Tips for growing autoflowering cannabis plants

These days, autoflowering cannabis seeds are highly sought-after because they're easy to grow and allow the grower to obtain several harvests in less than 2-3 months.

This type of strains can be grown in small terraces or balconies, as they tend to produce small plants of no more than 1m in height, provided they are grown in pots. When cultivated on soil, autos can easily grow higher than 100cm, and produce more bountiful harvests than in pots.

Think Different photo by Jon Peta from C.C.
Think Different photo by Jon Peta from C.C.

But to get the best results from auto plants, you need to take into account several factors, in order to achieve a smooth running from the very beginning and to avoid any problems during the process.

Let's see how automatic cannabis should be grown to obtain optimal and generous harvests.

Main traits of autoflowering cannabis plants

First of all, you should bear in mind that these plants don’t respond to the standard photoperiod, which means they don't rely on the amount of sunlight they received during the day to start flowering.

Therefore, their vegetative period is limited to a few days, and the number of days can vary depending on the strain, but it's usually between 15 and 30. This is the timeframe needed by automatic plants to feel mature enough to start flowering. Cannabis needs a certain amount of time to grow and start producing flowers, as well as trichomes, in order to catch the male's pollen and be able to reproduce the species.

Think Different seedlings
Think Different seedlings

It's during this limited period of time that you have to be extremely careful, so the plant is safe and doesn't stop growing. Over-fertilization, overwatering, high humidity, lack of light or direct sunlight, the wrong substrate, strong winds, and lack of nutrients, are a few examples of factors that can reduce the size of your plants.

Why are autoflowering plants so small?

As we have seen, there are several reasons for these strains to remain small.

Seed germination and first repotting

This is an important step that many growers overlook, but it’s vital if you want to prevent any future problems.

You can germinate your seeds the usual way, with the paper towel method, jiffy pellets, etc. We prefer to do it between two wet paper towels and then use the jiffy pellets, as this allows for the first and only repotting that automatic plants need.

How to germinate cannabis seeds
How to germinate cannabis seeds

Once the seed germinates, the primary root penetrates the jiffy and emerges on the other end, and the stem stretches a little bit, you can repot the seedling into its final container. Avoid re-potting your autos more than once, unless you are going to keep the plant just for a few days in the first container.

Pot size for autoflowering plants

The size of the pot is very important, as the smaller the pot, the smaller the plant. The reason is easy to understand: the plant does not have enough room to expand its roots, which results in slow growth.

When using a small pot, the plant's root system will quickly fill out the container, and then will slow down its growth, since there won’t be more substrate to fill. Given the impossibility to continue expanding further at the same pace, the aerial part of the plant will be flatter and smaller. In order to obtain the maximum production from automatic plants, it's recommended to grow them directly in the soil for several reasons.

Think Different growing in soil
Think Different growing in soil

When the root reaches the bottom of the pot and can't find any more substrate, the plant stops growing. This is why it's important to use pots that are tall rather than wide, so the plant continues to develop during the 30 days of its vegetative period.

How to prevent automatic plants from growing small due to a lack of substrate

The best thing is using containers that are large enough for the auto strain to develop without halts or stagnation during the 15 to 30 days of their vegetative period.

These pots should be much taller than wide, so the roots can penetrate more deeply into the substrate and the plant can become bigger and more branchy. These containers are called 18L Automatic plant pots, or square pots, but we also recommend smart pots and Alchipots, which burn the tips of the roots creating more hairs for enhanced nutrient uptake. You should use pots of no less than 20L.

The growth rate increases as plants grow
The growth rate increases as plants grow

If you use smaller containers, even if they're made of fabric, you'll also get smaller plants. The main advantage of a fabric pot is that it allows for higher water evaporation, providing the substrate with longer wet and dry periods, which stimulate the roots and make them grow further.

Watering autoflowering plants

Another important factor you should take into account to ensure that everything runs smoothly and to avoid growth stagnation during the vegetative period.

Since you're only going to repot your seedling once, and the first container will also be the final one, the plant will always be at odds with the size of the pot.

When growing non-autoflowering strains, we use small containers in order to have better control of the irrigation, because, in the event of overwatering, the pot will dry quickly.

Think Different growing steadily
Think Different growing steadily

But, what happens to small plants in large containers? You can't water big pots with large amounts of water on the first day and wait for them to dry. If you overwater them, the substrate will be wet for many days, stopping the plant from growing, since it won't need to go in search of water during those 15 days.

How to water autoflowering plants

How should you water your automatic strains? With very little water, since the pots will be very large and the plants very small. 200-300ml per plant is enough for 18L pots, which means you can water them every 2 or 3 days without flooding them. On sunny days with high temperatures and low humidity, your plants might need more water, so you can double the amount, but try not to saturate the container.

Continue with this irrigation regime until your plant has grown a few inches, and then provide it with a higher amount of nutrient solution.

Think Different halfway its growing period
Think Different halfway its growing period

Once your auto has grown and you can tell it's about to flower, treat it like a regular plant. At this point in time, the root system will have spread almost in its entirety, and it will be able to absorb a bigger amount of water in less time than when it was smaller.

