Lamps for indoor growing of auto-flowering plants: which ones to use?

Which lamps should be used for indoor growing of autoflowering plants?

Modified on: 20/09/2022

Are you curious as to which lamps are most suitable for the proper development of auto-flowering plants? Here is the answer

The previous article talked about the photoperiod, photoperiodic plants, and how important it is to respect particular light and dark cycles to encourage their development.

This article will focus on auto-flowering and dwarf auto-flowering plants, i.e., hemp plants that reach the flowering stage even though their light cycles remain unchanged.

What might be the best lamps for indoor growing of auto-flowering?

What are the tricks of the most experienced hemp growers?

Here are the essential facts on the subject.

Hemp lit with LED lamps

Growing autoflowering hemp plants indoors: lamp tips

Autoflowering, cannabis begins to flower after a certain period, regardless of the variation in light and dark cycles. However, this does not mean that plants born from auto-flowering seeds can live in darkness; all hemp genetics depends on light for the process of photosynthesis.

If you’ve ever wondered which light is best for the optimal development of autoflowering plants, as with photoperiodic plants, the answer is undoubtedly the sun. However, you can create the perfect lighting for vigorous plants and full buds, even indoor cultivation.

Let’s see how.

To cultivate auto-flowering plants, you can use a single light source for the duration of the plant’s growth. Alternatively, you can alternate between different light sources as you move from germination through the vegetative phase and then into flowering.

The ideal lights for the entire life cycle of auto-flowering plants are broad-spectrum LEDs. These lamps are undoubtedly expensive, but they perform impressively and have lower running costs than older lamps (such as HID or xenon lamps).

Since auto-flowering hemp plants have a very short vegetative phase, some hemp growers prefer to use HPS (sodium) lamps, which are orange/red light sources.

Hemp growers who like to follow every step of plant growth, on the other hand, tend to use:

  • for newborn auto-flowering plants (germination): compact fluorescent lamps (CFL);
  • for plants in the vegetative stage: blue light bulbs (6500K), which are perfect for stimulating the growth of the plant in terms of density;
  • for plants in the flowering phase: HPS lamps with red light are ideal for the flowering stage as they stimulate the production of larger, more compact buds.

Read also: Plant photoperiod: what it means

What is the best light schedule for auto-flowering?

Auto-flowering hemp plants can survive even when exposed to just six hours of light. However, more exposure to light sources will ensure a better yield and allow the grown specimens to become more robust and vigorous.

Hemp inflorescence illuminated by a lamp

So, what is the appropriate formula?

Let’s find out the differences between the three main programmes used:

  • 24/24 programme
    Some hemp growers claim that providing their autoflowering with non-stop light (24 hours a day) allows them to maximise their growth during the vegetative phase. This programme optimises the final yields and does not require a timer but involves a considerable energy expense.
  • 18/6 programme
    considering that the vegetative phase of autoflowering plants is relatively short, providing them with light for at least 18 hours will allow them to develop a healthy and robust structure. At the same time, the six-hour break will enable the plants to recover their energy (for many cannabis growers, this is essential for obtaining quality harvests). This programme guarantees excellent yields and involves much less energy expenditure than the previous one. To get the most out of it, you need a timer.
  • 12/12 programme
    this last programme is undoubtedly the most economical; however, it will produce smaller buds and a lower yield than the previous two cases. If you wonder why some hemp growers choose to use this programme, it’s because it avoids heat stress and it allows you to grow auto-flowering plants alongside photoperiodic hemp plants.

As you can see, each programme has both pros and cons, and it is up to each cannabis grower to decide which one to choose, depending on their needs and means.

Read also: Harvesting autoflowering: do pistils give the signal?

To conclude

In the previous paragraphs, we have told you the secrets of experienced cannabis growers regarding choosing lamps for autoflowering plants. In addition, we have outlined the pros and cons of the leading lighting programmes, so you should have a pretty good idea of what to expect.

We want to remind you that this article is for information purposes only and that growing cannabis is still forbidden in Italy (unless you have official authorisation).

That said, if you are fascinated by the world of hemp and love collecting marijuana seeds from the best genetics, visit our online store: You can choose between feminized, autoflowering and fast growing weed seeds in our shop.

What are you waiting for? Explore our e-shop today. See you soon!