Q.1- I am growing romaine lettuce and kale indoors from seeds under the light, before I put them outside in the plot if weather permits. when the seeds germinated the leaves appeared on a long and quite thin stems that are not capable of holding up straight the bunched-up leaves. Are the stems and the lower part of the bunches to be buried in the growing medium and also later in the soil in order to keep them vertical?
Q.2- When the Amaranth seedlings appear they are so tender that they fall and die after even a light spray of water is used. What is the proper way to keep them hydrated? should they be moistened from underneath?
Q.1: For your romaine lettuce and kale, the transplanted seedlings should be set perpendicular to the ground (that way, they will grow straight) and placed deeply enough in the soil that they are well-supported. However, they should not be planted any deeper than the base of their first leaves. Remember too that you can direct-sow the seeds in the garden throughout the growing season.
Here are a couple of helpful links: Utah State University’s Kale in the garden provides a good overview of how to grow kale from seed or transplants. The university’s Lettuce in the garden includes practical information about growing lettuce.
Q.2: I located no helpful literature concerning the best means of watering amaranth seedlings. As you indicate that a light spray of water seems to cause the seedlings to die, then spraying or moistening the soil around the seedlings may be preferable.
Amaranth is a warm season crop that requires full sun and like kale and lettuce it can be directly sown in the garden. Best germination occurs when the soil temperatures range from 18-24°C. For Canada this usually means a late May or early June planting. Seeds of Amaranth should be sown no more than 1/4″ deep. The following is an excellent article with detailed information on starting Amaranthus seedlings indoors as well as sowing seeds direct: Growing Amaranthus