How Long Does it Take for a Cannabis Plant to Grow?

Spoiler: it depends. But here we tell you what it depends on, how to calculate the timings and what you can do to make your plant grow healthy and at a good pace. 

Cannabis plants can take from 8-24 weeks to be ready for harvest. The time difference depends on several key factors such as genetics, environment or growing technique. 

This process requires patience and attention to each of its stages. From germination to harvest, each phase is crucial to obtaining a quality product. Each of the different stages of growing cannabis plants requires different conditions and techniques; a certain amount of water, light, nutrients, etc. 

Below, we break down the factors that influence the growth times of cannabis plants and each of the 4 stages of the cannabis life cycle, providing estimated timings and practical tips for you as a grower. This way you'll learn to tell when to use, for example, a growth fertiliser or when a flowering fertiliser for cannabis. 

You'll also learn basic concepts and some more complex ones to improve your growing and maintain perfect control of the different phases of your favourite plants. 

Factors that influence growth times

Genetics (Indica, Sativa or Hybrid) 

• Indicas: are faster varieties, flowering in around 7-9 weeks. 
• Sativas: are slower varieties, their flowering can stretch to 12-14 weeks. 
• Hybrids: intermediate timings, depending on genetic dominance indica or sativa. 

Seed type 

• Photoperiod seeds: with this type of seeds you decide when they flower. Their total cycle can go from 3 to 6 months, depending on how long you decide to keep them in growth. 
• Autoflowering seeds: These varieties grow and flower on their own. Normally they can be ready in 8-10 weeks from germination. Definitely the fastest, ready in about two months. Ideal for beginners or for express growing. 

Growing environment: Indoor vs Outdoor 

• Indoor feminised seeds: In this environment you can control the light, humidity and temperature, so the plant's life cycle is usually faster and more predictable. You set the pace, you can grow photoperiod crops with just 3 or 4 weeks of vegetative growth or grow autos in a continuous cycle all year round. 
• Outdoor feminised seeds: In this environment we cannot forget that you are at the mercy of the climate and season. The cycle is annual, you germinate in spring and harvest in autumn. Growth depends on the sun and external conditions that your plants are in, so this cycle can be slower and uncontrolled, but also more natural and economical. 

The 4 growth phases of a cannabis plant: Duration and care

1. Germination phase
2. Seedling phase
3. Vegetative phase
4. Flowering phase

1. Germination phase: How long does it take for a cannabis plant to germinate? (1-7 days) 

Germination is the first step in cannabis growing. It consists of activating the seed so the primary root sprouts. 

During this phase germination and planting of cannabis seeds takes place. The process that seems quick and simple actually has many small details, such as the appearance of that first root that begins to extend until it breaks through the seed wall and makes its way to develop and start absorbing nutrients from our substrate. 

In addition, the cotyledons will appear, that is, the first leaves of our plant, something that certainly excites us and shows us how our project is going swimmingly. The cotyledons are two small leaves that crown a first stem. By showing these two first initial leaves, we consider the cannabis plant to be dicotyledonous, a class of angiosperm plants whose embryos have two cotyledons and to which a large number of trees belong. 

To start the germination process we need to hydrate the seed. The ideal is to moisten it well for 12-24 hours. You can use gauze, damp napkins, jiffy pellets or specific germinators for this process. The ideal is to keep them in a dark place during this process and once the root appears, transfer it to the pot or soil you have prepared. Of course you can also germinate it in the substrate you have chosen directly, but you will have better chances of success if you germinate it as we tell you at Growlobby and then transfer it. With your finger you can make a hole of between 1 and 2 cm in your substrate and place the seed with its root downwards and the seed shell part upwards, covered with a little soil. 

Don't forget to maintain a constant temperature of between 20°C and 25°C and high humidity around 70%-80%. 

If there were problems during this phase, you can also use rooting hormones, a simple product that works very well and helps with root system stimulation of the plant. 

Once your seed germinates, it is ready to move to a growing pot or to your growing soil space, they can now be exposed to light and be watered once its primary root has sprouted. 

• Duration: 1 to 7 days. 
• Optimal conditions: Temperature between 20–25 °C and high humidity (70–80%). 
• Common methods: Use of damp napkins, jiffy pellets or specific germinators.

