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How Many Cannabis Plants Can You Grow Per Square Metre?

Congratulations on committing to cannabis cultivation. Now you need to settle upon the right number of cannabis plants to grow. We’ve got practical advice you can use to determine how many plants to fit per square metre.

Factors that determine how many plants you can grow per square metre.

  • 1. Factors that determine the number of cannabis plants you can grow
  • 2. Cannabis strain genetics
  • 3. The size of your indoor grow
  • 4. The size of your pots
  • 5. Training your plants
  • 5.a. Sea of green (SOG)
  • 5.b. Topping and fimming
  • 5.c. Mainlining and lollipopping
  • 5.d. Low-stress training (LST)
  • 5.e. Screen of green (ScrOG)
  • 6. The grow lights you use
  • 6.a. Guidelines for number of plants under HID lighting
  • 6.b. LED grow lights
  • 1. Factors that determine the number of cannabis plants you can grow
  • 2. Cannabis strain genetics
  • 3. The size of your indoor grow
  • 4. The size of your pots
  • 5. Training your plants
  • 5.a. Sea of green (SOG)
  • 5.b. Topping and fimming
  • 5.c. Mainlining and lollipopping
  • 5.d. Low-stress training (LST)
  • 5.e. Screen of green (ScrOG)
  • 6. The grow lights you use
  • 6.a. Guidelines for number of plants under HID lighting
  • 6.b. LED grow lights

Before you get started with your indoor grow operation, you need to have a plan. Among the things you need to think about is how many cannabis plants you can feasibly fit in your grow space.

FACTORS THAT DETERMINE THE NUMBER OF CANNABIS PLANTS YOU CAN GROW

From the available space in your tent to the size of your pots and the type of lights you’re using, several factors influence the number of plants you can reasonably fit per square metre.

CANNABIS STRAIN GENETICS

The first thing to consider is the type of cannabis you’re growing—the strain genetics. Sativas tend to grow tall, while indicas are stocky and bushier. Autoflowers grow particularly short, with some varieties reaching only 50–60cm.

Even those without significant spatial limitations tend to choose shorter cannabis varieties when growing indoors. After all, you are responsible for providing illumination, so you need to account for the space taken up by your grow lights. Moreover, if you’re growing different strains and some end up being much taller than others, this can deprive smaller specimens of light, resulting in stretching and reduced final yields.

If you don’t plan on training your plants, consider growing the same type of strain, or two strains with very similar heights, to avoid running into issues with spacing and lighting. Of course, the smaller and more compact your plants, the more you can fit per square metre. It’s up to you to decide if you’d rather crop several small autoflowers or just one or two ultra-vigorous hybrids.

THE SIZE OF YOUR INDOOR GROW

The dimensions of your growing area will largely dictate how many plants you can grow per square metre, and in general. If you’re like most home growers, you’ll likely be using a grow tent set up in a suitable location in your home.

Grow tents are available in many different sizes, from small 50 × 50cm tents to large ones that could fill half your room. The right size depends on what strain(s) you’re growing, how large your indoor growing space is, and what type of grow you are going for (heavy training, leaving plants to develop as is, etc.).

As an example, if you just want to grow a single untrained photoperiod indica plant, a 1 × 1m tent should be sufficient. As you add more plants, you’ll need to scale up accordingly. But again, don’t just account for the eventual size of the plants themselves, but also lighting, ventilation, and other equipment.

THE SIZE OF YOUR POTS

Depending on the diameter of your pots, several can fit into one square metre. But the size of your containers doesn’t just impact how many plants can fit per square metre, but also how big the plants will get overall. Said differently: The larger your pots, the bigger your plants will get.

Recommendations for pot sizes:

½ litre: Seedlings and young plants up to

15cm
2–3 litres: Plant height up to

25cm
5 litres: Plant height up to 60cm
11 litres and more: Average plant height (check strain description)

For the average indoor grow, you can fit nine 11-litre pots per square metre.

Use rectangular planting pots to fully take advantage of your available growing area. With round planting pots, you’ll be wasting valuable space.

See our planting pot calculator to find the optimal pot size for your cannabis plants.

  • 21L – 1 plants m²
  • 18L – 2 plants m²
  • 15L – 5 plants m²
  • 11L – 9 plants m²
  • 5L – 18 plants m²
  • 3L – 25 plants m²

The environmentally friendly RQS fabric pot, complete with proprietary “Aqua Breathe” geotextile layer, lets your plant’s roots breathe for optimal growth.

The environmentally friendly RQS fabric pot, complete with proprietary “Aqua Breathe” geotextile layer, lets your plant’s roots breathe for optimal growth.

