Originally Posted by Gariana
If it's a sword, tuck it in nice and deep, then pull it upwards gently until the neck of the plant and top of the roots are slightly out of the substrate. Swords don't like it when you plant them too deeply and will start to rot.
This is the best way to plant any of the rosette type plants-its important to keep the crown slightly above the substrate so it doesn't rot-Best to plant too shallow than too deep.
With the stem type plants-you can plant them deep, shallow or allow to float-with some of my stem plants I will let them float for awhile until they have roots then plant them-especially water wisteria leaves that I break off when I trim-a lot of the leaves will sprout roots within a week or so-makes it easier to plant IME.
You also have to be aware of Allelopathy, this is when plants cause other plants to die-I had this happen in one of my tanks I just setup a month ago-The hairgrass or spikerush (Eleocharis coloradoensis) can release toxic substance in the substrate and cause competing plants to die-Once I removed all the hairgrass the other plants stated to thrive-what a mess until I figured it out-Thank you Diana Walstad book on "Ecology of the Planted Aquarium"