Horticultural Intergenerational Therapy (HILT) is a successful program that uses horticulture to benefit the elderly by increasing their physical activity and mental stimulation.   It also benefits youth by introducing them to concepts of horticulture as well as showing them how to cultivate relationships with the elderly.   Tells how to plan a HILT program, organize participants, and obtain funding.   Includes long-term activities, such as planning an outdoor garden, planting bulbs and seeds, drying flowers, and building birdhouses.   Provides lists of materials needed to accomplish each project, 30 ways to hold gardeners' interest, and factors influencing germination.