My above described lemon from time-to-time has yellowing leaves and I can't discover why. I live in Denver. The following conditions prevail:

Tree is about 2 feet in height in large vinyl pot.
Pot contains drainage holes in bottm along with 2 inches of pea-sized gravel
Soil consists of standard, commercial potting soil
After watering, I lay tree on it's side to drain accumulated water out of base and away from roots.
I fertilize about every 3 to 4 months with a citrus tree fretilizer I purchased in Sacramento.
Tree is about 5 years old and has grown extremely slow for it's age.

Questions:

What about the yellowing leaves, good, bad or normal?
What am I doing wrong (if any) and what can I do to enhance the life and growth of this tree?

yellowing leaves BAD. first of all comercial soil is NOT good for citrus, even if you lay the pot on its side, that cant be good either. You need to get better soil and sooner the better. You may have root issues and if left to be, they can get a lot worse.

I would recomend using a good blend of peat with orchid mix, its easy to find. 3-1 ratio. It'll be truly well draining. you will see a big difference in how much water drains out vs potting mix.

check the roots, give them a light tug, if they pull apart, leaving little strings or just easily pull away, you have root rot I would rinse ALL soil off the roots to really check. then, if you notice, trim the roots till you get to healthy roots. the tree will not liket his and likly drop leaves. it will come back. to give the tree a bit of a break, trim a bit of the top leaves and branches off to comensate root loss.

You may not have root rot... yet. but in commercial potting soil, yellowing leaves.. you may be on your way. Its all the same issues I had to begin with. My mix held too much water, leaves yellowed and when I looked at the roots, they were almost gone. I lost 2 trees and recently a 3rd, it just never came back fully and died :( these trees are too expensive to have die and replace constantly.

Older leaves will turn yellow and drop as a sign of old age. Leaves that are not getting enough nitrogen will turn yellow and slow growth will result. Trees kept in soggy wet substrate will turn yellow as they can not breathe.

Citrus need a very well draining substrate that will allow for oxygen exchange. Citrus and most other plants breathe air just as we do. If we were to be kept under water for any length of time we would drown. This is what happens to plants in soggy soil. Even though it happens slower, the drowning still occurs. Pea gravel in the bottom of the pot is not a good idea either as it holds water in the soil.

Carefully remove the tree from the soil and check the roots. If they are mushy or dried looking they are dead and should be removed. If they are a light tan color they are alive and functioning. Rinse the roots in a solution of 1/8 cup chlorine bleach to a gallon of water if rot is found. If no rot is found rinse the roots in plain warm tap water. Re-pot in fresh well draining soil and place in an area that does not get direct sunlight for a week. Gradually move it into brighter sunlight over the next 2 weeks. If the tree looks worse in the sun than it does in the indirect sunlight then move it back.

You also may need a small fan to help dry the soil out since its all but winter where you live. Do not water until the soil has dried out considerably.
Hope this helps
Andi

I would not rinse in bleach! even a mild solution. if root rot is found, trim off the damaged areas and replant in fresh medium. I've yet to find any sites that recomend using bleach. Most of the big time growers on forums also higfhly discourage this. I've had this issue and with trimming, have had no issues again

The amount of bleach used will not hurt the plant. IF there is rot it is caused by a bacteria and it must be killed or it will continue to spread. The bleach solution is not for soaking but for rinsing. A swish and a rinse is all thats needed. No harm will be done to the tree. The harm comes when the mixture is too strong and used for too long. You can also just pour the solution through the pot and then rinse. I have done this myself and the tree suffered no ill affects. Infact the dying tree is now very much alive.

When I first read it my impression was a soak. But I can see how a light solution would help. It has also been recommended to use peroxide. there are also special liquids to use to flush soil.

Dont you love those 'dying' trees that come back to life? :)