2. Seedling phase: How long does a cannabis seedling take to grow? (2-4 weeks)

Once the seed has germinated, the seedling emerges with its first roots and leaves. During this phase, the plant develops its root system and begins to strengthen its structure. 

It's time to transplant the seed, either to a pot where it has enough space to continue developing, or to the space you have prepared or planned for growing your plants. The root system will start to gain strength during this period, which as we anticipated earlier, spans between 2 and 4 weeks. You must be careful and provide the plants with a temperature close to 25°C and a relative humidity of around 70%. 

The leaves multiply in this phase and the plant begins to take shape and gain some height. 

You must be careful not to water the plant too much during this phase, as it has very small roots still and does not need an excessive amount of nutrients. Also, you should keep the environment clean to avoid diseases and the appearance of harmful fungi or bacteria at a time when your crop is still very fragile. 

• Duration: 2 to 4 weeks. 
• Optimal conditions: Soft light, constant temperature close to 25°C and moderate watering, trying to maintain a relative humidity of around 70%. 
• Care: Avoid overwatering and provide aerated substrate.

3. Vegetative phase: The rapid growth of cannabis plants (2-10 weeks, most commonly 4-8 weeks) 

This period covers a large part of the life of our cannabis plant. Here the plant focuses on growing: it develops stems, leaves, branches and roots. 

The duration of this period can vary depending on the type of growing we do, from just autoflowering seeds that can spend only 2 weeks in vegetative, to some super sativas that can reach 12 weeks of growth if you germinate them in March.

• In indoor growing they will need between 16 and 18 hours of light daily during a period that can vary depending on the growing technique you use. 
• In outdoor growing they will need at least 4-6 hours of direct sunlight during a minimum of one month, although timings can vary depending on the desired final size of the plant and the germination season. 

During this stage the roots develop exponentially strengthening the structure and root system of the plant. The foliage also increases and you should increase watering, something that is very relevant, as the plant is increasingly larger and the roots are more spread out, so its water demand begins to be much greater.

Also during this stage you can apply pruning of lower branches or start techniques like SCROG to improve structure and production. Take the opportunity for pruning, transplanting and training techniques (LST, topping). 

You can also use microorganisms for plants to improve the root system of your growing. 

• Duration: 2 to 10 weeks, what does it depend on? 

Autoflowering plants move to flowering after 2-4 weeks. 

Indoor photoperiod plants, the most common is that they are in vegetative phase between 3-6 weeks, there are varieties or growing styles such as sativas and scrogs that can extend this period between 7-10 weeks. 

Outdoor photoperiod plants, if you germinate in March or April, can be 8-12 weeks in the growth phase, until the days shorten in summer. 

• Photoperiod: 18 h light / 6 h darkness.
• Ideal temperature: 22–28 °C 
• Nutrients: High nitrogen (N) content 

4. Flowering phase: When does it start and how long does it take for a cannabis plant to flower? (8-10 weeks, but can extend to 15-16 weeks)

This is the final stage of plant development, In this period, the plant begins to form its first buds. This is the most anticipated and critical stage. 

The amount of light the plant receives is reduced to 12 hours if we have our indoor crops. If our crops are outdoors, from early July the nights start to get longer and our outdoor plants start to flower, that's when the resinous buds will start to excite you. This period lasts between 8 and 10 weeks, but can extend to 15 or 16 in some varieties, especially those known as sativas. 

This phase is probably the most anticipated by everyone, as the process comes to an end and your cannabis will be ready in "a short time". We can use bulking fertilisers to improve the size of these and obtain giant-sized buds. As the flowering stage progresses, the trichomes increase and the plant becomes more and more resinous. You should remember the importance of trichome colour, as it shows us when we should start to harvest. 

• Duration: 6 to 12 weeks 
• Photoperiod: 12 h light / 12 h darkness 
• Ideal temperature: 20–26 °C 
• Nutrients: Rich in phosphorus (P) and potassium (K) 

Check the pistils and trichomes from week 5 of flowering onwards to find out if your harvest is ready. 

If you want to know more about any other factor or have any questions about cannabis plants, don't hesitate to consult our website or ask our super experts, we help you so your growing doesn't fail!