The depth (height) of the tank should be considered when selecting plants, as some will not do well in deep aquariums. Some species of plants likeVallisneria gigantia can grow leaves over 6 ½ feet (2 m) long. In shallow aquarium, Vallisneria gigantia leaves would quickly grow to the surface and block out light.
Laterite is clay soil rich in iron, and is usually a red color. Most plants need iron to thrive in an aquarium. Laterite can provide long term constant source of iron to rooted plants. Sand substrate is the best when laterite is used, as it will help keep it under the bed.
This planted aquarium has laterite in the bottom half of the substrate to provide iron to the roots of the plants.
Laterite is typically added to the bottom half of the aquarium substrate. First wash out the substrate for the aquarium, then mix one half of the substrate with laterite. Lay this laterite rich substrate on the bottom of the aquarium and then cover it up with clean substrate. After all the substrate has been added to the aquarium, lay a plate on the substrate, and pour the water into the aquarium on top of the plate, taking care to not to disturb the substrate. The aquarium will be a little cloudy for a few days until the fine sediment is filtered out or settles to the bottom.
If your aquarium is already set up, there is an alternate plan you can take to add the laterite to the gravel. First mix the laterite with a little bit of water until it is muddy. Draw the watered down laterite into a large syringe or turkey baster and inject the mix into the lower level of the bed.
The disadvantage of using laterite is when you pull plants out of the bed, you will usually bring some laterite to the surface. For aesthetic reasons, this is undesirable.