How to Grow Giant Plants Indoors

By Erik Biksa
Published: July 1, 2013 | Last updated: August 5, 2022 07:15:59
Key Takeaways

Way, way back in the prehistoric days of living giants, plants were huge. Today, Erik Biksa offers tips on how you can bring that gargantuan scale back to life in your own indoor garden.

There is something to be said for a giant specimen of your favorite plant variety or strain. When the fan leaves make you feel small and you can literally take shade beneath your cultivated plant, you will know the feeling.


A single plant might occupy over 5 by 5 ft. of space at harvest time! While that is indeed a swell feeling, most of us as growers will get even more exited at harvest time: very large yields and exceptionally high crop quality are common characteristics of large grown plants done right. This article is aimed at giving you the foundation that you need to do it.

Good yields and excellent crop quality are only some of the advantages of growing very large plants. One of the other big benefits is that growers are able to maintain lower plant counts while achieving comparable yields to more conventional planting densities.


Experienced growers know that large well-developed plants are hardier; they withstand stresses that can happen during the cropping cycle much better and still yield well, whereas other less-developed plants will suffer greatly, resulting in significant yield loss. Just like in natural settings…

Some of you reading this might be saying, “Well, I don’t want to spend all that time growing my plants out in veg before I can flower them to achieve these large yielding sizes.” Fair enough; if you did everything the same as before and just spent longer in your attempt to create a monster, you might be correct. However, when we grow monsters, we need to create the right kind of environment for our plants to show their gargantuan freakiness for us. Everything has to be bigger! If you follow the prescribed methods, the few small healthy plants you transplant into huge containers with multiple light sources (which, I admit, looks inefficient) will quickly explode and fill up that large amount of space by harvest time.

The Keys to Growing Record-Breaking Sized Plants

It is hard to say with certainty what the world was like in the time of the dinosaurs, but it seems likely that plants would have had to grow fast and large to feed those gigantic creatures. It is surmised that elevated carbon dioxide (CO2) levels and a lot of healthy bioactivity in the soil (remember, there was no pollution back then) would have created the ideal growing environment—assuming that plants behaved the same back then as they do today. Genetics would have been relatively pure at that time; although, cross-breeds would have likely occurred as pollen or seeds naturally traveled considerable distances. Still, the cross-breeding would have been nothing like what humans have done to them.


Another factor that’s very difficult for us to guess on is light intensity and, possibly, spectrum (that is, we don’t know what the levels of those factors were during prehistoric times). It’s likely that light levels would have needed to be strong in order to support large and fast-growing plants that could feed herds of creatures that individually weigh more than several buses combined. So, we can surmise that gigantic plants need to be drenched in light from top to bottom.

And lastly, space; for plants to get monstrous, they will need the room to do it (this includes the necessary clearance for light fixtures and lamps).


So, in short, the components to the recipe for gargantuan plants that look like they came out of the Jurassic period are:

  • Elevated CO2
  • A very healthy and unlimited root environment
  • Genetics that are optimal for a given growing condition and that can cause a plant to be big
  • Huge amounts of light that hit the plant top to bottom
  • A lot of space

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Prehistoric Fuel for Plant Growth

The prerequisite for being an organic creature is to contain carbon. Interestingly, substances that growers add to their crop feeding programs, such as humic acids, are actually sources of carbon for our plants and their favored microbiology. Leonardite, the source of many humic acid products, is created from highly decomposed and fossilized ancient organic matter—potentially dinosaur guano!

Anyway, that entertaining fact about carbon aside, your plants will be able to gather more carbon (a very important building block in the growing process) from the atmosphere that surrounds the leaves via absorption of CO2 through the stomata, the tiny opening in plant leaves for exchange of gases.

Our present ambient atmospheric levels range from 400 to 600 ppm of CO2. These levels can get quite a bit higher (up to 1,200 ppm or higher) in unventilated work spaces with a high level of human occupancy. These amped-up levels are actually better for your gigantic crops. Your crop will grow much faster and larger when supplied with higher than normal ambient levels of CO2, and these very large and fast-growing plants will sense limitation if higher levels are not maintained. As long as the roots will not overheat or get stifled of oxygen (O2 levels are diminished in warmer temperatures), you can run the growing environment a few degrees warmer with increased levels of CO2. The increased metabolic rate can be supported with higher CO2 levels, especially when factors like light, nutrients and water are also increased or adjusted. This helps to promote faster growth rates and larger yields.

