[Fwd: Re: [Fwd: Re: raised beds on wet soil]]
- Subject: [Fwd: Re: [Fwd: Re: [cg] raised beds on wet soil]]
- From: Don Lambert <firstname.lastname@example.org>
- Date: Sun, 17 Mar 2002 17:56:44 -0600
-------- Original Message --------
Subject: Re: [Fwd: Re: [cg] raised beds on wet soil]
Date: Sun, 17 Mar 2002 17:48:48 -0600
From: Don Lambert <email@example.com>
To: "McKenna, Valarie" <firstname.lastname@example.org>
Gravel has several drawbacks. It is full of spaces, which could allow
water to drain away, but may also create a aquarium effect, some one
used the term "perched water table," a layer where there is space for
water to hang out. If there area is already too wet, gravel will not
force water to move on like soil would.
Secondly, my understanding of the fabric is to keep your good soil from
settling and washing down into the gravel layer. Fine soil particles
will go through, and if the fabric is so tightly woven as to prevent
this , then it will be plugged up by the fine soil, organic matter, and
roots, so that water, air, earthworms, etc. will not be able to pass the
fabric layer. Either roots will find it hard to penetrate the fabric,
and you will get a root layer like forms in the bottom of a potted
plant, or they will go through and fairly quickly tear up and get
tangled in the fabric.
In my experience (inheriting a garden done wrong by previous folks) you
get a compacted zone of roots and particles just above the fabric that
within a year or two that will contribute to plant growth problems,
diseases, and percolation problems, that will be impossible to fix
without starting all over.
I had to rebuild a large community garden that used fabric to keep soil
from escaping out the bottoms on boxed raise beds. After several years
plants were unhealthy because even though the ground was wet, roots
could not get through the fabric to the wet soil below. Even though
gardeners watered frequently, the water went through the fabric and the
roots could not get to it. After very heavy rains, water stood in some
beds, where the clogged fabric would not let the water pass through.
Renovation was hell because digging out fabric and tangled roots has a
foot by foot hand job, as fabric and tillers to not get along well
together. The soil layer just under the fabric was very hard and
compacted, pretty much dead and devoid of life, probably the fabric-root
layer just sealed it off so little could live there. If there had been
a gravel layer below the fabric, the water problem would not have been
helped, and we would probably have abandoned the site because it would
have been too costly to have that layer dug out, hauled away, and new
soil brought in.
It sounds to me like you may be heading for the same mistakes if you use
fabric and gravel under garden beds. I know that landscapers use some
techniques that include such things, but I have seen them back re-doing
these beds every few years, usually by removing stuff and replacing with
new layers topped off with soil-compost mixes.
McKenna, Valarie wrote:
> Can you be more specific about the problems you foresee with fabric or
> gravel. I'm in a position where I will need to justify my
> Thanks. Valarie
> -----Original Message-----
> From: Don Lambert [mailto:email@example.com]
> Sent: Friday, March 15, 2002 9:33 PM
> To: CG
> Subject: [Fwd: Re: [cg] raised beds on wet soil]
> -------- Original Message --------
> Subject: Re: [cg] raised beds on wet soil
> Date: Fri, 15 Mar 2002 23:25:28 -0600
> From: Don Lambert <firstname.lastname@example.org>
> To: "McKenna, Valarie" <email@example.com>
> You simply need bed height that keeps you far enough above the wet soil
> so that healthy roots can grow. Having water flood over beds during
> heavy rainfall is okay if the water can drain away within a short period
> of say half a day, and the bed surface is at last 6 - 8" above the water
> You need to have plants well established before heavy rain periods,
> because seedlings have little tolerance to wet conditions. We
> frequently have flooded gardens, and virtually always can find water a
> few inches down. While not the best, many plants will tolerate this,
> for example, virtually all Asian origin crops were adapted to thrive in
> very wet soils and just a few inches of soil above saturated sub-soil
> Do NOT add a gravel layer or fabric, as this will cause problems. Put
> the same money into more bed height, bring in a few more inches of soil
> to fill your beds. Look for ways to add drainage. In part of our
> garden we just built higher beds, and mulched all non-beds with deep
> layers of woodchips which over several years increased the capacity for
> excess water to move through the soil.
> This is about a far as I can go without seeing your site and knowing
> more about your type of soil, elevations and terrain, setting around the
> garden, bed edging materials, etc.
> Don Lambert
> Gardeners in Community Development
> McKenna, Valarie wrote:
> > I have started working with a teachers at a local middle school
> > laying plans for a raised bed garden. The ground on which the
> > be placed is typically soggy during the rainy season and there's some
> > concern that the soil in the beds will not drain properly.
> > suggested that a layer of fabric and then a layer of gravel be
> > the bottom of the beds before the soil.
> > My concern is that roots would be too restricted in a 8 to 10 inch
> > of soil as the roots will be unable to reach threw to the ground.
> > I would be concerned that worms and other beneficial critters
> > be able to reach the soil in the beds with this barrier.
> > Any comments or suggestions on this?
> > Thanks. Valarie
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