CFL Flowering Time: Do CFL Grow Lights Take Longer Than HIDs?

how long to flower under cfl


Have you heard the myth?

“CFL flowering time takes longer than flowering Cannabis plants under HPS lights.”

Contrary to semi-popular assumption, there is NO empirical data or PROOF that plants flower longer under CFLs than high intensity lighting such as HPS or Metal Halide lighting setups.


I’ll repeat:  There is NO empirical data or PROOF that plants flower longer under CFLs than HID lighting.”


So if these so-called myths aren’t true, how did they come about? Surely, you say, there must be some truth or reasoning behind the assertion that CFLs take longer to flower than HIDs, right? NOPE. There isn’t. Let’s explore why….


1st Many people use CFLs incorrectly, with either far too little wattage, or far too  little intensity; or just terrible placement of the bulbs, which provides their plants with FAR less light than an HID would give. Of course–resulting in delayed onset of bloom or “late” finishing (prolonged).


2nd Many whom use CFLs go by the breeder / seedbank’s estimate of flowering time, and don’t think to add another week or two to the total flowering time, or even longer. Since the breeder could based their “average” flowering times on variables which differ significantly from your own, in other words their experience and conditions may allow their plants to flower and ripen quicker than the same strains would in your environment and in your care.

So always assume that the plant MAY take 7-14 days or longer to FINISH flowering than the time quoted by the breeder and/or seedbank, so add at LEAST 7 days to their estimated time, and then harvest based on RIPENESS and/or trichome color– whichever you prefer.


3rd Many who use CFLs don’t take into account the time it takes for a plant to start flowering, after switching to 12/12 (bloom schedule). This MAY be a factor to be considered when growing your strain with CFLs, depending on various factors. If you grow the same strain more than once, you’ll learn how long it takes to flower once the switch to 12/12 has commenced.

If you grow different strains every run, perhaps expecting a 7 to 14 day delay before the start of flowering is a good general rule. This will be the same  regardless of what lighting system you use, as long as the RIGHT lights are placed correctly.


4th Lumens are lumens and watts are watts. How much the light diminishes as it travels  certain distance is what will determine your results. Many growers who experience flowering times that are much longer than those quoted by the breeder/bank, are giving their plants far too little light.

It’s also possible that the reflection characteristics of the grow area are nil and more light is bouncing/escaping than is being absorbed by the plants. This will definitely cause a delay in finishing as well as the telltale “stretching to the light” syndrome, even after the first 2-3 week “stretch.”


By Robert Narley