Mums in the Cold

Douangdara Vang

Abstract

The purpose of this experiment was to test how frost affects perennials, specifically chrysanthemums, hypothesizing that frost will help them grow better. There were two plants, one as a control and one as a manipulated, put into winter-like light conditions. Leaf width and length were measured before and after manipulations for signs of growth. Only the manipulated plant was put into the freezer for frost effects. Soon after the freezing manipulation, the plant died. This refuted the hypothesis.

Keywords: perennials, chrysanthemums, and frost

Introduction

Chrysanthemums (Chrysanthemum morifolium) grow year round because they are perennials. Since Wisconsin weather consists of colder climates during the autumn and winter seasons, newscasters always warn gardeners of expected overnight frosts so they can protect their plants. This year, they specifically stated on Fox6 (WITI, Milwaukee) that perennials will benefit from the frost and grow better. This sparked my interest to test whether frost does help the growth of perennials. It is known that temperature controls a plant's growth process (Jonasson 1999). I expected the plants to grow better after some exposure to frost since their main access to nutrients is in the autumn when microbial population declines (Jonasson 1999) due to the extreme temperature. In addition, perennials have sturdier underground roots (Moffat 1996) for survival year-round.

Methods

The original plan was to use geraniums since their leaves are broader and would be easier to measure leaf growth. Due to the season (mid October), only chrysanthemums were available at the greenhouses. The plants were put in the programmed light chambers in the student research room of the Teaching, Learning, and Technology building at Alverno College (Milwaukee, WI). First, the chambers were programmed to give 16 hr of light and 8 hr of no light in room temperature (around 21 to 24 degrees Celsius) for control settings. After allowing them to get used to these conditions, the light was then programmed to imitate winter light conditions, giving 12 hr of light and 12 hr of no light for the plants. There were two types of mums used: one with daisy-like flowers for the control and another with pom-pom-like flowers for the manipulated. The different flowers will help me differentiate between the conditions I will grow them in.

Eight leaves of each plant were picked pseudo-randomly for measurement of widths and lengths. The measurements were taken in centimeters. The sample was only pseudo-random because the leaves were below and around the flowers, which made it very hard to pick leaves at random. The plants were measured three times: one time during the control setting, one time during the winter-like setting, and one time after the frost manipulation. The plant for manipulation was put in a freezer (about 0 to -1 degrees Celsius) for 3 hr and 30 min to imitate total freezing temperatures overnight during the winter.

Results

Daisies (width, length) control Pom-poms (width, length) control

average

2.0

3.3

1.7

3.1

stand.dev.

1.0

1.5

0.80

0.91

Daisies (width, length) winter light Pom-poms (width, length) winter light

average

1.6

2.9

1.9

3.4

stand.dev.

0.90

1.1

1.1

1.2

 

 

Daisies (width, length) after frost Pom-poms (width, length) after frost

average

1.7

2.8

0

0

stand.dev.

0.65

1.1

0

0

The average, or mean, gives the width and length of the eight leaves combined. The standard deviation shows how different the leaves were from each other for the eight leaves. Overall, all the leaves were very close in size. The greater deviations are expected since there were a variety of young and mature leaves for the sample. The graphs show that the pom-pom flowered mum was growing a little bit better in the winter conditions than the other conditions whereas the daisy flowered mum was slowly declining in growth overall.

Discussion

The experiment refuted my hypothesis because the frost-exposed mum died soon after it was taken out of the freezer. However, I don't think that my method of following growth was very accurate. The graphs show that the leaves of the daisy flowered shrunk and grew again. This is a very false impression because I don't think that a leaf can shrink its cells to a noticeable change in size. In addition, the leaves chosen for measurement weren't marked to have consistent data samples.

Since perennials are known to put so much energy into maintaining their sturdy roots for the winter to survive the following year (Moffat 1996), I think the chrysanthemum exposed to frost was out of energy to recuperate from the extreme temperature. Slowly changing the temperature to become colder and slowly warming the temperature to become warmer after the frost would've been a better way of imitating conditions the plant goes through in a year. The warming would accelerate the litter and the soil organic matter decomposition and nutrient mineralization (Jonasson 1999). This would give the plants a chance to regain what it lost or didn't have during the cold season. According to the experiment Jonasson et.al. conducted, during the arctic season, there was very low or negative net nutrient mineralization measured. This would give a possible explanation as to why the plants died, or slowly died, before the two weeks was over.

Possible changes for follow-up experiments would be to conduct the experiment with geraniums when they are available so there would be better leaves to work with. Also, repot the plants into larger pots to give room for the roots to grow and allow more space for nutrients to rebuild or plant them in a greenhouse. Make the manipulations a gradual change, which means that more time would be needed to complete the experiment, and mark the leaves that are being used to collect data. Another suggestion would be to keep track of microbes in the soil and their effect on the plant's growth during the experiment.

Literature Cited

Jonasson, S, A Michelsen, IK Schmidt, and EV Nielsen. 1999. Responses in microbes and plants to changed temperature, nutrient, and light regimes in the arctic. Ecology 80:1828.

Moffat, AS. 1996. Higher yielding perennials point the way to new crops. Science 274: 1469.