Radishes, Roots, and 'Rithmetic

By Eve Pranis, June 23, 2008

"My students had always disliked math," reported a fourth grade teacher from Hartford, CT, "but when we started a classroom garden, they eagerly figured out how many hours to leave our lights on, measured and graphed growth rates, and predicted when their vegetables would be mature. Their excitement about growing things helped their math skills soar."

Like language, math is integral to the science process -- opportunities flourish for tying in and reinforcing math concepts with your classroom growing experiences. From basic measurement, sorting, and classification to more elaborate problems, surveys, and record keeping, plants motivate and provide a context for student interest.This article features ideas from growing classrooms on weaving math into classroom gardens.

Solving Problems

* Determine how many seeds per row or container will be needed if a packet says to plant X seeds every X centimeters.

* If you have X plants, what are several ways you can group them when transplanting them outdoors (e.g., 4 rows of 4 each or 2 rows of 8 each)?

* To determine if old seeds are still healthy, try germinating 10 on a moist paper towel placed in a plastic bag. Figure out the percentage germinated, and determine whether they're worth planting in the garden!

* Estimate and verify the number of seeds in a fruit. Predict how many fruits you'd have if they all germinated and each plant produced X more fruits. Discuss what prevents this from happening in nature.

* Given the recommended dose of your fertilizer and your average rate of watering, calculate how much fertilizer you'd need for a week, a month, or a year of indoor gardening.

* Figure out the fraction or percentage of seeds that actually sprout of those planted in a given container.

* Try some root growth rate problems. For instance, roots of young seedlings can grow at .2 mm per hour. At that rate, how long would it take a carrot root to reach the bottom of a 10-cm pot? Discuss and investigate whether plant parts grow at the same rate throughout their lives.

* Dig up a set volume of soil from outdoors. Count the number of earthworms, and estimate the total number of worms in an area.

* Identify plant parts in different foods, using school lunches as a springboard (e.g., bread from seeds, pizza sauce from fruit, etc.). Calculate and graph the percentages of different plant parts represented in a typical school lunch.

* Determine when to start seedlings indoors for spring plantings based on the days to maturity and recommended dates for transplanting out in your area.

* Challenge teams of students to grow the biggest...longest...heaviest of a particular vegetable. Keep daily records, develop criteria for determining winners, graph results, and conclude with a feast!

Identifying Patterns

* Investigate mathematical patterns in nature. For example, is there a relationship between number of flower petals to number of stamens and pistils? Is there a relationship between the size of a fruit and the size or number of seeds?

* Make leaf rubbings with crayons. Identify and classify different leaf vein patterns.


* Have students sort and classify leaves into different types, then calculate the percentage of the collection each category represents.

* Predict, then count, compare, and graph the number of seeds inside different fruits.

* Draw Venn diagrams, showing intersecting sets, to categorize fruits and vegetables. One set should show fruits; the other, vegetables. The intersection should show those fruits we commonly consider vegetables.

* Sort a small amount of birdseed; glue seeds on paper to make a graph showing the numbers of different types of seeds in the mixture.


* Draw a map, to scale, of your GrowLab indoor or outdoor garden.

* Measure and compare areas, lengths, and circumferences of different plant parts under different growing conditions.

* Compare and graph growth rates of a fast-growing plant (e.g., beans) with a slow-growing plant (e.g., carrot).

* With a waterproof marker, draw rings on the stem of a bulb, bean, or other straight plant stem at 1-cm intervals. Measure and graph the distance between the rings daily for one to two weeks to see how stems grow. Consider exploring whether this growth changes as light and temperature change.

* Determine the volume of soil mix necessary for X pots.

* Grow sprouts for a salad. Measure a certain volume, estimate the number of seeds, measure the change in volume that the sprouts occupy daily. Note changes in weight over time.

* Estimate the weight of each ingredient in your classroom salad garden, then weigh and graph the percentage of the total that each ingredient occupies.

* Compare different plant roots by measuring and trying to estimate the total root length.

* Use string to measure the lengths and circumferences of non-straight roots, fruits, leaves and other plant parts.

* Calculate and compare the surface area of different leaves by drawing outlines on graph paper.

Plant-Related Businesses

Earning money with plants has been a math motivator for students in a number of gardening classrooms what have sold everything from house plants and seedlings to sprouts to worm castings (dubbed "zoo-doo"). A range of math skill are required -- from developing a plan, projecting costs and sales, to actually selling, making change, and reporting on profits or losses. Lou Meyers' high school students' plant business actually "incorporated," allowing students to purchase stock for 25 cents a share. Syndee Malek in Michigan reported that her fifth graders had their eyes opened to the harsh realities of business after dreaming about profits from their plant sale. It seems that students had not at first recognized that they would have expenses to deduct from their profits!

Salad Survey

Pat Pierce's Bristol, VT fourth and fifth graders became immersed in math when they decided to conduct a "salad survey," suggested in GrowLab: Activities for Growing Minds, to determine the salad ingredient likes and dislikes of their families and fellow students. Groups first brainstormed a wide range of salad ingredients and the class settled on ten for the survey.

"They really had to think things through at each step," said Pat. "Each group was then challenged to develop a graph to represent their findings. They translated their graphs to computers, calculated the percentage of respondents favoring each vegetable, and described the whole project on wall charts."

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