Feeding Cannabis Plants: What and How Much?

Let’s examine the age-old cultivators question… What to feed my plants, and how much? It’s a hard question to answer and you will get different information based on where you look and who you ask. If you ask the large nutrient manufacturers, they will point you at an expensive, multi-product line and suggest you feed your garden as much as you possibly can without killing your plants. If you ask an earth-mother type, they might suggest that messy, smelly organic teas and vegan composts are the route to go. Both of these examples can yield amazing cannabis but neither of them is a very scientific approach. A better way to figure out what we should feed our plants starts with examining the plants nutrient uptake profile and working backwards from there.

Nutrient Uptake Profile

Nutrient Profiling is a way of looking at a given nutrient product and identifying the products elemental makeup. N-P-K numbers are the most common way we compare nutrient products to each other, but a complete nutrient profile should cover more than just N-P-K – it should cover all the minor elements a plant needs to thrive.

Imagine that we have a nutrient solution and that we know exactly what the nutrient profile of that solution is. Now, let’s take that nutrient solution and run it in a hydro system for a period of time. If we take that solution and re-evaluate it’s nutrient profile after it has been used, we should be able to determine exactly what nutrients the plants used and how much they used –  this is how a plants ‘nutrient uptake profile’ is determined. This is powerful information… with this information we can mix a nutrient solution that has exactly what our plant needs in the exact right proportions without any waste.

Lucas Formula

The Lucas Formula is an approach to feeding your plants based on horticultural science and plant biology rather than nutrient company propaganda. It is a simple “Less is more” approach that will save you money on nutrients and give you great results.

Sometimes referred to as the ‘Lucas Ratio’, the Lucas Formula is a simple method for mixing nutrient solution in a ratio that is tailored to the cannabis plants nutrient uptake footprint. Basically, we know what the cannabis plants uptake profile looks like, and we can tailor mix a nutrient solution to match that profile. You can mix a ‘lucas formula’ from any nutrient brand, but in this article we will look at using General Hydroponics Flora line of nutes.

One of the first things you will notice when you look at the lucas formula applied to General Hydroponics Flora Line is that you don’t use any of the grow formula and that’s not a mistake. The Micro part of the 3 part GH line has all of the nitrogen a garden needs and, since the Lucas formula is a “less is more” strategy, you can skip using the grow part all together. You should change your reservoir once a week and top off the reservoir daily with pH adjusted water.

Vegatative mix:

Grow – 0ml per gallon
Micro – 5ml per gallon
Bloom – 10ml per gallon

Flowering mix:

Grow – 0ml per gallon
Micro – 8ml per gallon
Bloom – 16ml per gallon

The last week to 10 days of flowering should be used as a flushing period and all you will need to do is keep your reservoir filled with fresh, clean, pH adjusted water.

This feeding system works extremely well in hydro systems because the low ppm nutrient solution is unlikely to clog hydro lines. Also, since there is no organic element to this mix, it is a good opportunity to use hydrogen peroxide in your water. You can mix 15ml per gallon of 3% hydrogen peroxide into every gallon of water you put into your reservoir. The hydrogen peroxide will kill off any algae or fungus that can grow in a reservoir and it also releases oxygen in the root zone of your plants.

Great results can be achieved with this simple mix and all you need is 3 things… GH Micro, GH Bloom and hydrogen peroxide. You can feed a small hydro garden with 10 gallon reservoir for two cycles with about $35.00 in nutrients using this mixture – and you will find that the end result is nothing less than spectacular.

Check out our Cannabis Nutrient Uptake Profile chart and more info on mixing Lucas Formula Nutrient Solutions with products other than GH.

  1. How can you ever apply this to any other brand of nutrients? Or on soil? This will only work with General Hydroponics in a hydroponics system. What about lighting? That would also change a plants needs, right?

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