Help, my weed is already flowering! All about Early Flowering of Weed

It's mid-June and you walk into the garden in the morning for a routine inspection of your weed plants. What is this? They are already flowering!? It can just happen that your weed starts flowering too early. Even if you don't have auto flowering weed seeds. We have sent this question to the master growers of our seed suppliers and received many different answers. In this article we explain everything there is to know about early flowering and the start of flowering of your weed plant.

In this Article

  1. How much light does a weed plant need?
  2. Sativa and Indica
  3. Flowering time of the weed plant
  4. Weed is already blooming - Causes and Consequences
  5. Advantages and disadvantages of Early Flowering
  6. Re-veg - Reintroducing the growth phase
  7. Growing Calendar for Growing weed outdoors
  8. Promoting flowering of the weed (putting it in the dark)
  9. Selection of Notorious Early Flowering Weed Seeds

How much light does a weed plant need?

Let's start at the beginning. How much light does a weed plant actually need? If we zip up the grow room behind us for a moment and step outside into the pleasant summer weather that outdoor plants appreciate so much, then we can learn something about light. 

In this article we are discussing photo period weed plants by the way: the classic weed plants without auto flowering genetics. Whereas auto flowers seamlessly transition into flowering after a short period, most weed plants need a change in light/growth schedule.

First of all, the sun does not shine 24 hours a day in the places where weed plants have evolved. Both tropical sativas and indicas from the mountainous regions of more temperate regions will only flower when the days get shorter. The intensity of light also plays a factor. What does 'darkness' actually mean for a weed plant?

Sativa and Indica

There is a difference in the place where weed plants originate from. Sativa weed plants come from tropical areas near the equator. The sun in these regions stands high in the sky for a large part of the year. Therefore both the light intensity and the growing season are long. You will notice that the light is strong there if you walk around unprotected: you will get sunburned in no time. Around the equator, day and night lengths are also the most equal. That is why sativas are less sensitive to changes in day/night length. 

Pure sativas, but also sativa-dominant hybrids, can even bloom without you changing the growing schedule. This has everything to do with their genetics and the fact that the day and night lengths from the area where their ancestors come from remain practically unchanged. On the other hand, sativas grow more slowly and have a longer flowering period.

 Indica weed (left) and sativa weed (right).

If you travel further north from the equator, towards the northern regions of India, Nepal and Afghanistan, you will find weed plants with much broader leaves. These are the indica weed plants, which have evolved under a more variable climate. Because winter can be especially harsh here in the mountainous regions, indica plants respond more quickly to the onset of winter. They do this because the nights get longer.

Pure indicas and most hybrids therefore need at least ten hours of darkness to bloom. Some strains, by the way, are real night owls and need as much as 11 hours of darkness. So it depends very much on the genetics of the plant when your weed plant will flower.

Flowering time of the weed plant

The onset of flowering of a weed plant therefore depends partially on the genetics of the plant. Some weed plants need less darkness to be able to detect that it is time to flower. At the latitude of Amsterdam, it is dark enough at night around the end of August for most weed plants. Elsewhere in the world, the onset of flowering is on average later or earlier. This has to do with the seasons and therefore the length of the night. Further on in this article you will find a growth calendar where you can see the differences in day and night lengths in different places.

Weed is already blooming - Causes

First of all, it is by no means always a bad thing if your plants start flowering earlier in the season. A month earlier can in fact have its advantages. But we will tell you more about the advantages and disadvantages later. First a brief summary of the possible causes of early flowering weed plants.

Starting too early

The number one cause of early bloomers is starting to grow weed too early in the year. Especially if you start growing a photoperiod weed plant in April or even March, the plant will want to flower as soon as possible. In the Netherlands, northern Germany and a large part of the United Kingdom, the night is just as long as in September! Reason enough for a weed plant to think that winter is coming and that flowering increases the chances of survival for the offspring.

