The chemical garden relies on most transition metal silicates being insoluble in water and colored.
When a metal salt, such as cobalt chloride, is added to a sodium silicate solution, it will start to dissolve. It will then form insoluble cobalt silicate by a double displacement reaction. This cobalt silicate is a semipermeable membrane. Because the ionic strength of the cobalt solution inside the membrane is higher than the sodium silicate solution's, which forms the bulk of the tank contents, osmotic effects will increase the pressure within the membrane. This will cause the membrane to tear, forming a hole. The cobalt cations will react with the silicate anions at this tear to form a new solid. In this way, growths will form in the tanks; they will be colored (according to the metal cation) and may look like plant-like structures.
The usual upward direction of growth depends on the density of the fluid inside the semi-permeable membrane of the "plant" being lower than that of the surrounding waterglass solution. If one uses a metal salt that produces a very dense fluid inside the membrane, the growth is downward. For example, a green solution of trivalent chromium sulfate or chloride refuses to crystallize without slowly changing into the violet form, even if boiled until it concentrates into a tarry mass. That tar, if suspended in the waterglass solution, forms downward twig-like growths. This is because all the fluid inside the membrane is too dense to float and thereby exerts a downward force. The concentration of sodium silicate becomes important in growth rate.
After the growth has ceased, the sodium silicate solution can be removed by a continuous addition of water at a very slow rate. This prolongs the life of the garden.
In one specific experimental variation, researchers produced the chemical garden with a single growth "tube".