Probably needs Iron or if it is stunted then Nitrogen.

Here is a link that might be useful: Propagating Perennials

Yellowed leaves can have many causes - ranging from normal die-off of old leaves, iron chlorosis, thrips or other insect pests, over-watering, under-watering etc., etc..

First, you need to find out WHY the leaves are yellowing, and only then apply remedies.

Can you post a photo? If not, take some of the leaves to a GOOD nursery - if you get a kid who immediately says to spray with such-and such a product, get another opinion, sine the kid may or may not (more likely) be right. You can also take the leaves to your county extension agent - if s/he doesn't know the answer, the leaves can be sent to your state univ. lab for tests.

Is your plant stressed? Is the soil acid enough? Is it in too much sun? Is the soil too dry? Common causes of stress in Pieris (Andromeda).

I am also having problems with my Andromeda's leaves yellowing out. This does not happen quickly and I am thinking it may be insect related.
I am going to try and upload some pictures of the damaged foilage to see what anyone may think to help identify the culprit.

I’m also having an issue with my andromeda in the east side of the house under big oaks. just this year. have been using neem oil i see the spider mites. was doing well and now the leaves are yellow and falling g off however i have new beautiful growth down below. I raked mulch and any moist areas and see how that works in a day or two. Than i’ll try hollytone. Any advice is appreciated