Enough already about reading books about plants. If you're hoping to help plants thrive in a classroom garden, consider the importance of "reading your plants." A leggy bean or yellowed tomato plant might just tell you a thing or two about your gardening practices. What's their story?
Because classroom environmental conditions vary and different factors interact, students may be challenged to figure out just what plants are "saying." By encouraging your class to carefully observe plants and consider their needs (while also sharing some of your horticultural hints), you can help your students become cultivators of thriving gardens -- and better problem solvers to boot.
Before planting or positioning your plants in the GrowLab or other light garden, encourage students to ask questions about the specific care each plant needs. What do we know about this plant? Under what types of conditions does it thrive outdoors? Where did it originate? Tomatoes, for instance, are of tropical origin and thrive with high temperatures and long days, while lettuce is a cool-season crop that requires less light. So students growing a salad garden might choose to grow tomatoes on an upper GrowLab tier and use a humidity tent to trap heat, while placing lettuce and other cool-season crops (such as radishes and peas) on a lower tier, where it's cooler, or at the edge of the indoor garden, where the light is less intense.
Prompt students to notice changes and signs that reveal plant health or indicate how best to nurture plants. Which plants seem to dry out first? Have leaves changed color? Are the younger or older leaves yellow? Are there signs of pests or diseases? Encourage students to use what seem like gardening "failures" as opportunities to examine plant needs and reflect on the classroom growing environment.
By closely observing their green charges and adjusting caretaking practices as necessary, students can begin to explore plant needs and interactions between environmental factors such as light, water, heat, and nutrients. Pinpointing problems can sometimes be challenging. Yellow leaves, for instance, might indicate a variety of problems. Fortunately, plants are resilient and will grow in a wide range of classroom conditions, even if the environment is not "ideal."
National Gardening's GrowLab: A Complete Guide to Gardening in the Classroom provides thorough information on maintaining healthy conditions in classroom gardens. You'll find it a helpful reference whether your class is growing plants on a windowsill, in a homemade light garden, or in a GrowLab.
Turn Challenges Into Opportunities
Trying to "read" plants and help them thrive can present opportunities for problem solving. For instance, if you have a mix of plant heights in your GrowLab, ask students to brainstorm how to ensure that the lights are kept within 2 to 4 inches of the top of each plant. They might prop up shorter plants on overturned pots, slant the lights (no more than 5 inches from end to end), or use one tier for shorter plants and the other tier for taller plants.
Have students consider other ways to increase the amount of light plants receive (by surrounding the garden with reflective material, for instance). Or, if you're growing plants on a windowsill with limited light, research to find out which types of plants are best suited to these conditions. (Plants grown for their foliage, like herbs and lettuce, can generally get by with less intensity and duration of light.)
Classroom plants tend to struggle from either overwatering (being drowned by love) or underwatering. (Undersized pots, low humidity during the winter, and simple neglect are key culprits.) Share with students that it's best to water plants when they need it (e.g. when the soil feels dry an inch down) rather than on a set schedule. To help students consider water needs, ask them to notice which plants seem to dry out faster and to try to infer what might be the cause (e.g., leaf size or texture, plant size, container type). Students might test some of their ideas by setting up investigations or systematic observations.
If plants are dried out on Monday mornings, have students consider how they could maintain water and humidity over weekends, vacations, or other dry periods. (e.g., cover the indoor garden or plant pots with a plastic tent and keep the base material moist).
Classroom gardeners have reported mixed luck with this crop. Here are a few tips for raising ravishing radishes.