Emergency personnel rushed to the scene on Middlesex Road at 6.10pm yesterday.
Two crews from Southsea and two from Cosham worked to extinguish the blaze – caused by a glass panel reflecting sunlight onto one of the sheds.
Crew manager Haswell, of Southsea Fire Station, said the flames spread across the outside of several properties.
He told The News: ‘The fire started from a garden shed and spread to trees, shrubbery, fences, and other sheds.
‘There were approximately six houses involved, with their gardens back to back next to each other.
‘It passed from shed to shed, and was a significant fire.’
Firefighters used six breathing apparatus and a hose reel jet to quell the flames, crew manager Haswell added.
He said the fire was not difficult to control, but was unwieldy and had devastated many outside buildings.
‘It was awkward that the fire had spread across the properties, so it was difficult to locate pockets of embers’, he added.
‘One of the sheds had a lean to on it, and the flames had gone onto the roof of that.
‘There was fairly significant damage caused to three sheds that were destroyed.’
The stop message was given at 7.56pm.
Crew manager Haswell said a glass panel used for a small allotment area had started the fire.
He added: ‘The sun was coming across sideways onto the gardens, and there was a huge glass panel over a small growing area, which reflected onto one the sheds outside.’