Regarding some kind of plants, I noticed that once the container become too small for the plant size, the new leaves are greatly reduced in size, altough there is still new growth.
What about citrus? The growth stops completely or what happens is something like what I described before?
I'm asking this because my lemon (grown from seed) is growing new leaves that are very small, but I have a few doubts on why this is happening...I repotted 1 year ago but maybe the tree filled again the new space available with its roots.
Or maybe it is more probable that this effect is due to a nutrition/ph/aeration problem?

Slide it out of the container and see...

That's what I call Pragmatism

Normally, when a tree becomes root bound in a container that is to small, the tree's growth begins to shoot straight up, much like toothpaste squeezed out of the tube. I know nothing of the content of your water supply, or how often you flush your tree's root system, but slow growth, and smaller leaf size frequently results from higher levels of salts in the root zone, such a carbonates, bicarbonates and etc. - Millet

Thanks Millet. I don't know much about my water, it is the tap water and I only know that it's ph is around 6.5. It is the water that I use for all the plants I have, included other 2 citruses (2 mandarins) that don't show such kind of problems. Maybe the lemon is very sensitive to water quality?
I water every 2-3 days in this period. With flush you mean a complete wash of the soil? I don't do it, do you suggest to give the soil a nice wash? Maybe it would be a good idea.
Just to give some more infos, the soil is a mix of clay soil, river sand and compost.
Thanks again, Ivan

It is important to flush your container at least 3 times a year, or more often depending on the quality of the irrigation water used. - Millet

Could there be a connection between salt stress and new growth on the lemon that is not purple or just slightly purple?

Salt stress effects every part of the tree, I am not sure. but I doubt that it has anything to do with the blooms color. - Millet

I have found that new growth on lemons & citrons will have very little purple coloration in the warm months. In the cooler months the new growth will be very purple in coloration.

Thanks Millet and Laaz! @Millet: I was talking about foliage growth, not blooms, but probably the mechanism would be the same

Ciao Ivano !

I think to wash out the salts from your soil cannot work, if you have clay in it.
You should have a well drained soil for that.

Best way I think is to have a well drained soil and use oranic fertilizer only.
By this you get no salt acumulation and the soil gets even better, for the organic fertilizer turns into compost.

Organic fertilizer = no salts???? OH please. - Millet

No salt = no salt

Oh yes !

You wish. - Millet