Avoid early flowering? Put weed plants outside when it is dark for a maximum of 10 hours a night. Preferably a little later in the spring. Further on you will find a handy chart for placing your weed outside. For the Netherlands, the rule of thumb is: after Ice Saints (11, 12 and 13 May) the plants can go outside.


We described earlier that it matters whether your weed plant has predominantly tropical sativa ancestry or comes from a more moderate indica bloodline. With hybrids it's a toss-up, but the chances are that if your plant has narrow leaves, it will flower sooner but also longer.

Light pollution, moonlight and light leakage

Growing weed outdoors in an urban environment has a downside. Those orange street lights contain exactly the same type of lamp that is used in grow tents! If your plant is too close to a lamppost, then from the moment it is outside, your weed plant already receives the signal that it is not really getting dark at night. The result? Your weed plant will not flower or experiences so much stress that it becomes ambivalent (hermaphrodite). But your weed plant will not flower sooner because of it. Street lighting that affects plants, animals and people is called light pollution.

Do you have a street lamp close to your garden? That can cause problems for the flowering of your weed plant.

Light leakage is a term that indoor growers may be familiar with. If your growing space is not hermetically sealed off from the outside world and cracks or gaps allow a little daylight in, you have the same problem. Then weed plants can get confused and fail to flower or shoot back into growth once they have flowered. Weed plants need to be in complete darkness at night. Even if you use alternative growing schedules, not a single speck of light is allowed in. There are, however, special green lamps that allow you to enter a growing space in the dark, but that is not the point of this article.

What about moonlight? Does that harm the weed plant? No. Moonlight is natural and even a full moon in clear skies does not reflect enough light (0.3 lux) to affect the start of flowering in your weed plant. To compare: adequate lighting on weed plants is in a range of 15.000 to 75.000 lux).

Relocation and/or given too little artificial light as a seedling

When you move a weed plant, it is very likely that the light is different from its previous location. Especially when you start pre-growing a weed plant indoors and have not quite got the hang of the light, your weed plant may tell itself that it is time to flower. When pre-growing, make sure that:

  1. The hours of light per 24 hours period should match the sunlight at the time of placing outside.
  2. The light on the young weed plants should be at least 5000 lux.

Pre-growing weed or pre-growth is very advisable, by the way. But don't do this on a windowsill without a grow light. Photoperiod weed plants in particular do not handle that well. They get long and thin and can start flowering much too early.

Not really in bloom: pre-flowering

Don't panic, though! It may well be that your weed plant will remain in the growth phase for a few more weeks. Every novice weed grower wonders what the start of the flowering phase actually looks like. When determining the gender of a weed plant you should see the so-called pre-flowering hairs. The flowering hairs or stigmas of a weed plant do not develop from one day to the other. The development of these flowering hairs does, however, mark the period in which your weed plant will actually start to flower in about four weeks' time. But first she will get a hefty growth spurt. Sativas can now grow twice as big!

An auto flower after all

The last reason for early flowering is that you might have an auto flower seed. There can be many reasons for this. Maybe you mixed up two seeds, didn't read carefully or received a seed from someone without knowing which one it is. This happens regularly. What happens less often is that one of them ended up accidentally in a new pack of weed seeds. The chance that there is an auto flower among them while you are sure that you have not ordered it, is very small. Still, mistakes are made where people work, but proving that it is an auto flower is impossible. Certainly not if you look at all the possible causes for (too) early flowering weed listed above.

Advantages and disadvantages of early flowering

We have already told you that early flowering weed is not necessarily a bad thing. In fact, many growers are looking for ways to avoid trouble during the last weeks of flowering. Some are looking for an early flowering strain, while others are deliberately forcing the bloom by putting weed plants in the dark


  • Complete the harvest before autumn, reducing the risk of mould or autumn storms.
  • Improve weed quality by flowering under bright summer sun.
  • Your weed will be ready sooner!