TRAINING YOUR PLANTS

With plant training techniques, you can keep the number of cannabis plants to a minimum while maxing out their potential. Each of these training techniques is designed to optimise space and increase yields.

SEA OF GREEN (SOG)

4–16 plants per square metre
Outcomes: Fast yield, keeps plants short, easy to perform, comparatively smaller yields per plant

The sea of green method (SOG) is all about getting the most out of your available floor space. It is a good way to achieve a consistent outcome with photoperiod plants, clones, and autoflowers. This technique is fast and profit-yielding.

In a SOG, plants only get 1–2 weeks of vegetative growth before they are forced to switch to flowering. No pruning or training is needed. As the plants don’t have time to branch out, the result is many short plants with short main colas.

Under a 400W HPS light, you can fit 4–16 plants per m² in 5–12l containers. An optimal SOG grow can deliver multiple 500g/m² harvests per year.

TOPPING AND FIMMING

2 large/5–10 small plants per square metre
Outcomes: Simple to perform, keeps height in check, boosts yield, prolongs growth phase

Topping and fimming are high-stress training methods. By cutting off or pinching the main growing tip, you break the apical dominance of a plant so it develops multiple main colas instead of just one. This naturally results in bushier growth and causes plants to stop growing in their characteristic Christmas tree shape.

Any high-stress training technique that involves damaging your plants (like both topping and fimming) slows down growth and extends the vegetative phase. If you’re pruning, topping, and/or fimming, allow your plants to recover and expect a later harvest date. Don’t overdo it; top or FIM 2–3 times per growing season.

MAINLINING AND LOLLIPOPPING

1 large/2–4 small plants per square metre
Outcomes: Challenging to perform, consistent results, options for beginners and more advanced growers

Mainlining and lollipopping are two plant training techniques that promote the growth of large buds at the ends of branches.

Mainlining

Mainlining is a mix of topping, LST, lollipopping, and ScrOG. Plants are topped at the third node, with all the lower branches cut. This causes new growth to develop equally from one central hub, and plants are often topped a second or third time to develop multiple colas and an even canopy. This can fill up your grow space significantly depending on how many colas and the size of your pots, so keep in mind you may be able to fit fewer mainlined plants per square metre.

Lollipopping

Lollipopping is complementary but can be done on untrained plants too. All branches—including the main stem—are trimmed of unnecessary growth, leaving only the main bud and side branches with large buds. Just as with mainlining, the plant now directs energy toward the large buds.

LOW-STRESS TRAINING (LST)

2–4 large/4–6 medium plants per square metre
Outcomes: Suitable for autoflowers (no topping needed), best for beginners, requires no major recovery time

LST is a beginner-friendly training technique. You’re essentially just bending and tying down stems during vegetative growth to manipulate plants into growing horizontally. LST can be combined with other techniques, such as ScrOG. It is often done together with topping to break apical dominance, but it can also be performed without topping on autoflowers. Between 2–4 plants trained with LST can effectively fill 1m².

SCREEN OF GREEN (SCROG)

1–2 large plants/4 medium-sized plants per square metre
Outcomes: Best yield per square metre, flexible with how many plants you want to use, for advanced growers only

A ScrOG is the best way to utilise a single square metre of growing space. In this advanced training method, the screen is a grid-like mesh (chicken wire, netting, etc.) through which shoots of developing cannabis plants are woven to control growth. Growers usually start weaving their ScrOG during the vegetative phase and end it before the third week of bloom.

A ScrOG keeps only the main colas under the light so the plant’s energy goes toward bud production. Top your plants early to get more branches, then proceed to train them in multiple directions through the screen. This way, you can get the maximum yield from your available growing space.

You can choose how many plants/pots you use for a ScrOG. You could fill your space with only one monstrous plant in a large 20l pot, but you could also grow several smaller plants, such as four medium-sized plants each in a 10l pot.

THE GROW LIGHTS YOU USE

The last factor that determines how many plants you can fit into each square metre of your grow space is the type, and intensity, of your grow lights. This becomes ever-more clear when you realise that grow lights don’t spread light evenly across the entire area.

The greatest light intensity (and thus the fattest buds) is right underneath the light, then decreases significantly toward the sides. This could make growing fewer plants more sensible, as you’ll probably be sacrificing yield to poor light spread if you cram in too many. There’s no point in depriving any of your ladies.

If you’re growing weed with HID (high-intensity discharge) lights, a simple formula can give you a rough estimate for the recommended number of plants. Divide the wattage of your light by 75 and round up the fractions.

