I did a spring grow last year and it turned out to take way too long. The problem was that we just tried to let them naturally bud. But as the days get longer they started to veg again. What you need to do is get a sheet of plastic that is black on the inside and white on the outside from a grow shop. Then light dep the plants to get them to bud and stay budding. It is cheap and will get the job done. Put the white side out to reflect the heat of the sun and the black inside to block any light.

Mine took so long last year that I had to axe them at the end just to proceed with the regular summer crop. They were OK because I did not have any other smoke but paled in comparison with summer weed.