JARS v54n3 - Seedling Portability for Maximum Growth

Seedling Portability for Maximum Growth
Dr. Mark Konrad
Sewickley, Pennsylvania

Maximizing seedling growth during the first year often involves a major intellectual exercise. Those who succeed have usually learned how to run a formidable obstacle course. To have a modicum of success, many parameters such as light, humidity, timing, medium, water, nutrients, and temperature have to be just right for continuous growth.

A major source of continuity is lost without a greenhouse, which is highly important during the first year. To compensate for this I have found it necessary to have a flexible program whereby the seedlings sewn in the fall are moved from indoor lighting to the outdoors; and then they are moved back under the lights, all in the same year to get substantial growth during their first year.

Flats with containers for convenient seedling 
Flats with containers for convenient seedling portability.
Photo by Mark Konrad

A significant impediment to success is often the transition between indoor-outdoor culture. Those of us in colder parts of the country such as southwestern Pennsylvania have limited options without a greenhouse.

Since frost can occur until the end of May, there is a very narrow band of time for the seedlings to become acclimated. By the middle of July, there is a decreasing amount of outdoor light signaling a decrease in growth potential.

To work around this dilemma, the following options can be considered:
1.  Seedlings started in the fall under indoor lighting are moved to the outdoors by the last ten days of May or sooner if protection can be given. Leave the seedlings outdoors until the end of July and then return them to indoor lighting for August and September. The seedlings are again returned to the outdoors October 1st to be hardened off in a cold frame.
2.  After returning to indoor lighting at the end of July the plants can be left in place for a second fall and winter.
3.  Planting seeds every other year might be a third option with the consideration for quality over quantity.

To make the method feasible, plants should be in a highly portable state, i.e., flats filled with potted plants. If the system is highly organized, the whole operation can be very simple.

Comment: These suggestions are the result of an area of seedling culture which may have not been given enough attention in the past. Proper timing and the planning for maximum growth during the first year can help avoid countless failures in rhododendron seedling culture.

Dr. Konrad is a member of the Great Lakes Chapter. He is a frequent contributor to the Journal.