Readers silk tree in excellent shape in rock mulch Q. I have a mimosa tree and I am giving it a lot of TLC and it seems to do well here. A. Your Mimosa or silk tree looks great and is doing well judging from the picture you sent to me.  It looks like it has good growth and a nice dark green color.  You must be giving it a lot of attention as it seems to be thriving there in rock mulch.  I will caution you that these are not long-lived in our climate and tend to suffer a lot of branch dieback or decline as they get older.             They particularly struggle in rock mulch that is fully exposed to summer extremes.  They seem to live a bit longer when surrounded by grass rather than rock mulch.  It has never been diagnosed, to my knowledge, but this decline may be mimosa wilt disease, a disease that infects and plugs the vascular or water transporting system in the tree.  Crape myrtle 20 years old growing in alkaline pH 8.2 soil with little soil amendment  following regimen suggested here. There is some wood mulch at the base of the tree in the irrigation well.             Continue to keep it healthy and it’s possible to keep it going for quite a while.  Another plant which can suffer here in rock mulch is crape myrtle but is, in my opinion, a better tree for here if you give it some TLC like you are doing.  With this tree you can keep it looking good growing in desert soils by fertilizing it with a well balanced fertilizer like 16-16-16 in late January along with iron chelate applied to the soil and watered in.              Follow this about two months later with a liquid fertilizer applied to the leaves until the solution begins running off the leaf surface and dripping onto the soil.  I usually apply a wetting agent with the liquid fertilizer applied to the leaves.  If you can keep plants healthy, they can withstand diseases and extremes of temperature and soils better