GUIDELINES FOR NUMBER OF PLANTS UNDER HID LIGHTING

  • 150W HID ÷ 75 = 2 plants
  • 250W HID ÷ 75 = 3.3 or 4 plants
  • 400W HID ÷ 75 = 5.3 or 6 plants
  • 600W HID ÷ 75 = 8 plants
  • 1000W HID ÷ 75 = 13.3 or 14 plants

When using CFLs, divide by 150. For example, using a 400W CFL: 400W ÷ 150 = 2.6 or 3 plants

LED GROW LIGHTS

Modern LEDs output the same power as HPS using only 60% of the energy. Therefore, they cover the same space in less wattage. A good 250W LED is equal to a 400W HPS, which can cover around 5–6 plants. By comparison, a high-powered 1200W LED should be able to cover around 8–9 plants.

However, keep in mind that wattage is only one value to consider when it comes to determining the power of your LEDs, as many other variables—including the type of LED—impact their effectiveness too.

When using LEDs, it is best to consult the manufacturer for the recommended number of plants to grow and the optimal distance from your lights to your plants’ canopy. Reputable manufacturers usually make this type of information available.

  • PRO TIP: If uncertain about how many plants you want to grow, it’s always better to keep it “safe” with fewer plants. Two large but happy plants with fat buds will ultimately be better than a tent full of small, light-starved cannabis that will only yield mini buds. In addition to that, you’ll also save on seeds.

Not sure how much marijuana to grow? This blog will help you figure out the right number of cannabis plants to fit in each square metre of your grow space.

Autoflowering Cannabis

Autoflowering cannabis plants can sometimes seem magical; they’re still relatively new but they’ve made their own home among enthusiastic growers thanks to their fast harvests and amazing results. When they first came around, people weren’t too convinced of their potential, but things have since changed. Modern autoflowering strains are nothing like the old ones thanks to amazing advances made in genetics and creating hybrids. To be honest, I’ve seen some beauties that I didn’t believe were autos at first.

Like anything though, they have both pros and cons. Let’s start with the cons;

  • To ensure they grow big, you’ll need to take special care of them.
  • You can’t control how long they veg for.
  • You can’t take clones from them.

Of course, then there are the pros;

  • They’re extremely fast plants, with as little as 55 days from germination to completion for some strains.
  • They can be grown both indoors and outdoors.
  • They don’t get stressed out by light contamination nor do they reveg, so there’s no need to worry about street lights interfering with their metabolism.

If you take care of autos properly then you can get amazing, decent sized plants that look nothing like those old autos that used to produce about 2 joints; these plants now produce top quality flavors, aromas and effects, and some would even say that there are strains that are better than simple feminized seasonal plants. You won’t be able to control the growth period, so if you plant them indoors, the first time you plant it should be a test; if you notice a plant growing too tall you can give it less water to stop the growth. If you’re growing in a grow tent, you should plant strains that take two months.

If you’re using a grow room then it doesn’t really matter whether the strain is 2 or 3 months, but make sure you don’t plant too many of them. If you have 2 month strains, 9 to 16 plants per square meter is enough, and if they’re 3 month strains then 4 to 9 is enough. The bad thing about these plants is that you won’t be able to clone any of them even if you wanted to, and growing has to be done through seeds every time.

So, in a couple of months your plants will be ready for harvest, rewarding you with a good yield and quality both indoors and outdoors. Autos are also the perfect way for many people to get around the pesky problem of street lights; they can cause plants on balconies to have issues with flowering due to having their dark cycle cut off, but autos aren’t influenced by light and they’ll flower perfectly under 24h of light; for indoor plants 20h of light is needed to get the most out of them.

There’s a huge amount of auto strains to choose from. There are bigger ones, smaller ones etc. depending on what other strains they’ve been crossed from. The fastest ones tend to come from a Critical or Skunk cross (AutoMass, Sweet Skunk…), whereas the bigger but slower ones tend to come from Jack Herer or Haze (Deimos, Magnum, Big Devil XL…). Now you can forget about waiting 4-5 months for your Haze, and plant a 3 month Magnum that has the exact same potency and taste, getting up to 100g.

Some of the Best Auto Strains:

Sweet Skunk Auto by Sweet Seeds

This strain takes two months indoors, with some long and thick buds right at the top of their branches. It’s extremely resinous and even the biggest leaves end up covered in perfect little trichomes and you can later use them to get amazing hash or BHO extracts. You’ll need to grow them in 7L pots, any bigger is unnecessary. These plants grow nicely, opening out their branches to allow the light to reach everywhere.

Due to how fast it grows, you’re going to need to be careful with how you water it at the beginning or you might end up with a dwarfed plant; I’ve managed to get 50g per plant with 9 plants under a 600w lamp. It has an earthy, sweet taste with a warm effect on your body that can even make you sweat, making for a nice relaxing sensation, especially after a long day at work. It looks ready to harvest around 45 days in, but trust us when we say that you need to wait those full two months if you want the best buds possible.

