A question that often comes up, is when to transfer seedlings into their permanent home, whether it be to a soil-based or to a hydroponic grow system.
This depends on a few things: 1-the type of plant, 2-the container used to start the seed, 3-where you are transplanting to, 4-how much time you wish to spend nurturing growing seedlings.
In their excitement, people sometimes transfer their seedlings as soon as they see a leaf or two. You need to wait until at least the first or second set of true leaves appears. (The very first ones up are not true leaves). Some people advise waiting until the plant is 4-6 inches tall.
If your container is very small or crowded, you will need to move the seedlings sooner. For example, seeds started in an egg carton will quickly outgrow their container. (This can be a great choice if you plan to transplant outdoors into soil as most roots will push right through the paper variety).
Seedlings need to be monitored and tended in order to ensure that they don’t dry out. As they grow, this is even more imperative as they consume more water.
However, you should be able to see good root development prior to transferring the seedlings. If you do not and you transfer the seedling too early, the root will become saturated and growth will be stunted. A little bit later than sooner is a good rule to use when transferring seedlings. Just make sure to give them regular attention so your efforts aren’t wasted!