It would be highly unusual for any rhododendron grown from seed to be ready for outdoor planting in less than three years. When yours are large enough, plant into individual pots, keep moist but not sopping with distilled water or rain water. Fertilize with 25% strength soluble fertilizer every 3-4 weeks. Plan on keeping them indoors under lights or in a cold frame for the winter.

Thanks -- They seem way too dainty to put outside right now!

Here is good advice from Allan and Shirley Anderson of NJ:

When weather permits and natural days become longer the flats are placed outdoors in a moderately shaded area. Supply with one-half strength soluble fertilizer and water as needed to prevent drying. The seedlings will grow through the summer. We stop fertilizing about the middle of July, and in the fall we transfer the 3 to 6-inch plants into individual containers for winter protection under plastic. In earlier years we left the seedlings in the original flats and wintered them over in cold frames for planting out in the spring.

At this point seedlings are much like other small plants such as mericlones* or rooted cuttings. They will still need some protection outdoors from wind and too much sun. Windbreaks and partial shade from high trees or snow fencing, etc., are described in many books.

Whether you want to try a few or many, the growing of rhododendron seeds is great fun and an absorbing pastime. We recommend it!

*At this stage of growth the seedlings may be handled as if they were rooted cuttings or like the mericlone propagules sometimes sold at plant sales and supplied by tissue culture labs.

[I would add to protect from heavy rains when they are outside.]