Deimos by Buddha Seeds:

These seeds take three months indoors even if it says from 60-70 days on the package; let them grow for 70-90 days under 20h of light, and don’t be in any rush to harvest them. These plants are gigantic, creating beautiful long colas of buds; they might not be the fattest buds but they’re extremely hard and compact. There are two phenotypes within this strain, one that begins flowering earlier and another that doesn’t seem like it’s going to flower at all.

The faster ones are ready in 70 days and can give you 80g in 7L pots, although you can plant this beauty in 11L pots if you want to. The slower ones begin flowering around day 40, and they’re the biggest ones with the record being held at 125g in a 7L flowerpot. Here’s a picture of it:

Deimos seeds have a rather long growth, so it’s hard to mess up so badly they end up dwarfed, and you should be able to get a nice 40-50 grams even if you’ve don’t something wrong. These plants like to eat a lot, and mine got to a 2.5 EC and had no issues, when I went to wash the roots out it went yellow from nutritional deficiencies and went entirely yellow by the time I harvested it 15 days later, but I got the most out of its flavor and potency.

It’s both incensed and earthy at the same time, having a hint of Jack Herer in it without a doubt; it’s neither overly relaxing nor too energizing, making it perfect for smoking during the day even when you have things to do.

Big Devil XL by Sweet Seeds:

Personally, this is one of my favorite tastes, with a nice and deep incensed taste that lingers. I planted a few and they were all pretty balanced in grow, same size and same yield ranging from 90g to 100g, although I got 30g from one that I deliberately overwatered at the start to see the difference between overwatered plants and properly watered plants. I have the dwarfed plant the same light and food, just more water, and even then it gave up 30g, making this strain a recommendable reliable auto strain.

The entire cycle takes around 90 days indoors under a 20h light period, and you’ll need to use preventive treatments for fungi as this strain doesn’t seem to have much of a resistance to fungi and you don’t want to risk an oidium infection. If you take care of this strain properly, place it in a nice sunny area and give it some soil that’s rich in nutrients, then all you’ll need to go is give it some bud fattening product towards the end of the second month. If you grow organically, make sure to make a nice mixture of guan in the substrate and use a fertilizer base like Bio Flores by Canna or Bio Bloom by BioBizz. Make sure you don’t harvest too early or you’ll lose quite a lot of yield, as that last month is really when the buds fatten up and get harder.

Here’s a couple of pictures of my indoor Big Devil XL’s, and an example of one that was over watered; if you over water at the start you’ll end up with a plant half the size of the one it could be, and I didn’t even over water this one that might. We got 30g from this plant, but severe overwatering on a 2 month plant will cause you to end up with 4 joints on one plant.

Magnum by Buddha Seeds:

This autoflowering plant is absolutely gigantic, and it’s perfect for growing outdoors in an extremely sunny area where you can get the absolute most out of it. Indoors, this strain can suffer a lot when it comes to heat because you’ll need to move the lights closer to them so it can reach the lower branches properly, and then it grows quite tall and only the tips of the branches develop correctly, so we don’t recommend this for indoor grows. It grows out nice long branches with buds all over. The buds are spongy and not too hard, meaning that it’s resistant to rot. It has an incensed taste and gives great quality buds in as far as weed and resin. They grow really tall, kind of like Christmas trees, and the branches are strong enough to put up with the weight of the buds.

This strain takes three months to completely finish its cycle, from germination to harvesting and you can get over 100g from just one properly taken care of plant. This strain also absorbs quite a lot of nutrients, so you can use quite a large dosage of flowering fertilizers, especially if you don’t want to end up with yellowing leaves all over your plants or a low yield. It’s also pretty hard to end up dwarfing this strain as it begins flowering around 40 days after you plant them and by then it will have grown enough to give a decent yield, making it perfect for beginners.

Now that you have a decent idea about which are the best (personal opinion) auto strains out there, you can get to planting them like any other plant. They’ll give you an amazing yield, an incredible flavor and aroma with which you’ll have plenty of good times with your friends or on your own. Submerge yourself in the world of autoflowering plants and you’ll learn how to get the most out of them. You can do various grows during the year outdoors and indoors, doing up to 6 grows a year in a grow tent. In grow tents you can germinate when your current plants have around 10-15 days to go, harvesting once every 45 days. Get ready to get some amazing yields from some amazing strains!

Author: Javier Chinesta
Translation: Ciara Murphy

Autoflowering cannabis strains; everything you need to know, including a list of our personal favorite autoflowering strains.