Ancient Grounds

A healthy root environment is highly active. In prehistoric times, consider that the soil would be free from growth-limiting contaminants and would have very specific and native species of microbiology and parent materials for feeding the plants that specifically developed in that growing region. This soil presented the “perfect storm” for crop feeding.

Today, it’s possible to develop your own microbiology and nutrient levels/diversity by creating your own mixes with raw materials or through more refined sources like prepared organic nutrient fertilizers and supplements. Also, by using pure water either from RO-filtered sources or from condensation recaptured from dehumidifiers and air conditioners, you can help encourage healthy microbial activity that improves plant hardiness and growth rates. Tap water, on the other hand, is commonly laden with chlorine and chloramines—substances intended to kill the types of microbes that you are trying to cultivate in the root environment.

Including a supply of humates and growth-promoting substances like kelp (or kelp extracts) helps to fuel your plants. They provide a higher rate of metabolism at the roots, propelling upper portions of the plant to grow faster and ultimately yield larger. The substances that are found in these and other sources of organic materials can make your existing crop feeding program work better too in the majority of soilless gardens.

Gargantuan plants are going to need to be supported by bigger root systems. In some hydroponic systems root space is virtually unlimited. In bare-rooted hydro, just stick with a good synthetic program with tons of oxygen and you are set. In soilless or soil-based gardens, especially indoors, you are going to want to go as big as you can with your container or grow bag.

Just watch you don’t run out of vertical space between your increased container size, the clearance you need for your light and how big the plants are going to get. Raised beds are a great way to get more root space without adding vertical height, although you won’t be able to rotate your plants (unless you do mini-beds on castors).

Also, don’t overlook the importance of oxygen levels in your soilless growing mediums either (hint: micro-pore space nets you more O2 than macro-pore space in the same container volume).

Genetics That Snarl

If your plants don’t want to be big, you aren’t going to get the big bang for your buck like you might with another varietal choice. Some plants are just better suited to SOG (Sea of Green) applications because they don’t want to branch out or grow very big; it’s part of their natural tendency. Also, for the best results, look for plants that do a lot of growing once the light cycle has changed from a vegetative to flowering lighting regimen. This way, you aren’t spending gobs of money on power with longer daylight levels when you are running your grow lights 18/6 or 24/7.

There are some awesome cross-breeds out there for you to choose from. In fact, hybridization from diverse selection is the key to winning genetics; especially in this application. It is possible to combine the harvest characteristics of the stout shorter growers with the crazy growth habits of plants that are typically known to yield less dense flowers or fruits. So, if you are willing to grow out a seed crop and select for a mother for this project—look out! Using the types of genetics described here, a plant vegged to 18 to 24 in. can easily finish as a 5-ft. bush that can stand up to anything! Plus, it will have solid fruits or flowers from tip to container, and the crop quality will be awesome the whole way around.

Circling Back to Light

For things to really kick-off, you are going to need to do something slightly counterintuitive: put a lot of lighting over a smaller plant. Admittedly, it looks rather awkward to see a single plant less than 2-ft. tall with a 1,000-W HPS vertically overhead and with a vertical 600-W positioned beside it, but fear not! If you selected your genetics appropriately, within two weeks you won’t see the floor or walls easily anymore. The space will be quickly filled with very healthy, thick-stemmed and large-leaved branches that stack up swollen flowering sites one right after the other.

Just watch that with all of this increased artificial light you don’t cook the root system. Hint: vertical lamps allow you to light the plant canopy from the side, with little or no strong light radiating onto pots or grow bags. Also, to save on power, you can relay which lights come on and off during the lighting cycle; essentially, this is a system for moving light while lamps remain stationary. Hydro growers can add chillers to their reservoirs if conditions in the reservoir or root zone begin to heat past optimal levels.

Space—You’re Gonna Need It

If you haven’t given this method a go before and you create the types of conditions described above, you are going to be blown away by how such a tiny plant can fill so much space and quickly lead to such giant yields. However, this will only happen if you provide it with lots of space.

It might take a crop cycle to get your planting density relative to your set-up and variety type perfected, but the bottom line is that you won’t need nearly as much time in veg as you think. The first week or two will simply just look inefficient compared to what you are used to seeing; after that, it is confident to say that you will be a believer.

So, there you have it, take the leap of faith and give this prehistoric growing method a try for results you can club your friends over the head with.


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Written by Erik Biksa

Profile Picture of Erik Biksa
Erik Biksa holds a diploma in agriculture with majors in fertilizer sciences and crop production. Erik has amassed over 18 years of indoor gardening experience and intensive research. Since first appearing in Maximum Yield in 1999, the “Ask Erik” column and numerous articles have reached growers throughout the world.

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