Autoflowering’s early flowering: when and how long does it last?

When does autoflowering start to bloom, and how long does it last?

Published on: 25/05/2021

The start of flowering of autoflowering cannabis in full detail

The period from germination of cannabis seeds to the start of flowering of autoflowering plants is a time-consuming time for growers, who must take care of the plants carefully for the quality of the buds to be excellent.

However, there is a significant advantage over “regular” plants. These depend on the photoperiod (i.e., the hours of light and dark received) begin to germinate when the hours of uninterrupted darkness prevail over the hours of light.

Auto flower seeds plants, on the other hand, germinate according to their age! It means that the grower does not have to worry about creating darkness for the seedlings to bloom: they will start to sprout automatically (which is why they are called “autoflowering”).

At what age do automatic cannabis strains start to bloom?

The initial stage of autoflowering flowering

Autoflowering starts spontaneously when the plants are about 3 or 4 weeks old, immediately after the vegetative stage.

This type of cannabis has a speedy growth. It is usually ready for flower harvest after about 13 weeks (3 months) from the germination of the autoflowering seeds.

The reason for this peculiarity lies in the origins of automatic flowering cannabis: in its genes, there are those of Ruderalis cannabis, able to survive even in hostile temperatures (it is born and grows even in Russia …), with very short summers and very long winters.

How can a plant survive in these conditions?

Buy adapting and reproducing even during periods of darkness, not developing high and devoting little energy to the production of cannabinoids, terpenes, and flavonoids.

Since the latter characteristics are not very advantageous for marijuana producers, but wanting to maintain resistance and automatic flowering, Ruderalis was then crossed with Indica and Sativa varieties of cannabis to give life to a new type (the autoflowering) with these distinctive elements:

  • Auto flowers seeds depends on the age of the plant and not on the hours of light and darkness it receives;
  • high THC content;
  • medium or low height (in the case of dwarf autoflowering plants), perfect for indoor cultivation;
  • rapid growth;
  • high resistance (without exaggerating) to low temperatures, wind, humidity, and moulds.

Despite having Ruderalis genetics, strains born from the best autoflowering marijuana seeds produce large, dense, cannabinoid-rich flowers!

Read also: Autoflowering pruning: is it safe to proceed with defoliation?

How long does it take from the start of autoflowering flowering to harvest?

Autoflowering plants usually mature much faster than photoperiod plants, so much so that they are ready for harvest after 2 or 3 months after germination.

It means that about a month passes from the beginning of flowering to the time of harvest, but the laziest plants may take a few more weeks to develop fully.

During the first few weeks of flowering, the plants continue to grow tall even as buds are forming. Shortly before harvest, however, the stems stop growing to ensure that the flowers have all the energy they need to develop.

In the last weeks of flowering, the buds grow drastically, becoming very heavy… of course, only the plants get the proper care!

What do growers do to promote the excellent development of cannabis flowers?

Between the vegetative stage and the start of flowering of autoflowering plants, growers continue to provide reasonable amounts of fertilizer to the plants (for about a week). Usually, these fertilizers have 5% nitrogen, 7% phosphorus and 10% potassium.

Fertilized cannabis flowers

In the middle of the flowering phase, they begin to supply the plantation with fertilizers with different percentages NPK (nitrogen N — phosphorus P — potassium K), i.e., 5% nitrogen, 10% phosphorus and 15% potassium.

During the last weeks of flowering, it is necessary to reduce the percentage of nutrients, switching to a fertilizer with 4% nitrogen, 7% phosphorus and 10% potassium.

About a week before the flower harvest, many growers perform root rinsing, called cannabis flushing, consisting of rinsing the soil (and therefore the roots) with neutral pH water.

The goal is to prevent nutrients from remaining in the flowers (it seems they can compromise their flavours and aromas).

Read also: Defoliating autoflowering plants: when is it appropriate and why it is done?

How to know when the flowers are ready for harvesting?

The most accurate technique to understand when cannabis flowers are ripe is the one that involves observing the trichomes with a magnifying glass.

As you may know, trichomes are resin-producing glands rich in cannabinoids, terpenes and flavonoids, and they take on different colours based on the flowering week.

They are initially transparent, turn milky and finally take on an amber or honey colour. The perfect time to harvest is when almost all trichomes are opaque and milky, and only a few are amber.


Now you know precisely when the autoflowering phase begins, how long it lasts and when to understand that it is time to harvest the ripe flowers.

But be careful: remember that it is not allowed to grow cannabis in the UK, not even for personal use (cultivating it for personal use is an administrative offence, while growing marijuana for distributing it is a criminal offence).

However, it is legal to buy weed seeds online to collect them because if they don’t germinate, they cannot produce THC.

Do you want to buy collectable seeds of excellent quality, produced by the best seed bank (BSF Seeds) and good discounts on volume?

Then visit our Sensoryseeds shop now! We are waiting for you.