From reading your post it sounds to me like you already suspect your growing mix as the culprit. Do the buckets have drainage holes? What is the purpose of the rocks?

Agreed - the bottom of your containers are probably very soupy and full of anaerobic bacterial nasties. Root metabolism and water nutrient absorption slows to a limp and then a crawl when the roots are deprived of adequate air. so ...... "Is there a reason to replace ALL the soil every year?" I think you're probably dealing with it.

The rocks just raise the level of saturated soil higher in the container, so while they may be effective at reducing the amount of soil you use, they surely do not help improve drainage.

Unless you have burned leaf tips/margins on the Impatiens foliage, it's not over-fertilizing. I would normally tell you to insert a wick in the drain holes & allow it to contact the earth of dangle below the containers, but the layer of rocks probably negates the effectiveness of that saturation management ploy, but you could still try it. If you search the words tapla wick drain hole you'll come up with lots of commentary on wick usage and soils.

Al

Yes, as stated when I originally set up the planters they all had drainage holes. The idea they have plugged up is making me think. They definitely do not need the amount of water they did when this all began nine years ago, but they never fill up with water either. No brown spots. I see there is a thread on re-using soil. I will read that and go from there.

I didn't miss that point - I only mentioned drain hole as part of an intended search so you could learn about wicks. ;o) Good luck - come back if you have additional ?s.

Al