There are two major methods of containerized seedling production: unheated production in cold frames and production in heated greenhouses. Harrington Tree Nursery enjoys the benefits of both. The tree nursery operates from mid-March to mid-November.
A cold frame is similar to a greenhouse but is not equipped with a heating and automatic venting system. Each cold frame may hold from 70,000 large seedlings to over 300,000 small size seedlings. Crops are grown from April until September. Dormancy induction and frost hardening are done naturally at the end of the season. The snow insulates the seedlings and protects them from frigid winter temperatures. The cold frame production system takes two years from seeding to planting.
The production of forest seedlings in greenhouses requires a significant investment in greenhouse infrastructures. With these heated greenhouses, it becomes possible to grow two crops of seedlings per year. If seeded in March, a crop can be ready for planting by early June of the following year. A second crop can be seeded in June immediately after the first crop is placed outside in shadehouses. The summer crop is grown and hardened-off inside the greenhouse. The seedlings are then taken to an outdoor holding area for the winter and ready for planting the following summer. It takes 14 months to grow a “ready to plant” seedling in a greenhouse.
At Harrington, greenhouses are heated with a bi-energy system: two electric furnaces, plus two oil furnaces. The two systems can work separately or simultaneously. Uniform and reliable heat is supplied through air exchangers located in the middle of each bay under the growing tables in greenhouses. In case of power failure, a generator starts automatically to keep the oil burners going, as well as pumps, lights and other domestic utilities.