8
in other words
november 21
2019
Diggin’ in The Dirt: Planting Over Septic Fields
By Chip Bubl
Oregon State Extension Service
Columbia County
Master Gardener™ class sign-ups
being taken for 2020 class in St. Helens
The OSU Extension office in
Columbia County will be offering the
Master Gardener™ training again this
spring. This year, we are trying a new
schedule that allows people that work
to attend. The classes will be held on
Wednesdays from 6 - 9 pm and on al-
ternate Saturdays from 9 am - 4 pm for
about 10 weeks starting on February 5,
2020 at the Extension office in St. Hel-
ens. Cost of the program is $100 which
includes a large resource book. Some
scholarships are available. Master Gar-
deners are responsible for providing vol-
unteer gardening education to the com-
munity as partial payback for the train-
ing. If interested in the program, call the
Extension office at (503) 397-3462 for
an information packet. Online registra-
tion is now available at https://tinyurl.
com/ColumbiaMG2020. We can also
send you an application and/or you can
come into our office to sign up.
Planting over septic fields
A recent review of articles about
planting on a septic drain field offer a
range of opinions about what, if any-
thing, is suitable. The concerns seem
to be focused on three areas: that com-
paction of the soil over the drain fields
by gardening activities may lead to a
reduced life for the field; that root en-
croachment into drain lines can lead to
their failure; and the risk that septic ef-
fluent might contaminate fruits or veg-
etables grown over a septic field with
human pathogens.
A septic drain line is
engineered to function with
the natural soil drainage and
rainfall to decontaminate the
effluent. Adequate aeration is
crucial to make the system work. Often,
lines are covered with gravel/sand at in-
stallation to improve aeration. There is
a concern that adding soil (as in raised
beds) over the septic lines can upset the
oxygen flow into the drain lines. I am
not sure how valid that is. However, ro-
totilling, livestock grazing, and/or walk-
ing or routinely driving anything over
the drain field area when the soil is wet
will compact it. That will restrict oxy-
gen penetration and lead to a degraded
system. While the impact of those activi-
ties may not be immediately seen, there
is good evidence that it may shorten the
life of the field from 40+ years to some-
thing less. However, data is sparse on
this topic
Other writers take the position
that it is possible to grow something be-
sides grass as long as the beds are not
compacted by the activity. The most
common materials recommended are
herbaceous perennial flowers, ornamen-
tal grasses, ground covers, and shallow
rooted shrubs like lavender, azaleas,
rhododendrons, and blueberries. Annual
mulching to keep the soil surface loose
and the weeds down should keep the
aeration in good condition.
One writer suggested making
the surface of the actual drain lines into
paths covered with gravel mulch and
growing plants in the space in between.
I’m not sure that is a good idea.
There is general agreement that
deep-rooted trees should be avoided.
There is plenty of evidence that some
tree roots will invade drain lines and
can plug them up. Cotton-
woods and willows have
a fairly bad reputa-
tion in this regard,
but I can’t imag-
ine many trees
passing on the
opportunity
for the nutrient
filled drink that
the drains lines
provide. Since
effective.
There also is agreement that if
you decide to grow vegetables over the
drain line, plant only those whose ed-
ible portion is held up off of the ground.
There is no evidence of disease trans-
mission from septic effluent through
roots and systemically into a plant. The
concern is that human pathogens in sep-
tic effluent might attach to the surface of
the edible portion of a plant, especially
if that edible portion is in the soil like
an onion, carrot, or beet. Leafy greens
are at risk from rain splash of septic con-
taminated surface water. Safe choices
include corn, and trellised crops like to-
matoes, beans, peas and cucumbers.
If your system is failing (a good
sign is a rotten egg smell) it is important
to get a new drain line put in as soon as
possible.
Lime for lawns and gardens
Limestone is a mineral widely
used in farming. Limestone, which is ei-
ther straight calcium carbonate or a mix
of calcium and magnesium carbonate
(dolomite), is mined and then ground to
a fine consistency. Lime works wonders
when tilled into soils. First, it provides
calcium and magnesium which are de-
ficient in Columbia County
soils. Second, as lime
reacts with the soil
chemistry, it makes
the soil less acid.
We say it rais-
es the pH of
the soil. Most
plants prefer a
near neutral pH
of 6.5-7. Our
soils often test at
fruit soils. Most berries like lime, though
at a slightly lower rate except blueber-
ries which prefer very acid conditions
and should not be limed. Lawns should
have about 100 pounds per 1,000 square
feet applied as a more finely ground
“prilled” product (one trade name is Cal-
pril). Flower and shrub beds will do fine
with about 75 pounds per 1,000 square
feet but again, don’t fertilize acid loving
shrubs like rhododendrons and azaleas.
Free newsletter (what a deal!) The Or-
egon State University Extension office
in Columbia County publishes a month-
ly newsletter on gardening and farming
topics (called Country Living) written/
edited by yours truly. All you need to
do is ask for it and it will be mailed or
emailed to you. Call (503) 397-3462 to
be put on the list. Alternatively, you can
find it on the web at http://extension.
oregonstate.edu/columbia/ and click on
newsletters.
Take excess produce to the food bank,
senior centers, or community meals
programs. Cash donations to buy food
are also greatly appreciated.
The Extension Service offers
its programs and materials equally to
all people.
Contact information for the
Extension office
Oregon State University
Extension Service – Columbia
many of our trees have roots that extend
as much as 30% beyond the width of the
mature crown, careful location of land-
scape trees is very important. There are
root barrier fabrics that can be installed
to keep tree roots from the lines but of-
ten those are best put in when the drain
field is installed. They also aren’t 100%
a pH of 5.5-6. As the soil becomes less
acid, the plant is better able to extract
important plant nutrients like phospho-
rus and potassium.
Most vegetable garden soils can
benefit from about 125 pounds of lime
per 1,000 square feet of garden once ev-
ery three years. The same goes for tree
Where Do You Read The Voice?
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by email to: Scott@VernoniasVoice.com.
County
505 N. Columbia River Highway
(across from the Legacy clinic)
St. Helens, OR 97051
(503) 397-3462
Email: chip.bubl@oregonstate.edu
Vernonia’s Voice is published
twice each month on the 1 st
and 3 rd Thursday. Look for our
next issue on December 5.
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