Underwhat condition does formaldehyde undergo aldol condensation

Dear Student,

Formaldehyde donot undergo aldol condensation as it doesnot have an alpha hydrogen. However, when it is heated with concentrated alkali solution, it gives a mixture of alcohol and the salt of carboxylic acid. This reaction is called Cannizzaro's reaction. It is a disproportionation reaction. 

$2\mathrm{HCHO} \stackrel{\mathrm{NaOH} }{\to } {\mathrm{CH}}_3\mathrm{OH} + \mathrm{HCOONa}$

However, it can show cross aldol reaction where it reacts with another aldehyde or ketone having alpha hydrogen. 
Formaldehyde also show polymerisation in presence of lime water i.e. Ca(OH)₂ which leads to formation of a sugar called formose.