It depends on the type of plant that your trying to trim. Any plant in particular your asking about?

 

Stem plants are the easiest - cut them where ever you wish and leave the bottom part in place, or remove and toss it, and plant the cutoff part. Today I found some loose leafs of willowleaf hygro that were floating in my tank, growing a mass of roots at the base of the leaf. Plants like that almost defy you to stop them from growing. And, that is why so many easy to grow plants are bad nuisance plants if tossed into any natural body of water.

 

I agre, and you would mostly cut at the base on most not all plants, then some plants can be cut in a sideways manner just to cut the yellowish' or dead parts and they will grow back, it is best to research the plants you have and want to trim, so you will know there growing habits, and which way the grow best being trimmed.

 

everyone seems to have there own opinion on cutting/trimming plants. plants like amazons or large leafed plants are best to be cut nearest the root. as for stem plants they are to easy just pinch off or cut off. i have several steam plants that get to high and i just cut them right above a leaf and let the short cut top float at the top for a day or so lto let the roots start good again ad then put backin substrate. i have also heard that vals can live if there cut off at the top then i hear no cut at the base not in the middle of the leaf. whos right? who knows? even the books are all different lol