Azalea Boys
Edward Murray
Justin Turner
Monique Koll
Eric Guitreau
Abstract
Our experiment tested the effect of soil pH on
the growth of transplanted azaleas. Past studies have shown that azaleas
grow optimally at a lower pH than offered in many premixed potting soils.
The height, number of branches, and number of blooms were the criteria
used to determine azalea health. Our hypothesis is the lower the soil pH,
the better the azalea growth. Our hypothesis was rejected since the azaleas
grown at pH 5.5 performed better than those at
pH 4.8. Other results were as expected.
Introduction
Azaleas require acidic soil values for optimum growth. Many prepared soil mixes have higher pH values than the values needed by azalea plants. Our hypothesis is that these acid lovers should thrive better as pH drops. Soil pH is altered and adjusted using aluminum sulfate and lime as necessary. Azalea health is assessed by recording three quantitative values: height, number of branches, and number of blooms. According to the hypothesis, the soils with the highest pH will have the lowest values for the plants in these areas. Eight azaleas divided into four pH groups are analyzed once a week for a six-week period. The pH levels are as follows: the control group averaged a pH of 7.0, the first group a pH of 6.5, the second group a pH of 5.5, and the third group a pH of 4.8.
Materials
(8) 1-gallon pots
(4) 2-gallon pots
(8) 6-inch azaleas
(8) gallons of Olivier Ap soil
(1) 5-lb. bag of aluminum sulfate
(1) 5-lb. bag of lime
(1) bag of 15-5-10 fertilizer
(1) pH meter / electrode
Methods
1. Separate 8 gallons of soil evenly into
4 2-gallon containers.
2. Use pH meter to measure the pH of all
four soil samples.
3. Record values.
4. In the pot labeled "control," add 10
ml of aluminum sulfate. Record pH. Incubate for 5 days.
5. Repeat this process for each set of
soil samples. Record pH after each amendment and
allow to incubate
for 5 days.
6. After incubation, measure and record
pH values of each pot.
7. Repeat steps 4-6 for the pots until
the following values are obtained:
pH 7.0, 6.5, 5.5,
and 4.8.
8. In cases where pH has dropped below
target value, add 10 ml of lime and incubate
for 5 days.
9. Measure and record pH values.
10. Divide soils into 8 1-gallon pots and label
appropriately.
11. Plant one six-inch azalea into each pot.
12. Measure the height, number of branches, and
number of blooms present on each plant
weekly. Record
this data.
13. Repeat step 12 every week until experiment
concludes.
14. Make pH readings every 2 weeks. If deviations
occur from desired values, adjust pH
according to the
procedure outlined in steps 4-7, but only allow incubation for 3 days.
15. Add 15-5-10 fertilizer to each pot every
2 weeks.
Results
This experiment began on Saturday, October 16 and concluded on Saturday, November 27, 1999.
Table 1. pH values.
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Table 2. Height in inches.
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Table 3. Number of branches.
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Table 4. Number of blooms.
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Discussion
In support of our hypothesis, the azalea growth
was best in acidic soil based on our growth
criteria. The plants grown at a pH of 6.5 had
the lowest height, number of branches, and number
of blooms. The pH 5.5 group had the best performance,
second to the lowest pH group at 4.8,
which is not in support of our hypothesis. This
deviation suggests that pH 4.8 is lower than the
optimal growth range for azaleas. It is clear
that a reduction in pH in the experimental groups
was beneficial and even essential for azalea
growth. The addition of soil amendments such as
lime could have negative effects on such pH limited
plants. In soils with high buffer capacities,
the amounts of amendments needed to adjust pH
will vary and may require more frequent pH
measures to attain the optimal pH ranges for
azaleas. We conclude that the optimal growth range
for azaleas is pH 5.5.