As dynamic ecosystems, gardens offer boundless opportunities for curious young observers to ask questions and pursue fruitful investigations in their living garden laboratories. If we jump at short-term solutions to "problems" that arise, children can lose the opportunity to develop a deeper understanding of the complex interactions among plants, insects, weather, soil conditions, and human horticultural practices. By understanding what makes our gardens and plants attractive to insects and diseases, and how to maintain plant and soil vitality, youngsters learn important lessons about how to work with nature to create a resilient system.

Promoting Plant Health. Your garden ecosystem may be home to plant pests—slugs, insects, nematodes, fungi, bacteria, and viruses—but their presence doesn't necessarily count as a threat to plants. Like healthy people, healthy plants are usually able to ward off or weather a time of stress or illness and continue to perform well. To promote plant health and vigor, follow the soil-building and garden maintenance practices we've discussed above. The list below suggests ways to minimize pest and disease buildup in the garden. These are the basic steps to follow to maintain a healthy garden.

• Practice crop rotation. Pests and diseases that affect certain crops (or families of crops) build up in the soil if the same crop is grown in a bed year after year. By planting a different crop in the bed each year on a three-year cycle, you can avoid many problems.
  
Discourage excess moisture on foliage. Most fungal and bacterial diseases can infect plant surfaces only if there is moisture present. In regions where the growing season is humid, provide adequate space among plants so that air can circulate freely. Try to stay out of the garden when it's wet so you don't spread disease organisms.

Plant disease- and pest-resistant varieties. Some varieties of crops are naturally less susceptible to problems, and plant breeders have developed many others. Look for resistance information in variety descriptions in catalogs and on seed packets.


Clean up your garden. Diseases and pests can remain on infected and dead plant material, making it easy for them to attack other plants. Remove infected plant leaves, keep weeds to a minimum, and clean up the garden at the end of the growing season.


Encourage beneficial organisms. Make your garden inviting to pest predators such as ladybugs, wasps, and birds. Flowers and herbs provide nectar to predatory insects, and a water source, such as a fountain or bath, will attract birds.

• Handpicking. Have students inspect plants and soil for pests in all life stages (egg, larva, pupa, adult). Pick and crush pests, or collect them in a can of soapy water.


• Barriers. Floating row covers are made of lightweight fabric that you can place over plants to protect them from invading pests. The fabric allows light, moisture, and air to pass through. If you cover a crop that requires insect pollination in order to bear fruit, you will have to remove the covers when the plants begin to blossom. Row covers may also deter some animal pests, but fences are often the only way to keep large, persistent creatures out of the garden. Use netting to protect fruit crops from hungry birds. A collar of newspaper, stiff paper, or boxboard circling seedling stalks and extending 2 inches above and below ground pre vents cutworm damage.


• Biological control. This term encompasses living organisms that are pests' natural predators, parasites, or diseases. For instance, ladybugs and lacewings are natural predators of aphids. Different strains of the bacteria Bt (Bacillus thuringiensis} infect cabbageworms and potato beetles. Most bio-control methods do not harm creatures other than pests, but some aren't so exclusive. For instance, the Bt strain that kills cabbageworms can also infect the larvae of all other moths and caterpillars. To reduce the risk to non-pest organisms, follow the application directions exactly. You can encourage some beneficial creatures to visit your garden, or you can purchase them through catalogs.

• Insecticidal soaps. These kill or repel a wide variety of insects, including aphids, leafhoppers, and spider mites, by dissolving their protective outer shell.


• Sprays from the pantry. Gardeners have long used homemade concoctions of items from the pantry, including baking soda, garlic, and cayenne pepper. Now there are commercial formulations based on these substances. Potassium bicarbonate spray (similar to baking soda spray, which was tested first) prevents several fungal diseases, including powdery mildew. Garlic and pepper sprays are recommended as repellents for soft-bodied insects such as aphids, spider mites, and whiteflies.


• Horticultural oils. These refined petroleum- or vegetable-oil based formulations can be sprayed any time of year on most plants to cover and kill pest eggs and clinging insects such as scale.