to
work the area for several years. You will also find that plant roots
will eventually grow well below the depth that was worked. However, you
might have to spread more gypsum annually to replace what has leached
away; this will keep the clay porous and well-draining.
David E. Ross
Climate: California Mediterranean
That would work even better if the cover crop were planted after the
initial gypsum treatment and the first tilling. The roots of the cover
crop would then more likely penetrate the clay. Afterwards, a second
gypsum treatment would be appropriate.
David E. Ross
Climate: California Mediterranean
If water puddles on your clayey lawn area now simply adding a top dressing
won't help, whenever it rains you'd just have more volume of soupy mud...
you need to get down below the clay so it can perc or devise some way to
drain the water away. My first cause of action would be to attempt a deep
rototilling in hopes of getting below the clay. Next attempt would be to
create drainage away from that area, perhaps with a series of trenches that
hold perforated pvc pipe and covered with gravel... essentially creating a
leaching field. Then add a good thick layer of rich soil. But odds are
that clay runs deep rather than shallow. To me it seems like you may want
to do something different with that area rather than planting a lawn,
perhaps an attractive flagstone patio built on a porous base. Good luck.
An area that floods over a clay base is not going to be productive for roses
or veges so you need to address the drainage issue. You could:
- divert ground water away from the area and/or
- build raised beds and/or
- add drainage lines in filled trenches.
Prolly best to ask this question in uk.rec.gardening so I am replying to
your post and adding a crosspost to that group too.
The has been a problem in the UK with horse manure being contaminated with a
strong residual herbicide. You'll need to know about this so you can source
good quality horse poo and the UK newsgroups has a lot of keen gardeners who
give good advice.
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