preventing dead in middle of conifers

i have many different cultivars of conifers--from cryptomeria to thuja-- they are in containers and tend to have dead in the middle of the plants---this is especially prevalent in the spring as they come out of their winter dormancy---any ideas as to what causes this and what preventive steps might be taken

 

Oldest leaves dying and falling out an annual event, not to be avoided. Sparseness that allows this to be more visible can be addressed, by providing better growing conditions.

 

Yes, also blowing the dead stuff out with a hose or something instead of just letting it hang there.

 

If you prune these plants so that light can get into the centre of the plant and if its not too old you should get growth on a more even basis. Air movement through the plant will help prevent some general health problems.

 

The plant opening up on its own is what makes the spent inner foliage visible. Pruning to open up the center will just make it more visible. Some kinds just open up with age, others become sparse if conditions are less than optimal. In pots there might be problems with leaching of potting soil or sometimes getting dried out between waterings, or potting soil having decomposed and become mucky - making potted specimens more scraggly that same kinds might be in ground.