I'm building a raised bed garden for my lettuce, collard and kale. The structure is not quite complete, but I've started the seedlings in rapid rooter plugs in a plastic tray. It sits outside growing under shade cloth in partial sun. The collard and kale seedlings have great color and new growth, but the lettuce seems to heading downhill. The "oldest" of the lettuce seedlings were a very pretty light green, but recently they have been slowly losing color and some are a pale whitish color now. Have they outgrown the rapid rooter plug and plastic tray? Should they have been transplanted into the potting soil mix weeks ago?