Leslie is correct...they are making increase....they only bloom on *new* increase, and if they aren't making very MUCH increase.....do a soil test. My guess is you need a little more fertility. barring that....and if the sun *exposure* hasn't declined do to trees growing larger....my only other guess would only apply if you are using a pre emergent weed control....like Preen. If you use *too much*, it can inhibit root growth , even on established plants, and that , I would think, would cut down on increase. If the soil test shows the N-P-K to be sufficient, and the ph is right, it still *could* be trace mineral deficiency .....try using a foliar fertilizer....like Miracle Grow...they usually have some 8trace elements* not found in the bags of "10-10-10".(or whatever you use)
