Your students have spent all winter and early spring nurturing their classroom plants. As spring emerges, you may be planning to move your precious seedlings into school or home gardens, school or community flower beds, or other outdoor locations. Consider using transplanting as an opportunity to continue teaching about plants' needs and adaptations, and to tie in subjects across the curriculum.
Planning a Calendar. Your students' first challenge will be to decide when to put different plants outdoors. "Cool weather crops" like broccoli, cauliflower, and cabbage can be set out up to a month before the last danger of frost in your area. "Warm weather crops" like tomatoes, peppers, and melons should be transplanted after all danger of frost is past in your area. Annual flowers and other crops vary-students can check seed packets or gardening catalogs for this information. Some suggestions for student activities follow.
* Find out the average last frost date in your area from local gardeners, the Cooperative Extension service, weather maps, or local weather service.
* Count back to determine, based on seed packet information, when to set each plant out. Then develop a planting calendar.
* Find last frost dates for cities in different parts of the country. Discuss why these dates vary.
* Research and make inferences about how plants' cold tolerance or heat preference relates to where in the world the plant originated.
Hardening off. Consider how a living thing might respond if moved from a worm, windless, relatively protected classroom to a harsher outdoor environment. To lessen this shock, we suggest "hardening off" seedlings before planting outdoors. A week or so before transplanting seedlings, set them outside for a short period (1 or 2 hours) during the daytime. Do this for longer periods each day. A couple of days before transplanting, leave them out all night as well. This "hardening off" period, during which leaves actually thicken up, will give many types of plants a better chance of surviving the shock of transplanting. Some activities to enrich this process follow.
* Have students imagine and write from a plant's perspective about being moved from a cozy classroom garden to the outdoors. What new challenges might it face?
* Consider conducting an experiment to discover how the health and growth of a "hardened off" plant compares to one directly planted outside and one left indoors.
Transplanting. Before transplanting, consider the following activities:
* Conduct part 2 of "Why Root for Roots" in GrowLab: Activities for Growing Minds so students can observe how a plant responds when its root hairs are disturbed and broken.
* Conduct "When a Sy-stem" in the GrowLab guide and discuss what role stems play. Then ask students what they can infer about how to treat seedlings when transplanting them.
* The best time to transplant seedlings outdoors is on a cloudy or even drizzly day. This slows water loss as leaves continue to transpire (give off water) while the damaged roots cannot take in adequate water. For each transplant, dig a hole a bit larger than the rootball. Mix in compost or rotted manure if available.
Have students carefully remove plants from containers, keeping as much soil around the roots as possible. Remind students to hold seedlings by their seed leaves and not to tug on or bend the stems. Place the plant in the hole and fill it with soil, holding the plant so it's about the same depth as in the container. Water seedlings well after transplanting. Often after transplanting, seedlings look droopy or wilted since damaged roots have limited ability to take in water. In a few days, you should notice them perking up.
* Use math skills to measure the distance between seedlings (based on seed packet or catalogs), and the arrangement of seedlings in a bed. Consider using a body part such as a hand span to measure distances.
* Water some seedlings before transplanting, and leave others dry. Have students observe and compare the amount of soil that sticks to the roots. What do the observations indicate about the role of roots, water, and soil?
* After transplanting, water some seedlings with a dilute manure tea, seaweed, or other fertilizer. Compare their growth to others given only water. Note: If too strong a solution of fertilizer is used at this stage, it could hurt tender roots.
* Students may want to plant some out on a sunny day, and others on a cloudy day, to compare how plants adjust to transplanting. Based on students' understanding of plant structures and needs, discuss why plants may respond better on a cloudy day.
* Sturdy, healthy plants are best able to survive the shock of transplanting. Challenge students to describe any analogies this has for humans.
Although most plants like to be transplanted to the same depth as in their original container, tomatoes are an exception: They actually prefer being planted more deeply. When parts of their stems are buried in soil, small adventitious roots will form underground on the stems. Students might want to investigatethis by planting some tomato plants deeply, and others at the same level as they were in the pot. Discuss how this adaptation might help plants survive in different environmental conditions.