It depends on the soil mix in your containers and whether or not your containers have drain holes in them.

If you are using a fast draining mix, such as the gritty mix, and your containers have proper drain holes, then the salts will leach out easily.

If you are using a heavy mix with components like peat and compost it will not leach as easily and the salts can easily accumulate.

Of course if your containers do not have drains, then the salts will accumulate regardless of how well draining the soil mix is.

Hope that helps.

Many times gardeners, especially with house plants will not use enough water, when they water, because they do not want water coming out the drain. A build up of salts is inevitable in that case. Every time you water about 20% of the water you use should be seen coming out the drain. Al