Any chance of a picture? Sometimes the very outer leaves go yellow and start browning but I just pull them off and they still grow.

We either need a pic or more info - like, are they in a pot or the ground, how long have they been planted, in sun or shade?

if they are last years leaves just pull them off if the new ones then have they had weedkiller drift on to them? has the soil/plant had any fertilizer added? often a dose of Epsom salts cures most yellowing problems as it is caused by a mineral deficiency.
welcome to GoY too.