Autoflowering plants nutrition

How should you feed your automatic strains? This is also a recurring question between many new growers.

Feeding autoflowering plants can be tricky at first, especially if you still haven't mastered cannabis cultivation. You need to be careful not to overfeed your plant, as this can be counterproductive with this type of crop.

Think Different with the right amount of nutrients
Think Different with the right amount of nutrients

An excess of nutrients will cause the leaves to adopt a claw-like form, and the plant will stop growing due to salt accumulation. While it's true that many times the growth doesn't slow down too much, an excess of nitrogen can affect the flowering period.

We're back at the limited growth problem. After a month or so of growing, the plant will start flowering, and if you overfeed it at this moment, it won't have time to use the stored nutrients (nitrogen in this case), and will end up flowering with a nutrient imbalance in its metabolism.

Think Different with the same treatment but a lighter green colour
Think Different with the same treatment but a lighter green colour

This imbalance means that a plant with an excess of nitrogen will stretch further, increasing its internodal spacing and producing slender buds. The excess of N makes the flowers small and compact, which at a visual level can be seen as 4 buds scattered around the plant, instead of a single and large bud at the very tip of the plant.

Can you flush your cannabis plants to leach off the substrate? Yes, you can, but many times it'll be too late since the buds will have developed differently on a morphological level.

How to avoid nitrogen overfeeding

To avoid problems arising from excessive use of fertilizers, the best solution is to use a potting soil that only needs water and some or other root stimulator throughout the vegetative phase.

Think Different finishing stretching before flowering
Think Different finishing stretching before flowering

This type of soil, such as All Mix, is designed so the plants can keep growing during 4 weeks without anything else. After this period, you should use liquid fertilisers.

As we discussed before, your plant has 4 weeks to grow, so this soil is ideal to avoid any problems from the beginning, and once the plant starts blooming, you'll need to provide it with bloom fertilisers, as if it was a standard, photoperiod plant.

The best soil for automatic plants

Although many people overlook it, the substrate is the basis of the entire crop, which means that if you don't have the best substrate, everything becomes much more complicated.

A good sized Think Different
A good-sized Think Different

The ideal substrate for autos must be very fluffy, as their roots and growth are time-limited, and you should allow for a maximum expansion before they initiate the flowering period.

If instead of using an adequate substrate you use any other, your plant will have difficulties to conquer it, creating a very small root mass, which translates into a slow and stagnant growth with minimal nutrient uptake.

Using trichoderma is a great option to boost the plant's root system in order to make it stronger and more resilient and effective. It will also protect the roots from possible fungal infections, such as pythium, and will help the plant to have a better symbiosis between the substrate and the root, allowing for a greater ion-exchange which will highly increase the nutrient uptake, especially when using organic fertilisers.

Think Different at the end of its flowering period
Think Different at the end of its flowering period

A mix of white and black peat, perlite and coco is a good combination to create a quality substrate. We recommend mixing coco coir with soil to make it fluffier, and also to get lower water retention to facilitate the drainage and the drying of the substrate.

If the entire process runs smoothly and without any issues, you'll obtain high-quality buds, since modern automatic strains have improved a lot in terms of production, potency and flavour.

Think Different ready to harvest
Think Different ready to harvest

We hope this guide will help you to achieve an easier, more balanced, and problem-free crop, so you can enjoy marijuana of the highest quality.

We can't finish this article without thanking grower Jon Peta from C.C., who has kindly lent us his photos and is a great cultivator and a better person!

Thanks, Jon!


The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.

Comments in “Tips for growing autoflowering cannabis plants” (1)

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Merle 2020-10-30
I use coco perlite 70/30 and the seeds aren't auto just fem. What's the best nutrition for them. I've got led light and I use cloth pots. When I start them do I add nutrition? I used veg/tap and blue life and molasses. Is it too much? When watering I water until I runs down then after it starts running to my main drain I add veg, life every other watering and molasses every other week. In between nutrition water... Am I doing this right? Thank you... I know it's a lot of questions but I'm an old school grower and I have timers because I have the new LEDs that doesn't the bloom button.

Alchimia Staff

Tim Alchimia 2020-10-30
Hi Merle, thanks for your comment and questions. It sounds like you've got things pretty much under control there. It's difficult for me to give exact directions on plant nutrition without knowing the type of genetics you're growing and the power of the lamps you're growing under. As a general rule, the more light, the more fertiliser needs, and Indicas will accept higher levels of fertiliser than Sativa varieties, but there are plenty of exceptions to this rule. You can't really go wrong using a good quality basic cannabis nutrient line with one fertiliser high in Nitrogen for the growth period and another higher in Potassium and Phosphorous for the flowering stage, sometimes in combination with a bloom stimulator of some kind. Molasses are great to add to your irrigation schedule and work well for feeding the microbial life in the substrate but they don't offer much in the way of nutrition for the plants themselves. As for the watering itself, it's quite difficult to overwater when using fabric pots, so I think you'll be okay in that respect, but a moisture meter can be a great help in these situations. You can find more information on our blog, where we have at least one article about growing in coco fibre that should be useful. I hope that is helpful, please don't hesitate to ask if you have any more questions. Best wishes and happy growing!

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