There is really only one disadvantage. If your weed flowers earlier than intended, your weed plant will be smaller than it could be. In other words, there is a reason for such a growth phase. From the grower's point of view the purpose of the growth phase is to be able to harvest as much weed as possible at the end. Do you skip the growth phase or shorten the growth phase by flowering earlier? Then the plant remains smaller and the yield is lower. On the other hand, your weed plant will be able to flower in better conditions, which may even out the yield.

Re-veg – Reintroducing the growth phase

This brings us to the next question. Can a weed plant also be put back into the flowering phase? You can indeed put the ladies back into the growth phase, but this has more disadvantages than advantages. Weed plants are annual plants. After flowering, it is normal for the plant to die. It will not come back in the next season.

Re-vegging is done in the hope of achieving a higher yield or to keep the mother plant alive after flowering. You can do this by giving as much light as is usual in the flowering phase again. Are you giving an already flowering plant less than 10 hours of darkness a day? Then your plant can get strange leaves and start growing again within two weeks.

The disadvantage is that if you do this outside, the season does come to an end at some point. Then there is less light, the air is often humid and there is a risk of mould. Moreover, re-vegging itself takes a lot of time. Two weeks for the return to growth and another two weeks for the transition to the second flowering period.

Re-vegging or regeneration can be done endlessly, but it is certainly not easy. This allows you to keep a mother plant alive to preserve valuable genetics. This can have advantages in making weed cuttings.

Growing calendar for growing weed outdoors

Everywhere in the world the ideal time for placing your weed plant outside is different. One of the factors is that the soil must be frost-free. Weed plants are not resistant to ice and snow. So it is recommended that you keep a close eye on the weather forecast in the spring. Besides the fact that temperature plays an important part, it is also recommended that you determine when your weed plants get enough light in a day. You can use the following chart as a guide. 


at least 14 hours of light from:

at least 15 hours of light from:

at least 9 hours of darkness from:

at least 10 hours of darkness from:

Edinburgh, Copenhagen

13 April

26 April

16 August

30 August

Groningen, Hamburg, Liverpool

15 April

30 April

11 August

27 August

Amsterdam, Berlin, Birmingham, Hanover, Warsaw

16 April

2 May

10 August

26 August

Maastricht, Brussels, Cologne

18 April

5 May

7 August

24 August

Nantes, Zurich, Budapest

22 April

15 May

30 July

19 August

Madrid, Naples

3 May

10 June

1 July

9 August

Sydney, Cape Town, Santiago

20 November



23 January

The first places in the chart are the most northern. If you were to grow weed in the south of France, Spain or Portugal, it would take quite a long time to get at least 15 hours of light each day. This is because the sun is much higher in the sky. This is exactly why you can put your weed plants outside a little earlier. After all, they get much more light in a day here, so plants can grow huge in these parts. Sydney, Cape Town and Santiago lie south of the equator where the seasons are reversed. "Early spring" there means in October.

The darkness of winter also comes earlier the closer you are to the equator. This means that weed plants can bloom earlier in southern areas (in the northern hemisphere).

Promoting flowering of the weed (putting it in the dark) 

Then we arrive at the question: can you make outdoor plants flower earlier? Yes you can. You can choose a strain that flowers early, or stimulate/force flowering by putting the plants in the dark. We wrote an extensive blog on this subject full of tips and tricks. Read it here

Selection of Notorious Early Flowering weed seeds

To finish, we would like to introduce you to some well-known early flowering plants. We have heard several times that these plants flower earlier in the year than you would initially expect. So you can harvest them earlier than other weed plants.

Private Label

Wedding CakeGorilla GlueJack Herer

Paradise Seeds

White BerrySweet PurpleMendocino Skunk

Dutch Passion

Purple #1BlueberryDurban Poison

Royal Queen Seeds

HulkberrySpeedy Chile (Fast Flowering)Critical Kush

Green House Seed Company

Himalaya GoldBig BangExodus Cheese

For this article, we received the cooperation of Dutch Passion, Paradise Seeds, Green House Seed Company and Royal Queen Seeds.