Pollinator Presumptions
Challenge students to guess how each type of plant might be pollinated, based on the characteristics of its emerging flowers. (Those pollinated by insects and other animals tend to have bright, showy flowers. Wind-pollinated flowers tend to have less conspicuous ones.) When the trees flower in the spring, students can observe how pollen is moved from flower to flower on different types of trees.

Pondering Pruning
Gardeners also cut branches, twigs, and stems (pruning) from trees and other plants to improve their health, shape, and/or yield. This practice can open up more leaves to sunshine, increase air flow to prevent disease, and/or divert sugars to fruits rather than new vegetative growth. Invite students to explore how plants respond to pruning by experimenting with tomato plants, which grow relatively quickly.

Explain to your class that some gardeners routinely nip off parts of tomato stems in a practice called pruning. Ask students to consider why this might be done and how tomato plants grown this way might compare with those allowed to grow freely. Encourage them to explain their responses and set up an investigation to test their hypotheses. Consider the following approach.

Choose an indeterminate tomato variety. (These continue to grow and fruit as long as environmental conditions are favorable. Determinate tomato varieties cease to grow and blossom after setting their main crop of fruit.) Plant at least four seedlings (two experimental and two control) in containers or garden beds. Once suckers start to appear — new branches that form in the junction between the main stalk and leaf stems — pinch them off, keeping just one or two main stems. Students might decide to support the plants with stakes or cages as they grow, or allow them to sprawl. (In either case, they should treat the control plants the same way.)

When plants are still young, ask students what they think they should observe or measure, such as growth rate, total yield of fruit, average size of fruit, or other indicators of plant health. (They might even want to compare factors like fruit attractiveness or flavor!) Have them set up a schedule for pruning and gathering data.

Once they've gathered and analyzed data, ask, Why do you think the plants responded the way they did? (Generally, if a plant has fewer stems, it will divert more sugars to the fruits. Although it might produce fewer fruits, they should be larger than those on an unpruned plant.) Ask, If you were commercial tomato growers or market gardeners, which method would you use? Don't look for a "right" answer, but encourage a thoughtful discussion.

Another Option: You can attempt a similar project indoors under grow lights with geraniums; they won't take over the classroom! Regularly pinch back stem tips on several plants, and compare them with unpruned (control) plants. Keep top leaves within a few inches of the lights. Compare growth habit, blossoms, and overall appearance. Ask students which they would buy from a florist or garden center. (If you have the room, you can pot up the prunings to make more plants!)