light chart for growing weed

Light chart for growing weed

Light intensity is one of the main factors that can indirectly affect VPD as it can increase or reduce the plant’s temperature. Higher temperatures lead to more VPD content.

To learn how to control VPD, you first need to understand its effects on your plants’ growth.

A Vapor Pressure Deficit, or VPD Chart is a proven tool that can maximize your desired results when growing in a controlled environment. Our vapor chart suggests optimal ranges to run your plants during the different stages of growth.

It’s recommended to get bulbs with a higher intensity from the start. That’s because it’s easier to reduce intensity than it is to increase it. What’s more, higher levels lead to denser plants with higher yields.

Finding the Right VPD for Each Growth Stage

Dialing in a proper VPD in your grow will help to reduce issues brought on by either too much transpiration, aka high VPD values, or the plant’s inability to transpire enough, AKA low VPD values.

Cannabis at the vegetative state is hardier than a baby plant; hence, it can withstand higher VPD concentrations. Generally, aim to slowly raise the VPD throughout this stage until it tops at 1.0 kPa. Note that CO2 absorption is vital here, so try not to increase your VPD dramatically.

The stomata are the first area of the plant where you’ll notice a change. Higher VPD will cause the stomata to constrict to prevent excessive water loss. As a consequence of smaller stomata, the amount of CO2 the plant absorbs reduces as well, which will directly affect photosynthesis. Thus, adjusting VPD will enable you to fine-tune this process.

How Does VPD Affect Cannabis Growth?

Lastly, the flowering stage can withstand higher VPD but requires lower humidity. Slowly raise the VPD from 1.0 kPa until it hits around 1.4 kPa.

The key to calculating the right VPD is to check the growth stage of the plant. The plants are relatively fragile at the clone or baby stage, so they can’t handle too much stress. They also need higher rates of nutrients to compensate for their underdeveloped roots. So, as a rule of thumb, aim for a VPD range of around 0.5 – 0.7 kPa.

Light chart for growing weed

Most indoor growers give their cannabis plants 18-24 hours of light a day during the vegetative stage. The exact number of hours needed to keep a plant in the vegetative stage is dependent on the strain, but 18+ hours/day will keep basically all cannabis plants in the vegetative stage.

If you're growing a cannabis plant grown from a random seed ("bagseed"), unless you somehow have an auto-flowering seed, you will need to understand about cannabis life stages and how they are affected by light periods.

You do this by changing your light so that it only shines for 12 hours a day, and the other 12 hours a day your marijuana plants are kept in TOTAL darkness.

Light chart for growing weed

Cannabis is a "photoperiod" plant, which means the amount of light received each day decides when the plant starts flowering or making buds. This article explains how much light a day your photoperiod cannabis plants need to grow and start budding, so you get to a happy harvest day. What about auto-flowering strains?

So indoor growers have a choice to flower their plants whenever they want… When is the best t ime to start flowering your cannabis indoors?

Cannabis will stay in the vegetative stage as long as the plant gets short nights (less than 11-12 hours of darkness each day)

Outdoor growers wait until their cannabis plants start naturally flowering on their own, usually after mid-summer when days start getting shorter than 12 hours.