Irrigating Potted Plants with Milk and Vinegar
Plants require at least 14 essential elements, or
essential mineral nutrients, that they usually absorb
via their roots from the soil solution. The six
macronutrients, needed in fairly large amounts, are
nitrogen, phosphorus, potassium, calcium, magnesium
and sulfur. The eight micronutrients, needed in much
smaller amounts, are iron, boron, manganese, zinc,
copper, molybdenum, chlorine and nickel. No natural
deficiencies of chlorine and nickel have been seen
because those two elements are relatively abundant in
soils relative to plant needs. Potted plants are often
irrigated with a fertilizer solution. Plant scientists
often grow plants without soil in a Hoagland solution,
or other mineral nutrient solution, to assure their
plants have all the essential mineral nutrients. Here
is an excellent website on plant mineral nutrition:
http://www.soils.wisc.edu/~barak/soilscience326/essentl.htm
The following USDA website indicates that cider
vinegar contains some essential mineral nutrients,
including significant amounts of potassium (730
mg/liter), phosphorus (80 mg/liter), calcium (70
mg/liter) and magnesium (50 mg/liter). Compare these
numbers to those for a Hoagland Solution at the
bottom. Note that the USDA tables use units of mg per
100 grams. Multiply by 10 to get standard units of
mg/liter.
http://www.nal.usda.gov/fnic/foodcomp/search/
The main ingredient in vinegar is acetic acid, which
has an acid pH and would make water less available to
the plant roots. Aloe vera is a succulent. Succulents
can withstand low soil water availability better than
most nonsucculents. Thus, perhaps it can tolerate the
acetic acid better than many plants. Soil pH has a
major effect on the availability of several mineral
nutrients to plant roots. Thus, vinegar changing the
soil pH might affect the amount of mineral nutrients
available to the roots. See the soil pH nutrient
availability graph in the following webpage:
http://www.extension.umn.edu/distribution/horticulture/components/1731-03.html
Milk has too high a salt (sodium chloride)
concentation for irrigation of most plants. The higher
the concentration of salts and other dissolved
substances in the soil solution, the more difficult it
is for plant roots to absorb water. In addition, the
proteins, sugars and fats in milk provide an energy
source for microbe growth. Microbes can produce waste
products that harm plant roots or compete with plant
roots for mineral nutrients. Check the soil of the
milk-irrigated plant for bad odors, a sign of toxic
microbial waste products.
Based on the label, Hershey (2001) calculated that
skim milk contained 520 mg/liter sodium, a very high
level for plant irrigation water. If you can get an
electrical conductivity (EC) meter, you can easily
compare the EC of your three solutions to get an idea
of how good they are for plant irrigation (Hershey and
Sand 1993). The higher the EC, the worse the water is
for plant irrigation (Hershey 1993). Hershey and Sand
(1993) reported that 1% milk had an EC of 5.2 dS/m.
Excellent irrigation water has an EC below 0.25 dS/m.
Milk does contain very high concentrations of many of
the essential nutrients for plants, especially
calcium, magnesium, phosphorus, zinc and potassium.
Check the USDA website mentioned earlier and compare
the levels in milk to the Hoagland solution.
Important questions in this experiment are the
following:
1. The chemical and physical properties of the soil.
Was it field soil or potting soil? Did it contain any
starter fertilizer? Field soils in pots often give
very poor plant growth because of their poor physical
properties (Hershey 1990a).
2. The chemical composition of the tap water used as
the control. Did the tap water provide significant
amounts of any essential mineral nutrients, such as
calcium, potassium and magnesium? Your water company
can provide a chemical analysis of the tap water.
3. Was any fertilizer added? If so, what type and
amount?
4. What effect did the vinegar have on the soil pH
compared to the control?
5. Which is cheaper per liter, a fertilizer solution
designed for irrigating potted plants, such as
Miracle-Gro, or milk or vinegar (Hershey 1990b)?
Irrigating plants with human beverages, such as soda,
milk, tea, coffee, fruit juice, etc., is a common
student project but contradicts basic biological facts
that photosynthetic plants get their energy mainly
from light and require only mineral nutrients and
water from the soil. A better way to present such
projects would be to consider what the effect on
plants would be if tanker truck of milk or vinegar
spilled or whether outdated milk or vinegar could be
safely disposed of or recycled by using it to irrigate
plants.
References
Hershey, D.R. 2001. Re: Why did the liquids kill the
plants? Why did the tea do well?
http://madsci.org/posts/archives/2001-02/981520898.Bt.r.html
Hershey, D.R. 1993. Evaluation of irrigation water
quality. American Biology Teacher 55:228-232.
Hershey, D.R. and Sand, S. 1993. Electrical
conductivity. Science Activities. 30(1):32-35.
Hershey, D.R. 1990a. Container-soil physics and plant
growth. BioScience 40:685-686.
Hershey, D.R. 1990b. Sleuthing the nutrients that make
your houseplant grow. Science Activities 27(4):17-20.
http://www.angelfire.com/ab6/hershey/safertilizer.pdf
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For comparison, a Hoagland Solution number 1 contains
the following in mg/liter:
Nitrogen 210
Phosphorus 31
Potassium 234
Magnesium 48
Calcium 200
Sulfur 64
Iron ~1 to 5
Boron 0.5
Manganese 0.5
Zinc 0.05
Copper 0.02
Molybdenum 0.01
David R. Hershey
http://www.angelfire.com/ab6/hershey/bio.htm
In reply to:
I am in middle school. I am also doing a science
project on how different liquids affect plant growth.
The plant I am using is "Aloe Vera"
I need the know the certien nutrients needed for this
plant to grow. I've been searching on the internet for
days but haven't found what I needed. The liquids I am
using for my project are milk, vinegar, and plain
water for my control. The nutrients so far have been
helping the Aloe vera plant grow with vinegar. The
milk plant's soil is extremely rough and the water on
is growing slowly. The vinegar plant is growing very
quickly. If there's any help you can give me please
help.
Jesus
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