Hi, 

We can't tell from the photo, is this still in a container? It looks like there is another type of variegated plant leaf with it maybe? Was this a pass along plant that maybe someone dig up some roots of something else? It looks to us like the 2 toned leaves and the stalks they are attached to are those of a Variegated Solomon's Seal, (Polygonatum odoratum 'variagatum'). 

The lighter green leaves look mostly like it is new growth on the Sweetspire (Itea) but also if its crowed in a pot with other plants, the nutrient issue could be corrected by planting it in the ground and separating those plants. The roots will be noticeably different. The Itea roots will be fibrous, while the Solomon's Seal are more rhizomes.  If you don't have a ground location for it to be planted, separating the plants and moving the Itea to a larger pot with fresh soil mix would be good. If you plan on leaving it in a container, you can mix about 50% compost and 50% potting mix for the soil media. You can use a slow release granular fertilizer that will help replace nutrients as they are leached out by watering. If you wanted a quicker fix, you can use a general liquid fertilizer (10-10-10 or 5-3-4) the next time you need to water.

Emily

You're welcome, happy planting!