Before transplanting seedlings into their permanent summer home, they should be gradually exposed to outside conditions. As long as daytime temperatures are above 60 degrees, place plants outdoors for a few hours each day, extending the amount of time as planting time is near.
If conditions for growing transplants and hardening off are not good, shorten their growing time indoors and transplant smaller plants directly in the garden. These are preferable to tall, spindling plants.