These dendritic crystals that you see on the wall may be formed by a rapid evaporation of the solution the goes up to the wall by capillarity. 

The crystal you want will grow from the solution. If you have one crystal of the same material, add to the solution. Take care to add one or at least very few crystals. 

change the cooling rate. Dendrite formation is sensitive to many things including cooling rate.

In the paper of Mullins and Sekerka (http://dx.doi.org/10.1063/1.1702607) they derived stability criteria of regular/dendritic growth of crystals.  This criteria depends dramatically on oversaturation of the solution. The main idea is that in high oversaturation of solution only dendritic growth is possible.  When you evaporate too fast, oversaturation grows so high that dendritic regime starts.

So, main advices are:

1) Try to evaporate slower

2) Take lower initial oversaturation of component, which you are trying to grow as a crystal

3) If you have, add some crystals of the same component (as Silas said), they will grow consuming your component from solvent, so it will help to retain low oversaturation during evaporation, and by the way, later you can use this grown crystals in X-Ray study.

4) The crystals are growing now on the walls. One possible  reason, is that you have wetting vessel, so there is a meniscus near which equlibrium concentration of your component in solvent is not the same as in the bulk solution. So nucleation of crystals is fasters near meniscus. May be use of another vessel made from non-wetting material will help (or vice versa).