What is the Lucas Formula?

As mentioned on the Growing Marijuana page, providing nutrients is a crucial element that you need to pay close attention to when you start growing marijuana. Your marijuana plants cannot thrive or produce high quality yields without a well-balanced nutrient regime.

Following the manufacture’s feeding schedule is a good way to provide your plants with the correct amount of nutrients. However, sometimes the instructions on the bottle can seem like a hassle or too complicated to follow. This is where the Lucas Formula comes in to simplify your feeding schedule.

The Lucas Formula is a feeding method for hydroponic and soil-less grows. It derives from a man named “Lucas” who participated in online growing forums. His feeding schedule quickly spread throughout internet communities as an easy and hassle-free way to feed your plants.

This formula takes General Hydroponics’ 3 part Flora series nutrients and simplifies it into only 2 parts. The standard Flora series includes Flora Gro, Flora Micro, and Flora Bloom. These 3 bottles are used in different ratios throughout all stages of growth.

With the Lucas Formula, only the Flora Micro and Flora Bloom are used. Lucas concluded that the Flora Micro provides enough nitrogen and minerals that the Flora Gro is not needed.

How it works

Throughout the entire grow (vegetative and flower cycle) you mix a ratio of 8ml of Flora Micro and 16 ml of Flora Bloom per US gallon of water. Again, this ratio of Flora Micro and Flora Bloom is used during ALL stages of growth.

It’s as simple as that!

Ok here is an example:

Say you have 1 plant growing in a container with soil-less medium and this plant needs 1 gallon of water every week. At the start of the week, mix 8ml of Flora Micro and 16 ml of Flora Bloom into that gallon of water.

Use that gallon of nutrient/water mixture throughout the week at your normal watering schedule. At the end of the week, you will have ran out of that gallon of nutrient/water mix.
Repeat the cycle for the next week by , again, mixing 8ml of Flora Micro and 16ml of Flora Bloom into a new gallon of water. This cycle is repeats itself over and over until you eventually harvest your crop.

What about hydroponic systems with reservoirs?

     

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So your hydroponic garden uses a reservoir like an Ebb and Flow, Aeroponics, or Deep Water Culture (DWC) system. Using the Lucas Formula is just as easy.

There are two methods for hydroponic systems with reservoirs. The Top-off method and the Add-back method.

Top-off Method:

For this method to work, you first need to figure out the water capacity of your reservoir. Fill the reservoir with water and mix in the nutrients at a ratio of 8ml Flora Micro and 16ml Flora Bloom per gallon of water in your reservoir. Adjust the water mix to the desired pH level.

Come back every day to top-off your reservoir to its original capacity with pH balanced water. No nutrients are added to the water when topping off the reservoir.

Keep track of how much water you are using to top-off the reservoir every day. When that amount of water equals the total capacity of the reservoir, it is time to clean and dump the reservoir. You then repeat the process by filling the reservoir with fresh water and nutrients.

Here’s an example:

Suppose my reservoir has a 10 gallon total capacity of water. I would start the week by mixing in 80ml of Flora Micro (8ml x 10 gallons) and 160ml of Flora Bloom (16ml x 10 gallons).

Now say my reservoir loses 1 gallon of water per day due to either plant usage or evaporation. I would then top-off the reservoir with clean (no nutrients) pH balanced water every day for 10 days.

On the 11th day, I would clean and dump out the reservoir and start over with fresh water and nutrient solution. This is because the topped off water has now equaled the initial 10 gallons of water (1 gallon x 10 days = 10 gallons of topped off water).

This cycle is repeated for the entire grow from early growth to final harvest.

Add-back Method:

With the Add-back method, you again fill your reservoir with water and the nutrient mixture of 8ml Flora Micro and 16ml Flora Bloom per gallon. Come back every day to top off the reservoir with the same full strength ratio of Flora Micro, Flora Bloom, and pH corrected water.

You continue to add-back 100% nutrient mixed water every day without ever dumping the reservoir. The only time you clean and dump the reservoir is when you switch between the vegetative cycle and flowering cycle.

Using the same 10 gallon reservoir as an example:

On the first day, I fill my reservoir with 10 gallons of water and 80ml of Flora Micro (8ml x 10 gallons) and 160ml of Flora Bloom (16ml x 10 gallons).

Again let’s assume that my reservoir loses 1 gallon of water every single day due to either plant usage or evaporation.

I would then come back every day to top off my reservoir with fresh water and 100% strength of nutrients. In this case, every single day I would fill my reservoir with 1 gallon of water, 8ml of Flora Micro, and 16ml of Flora Bloom.

This add-back of water and nutrients is completed every single day until it is time to flower the plants. At that point, I would dump the entire reservoir and re-fill it with 10 gallons of water, 80ml of Flora Micro, and 160ml of Flora Bloom.

Continue to fill the reservoir with 100% nutrient/water mixture until it is time to harvest your weed.

What is the preferred method?

There is no right or wrong answer here. However, I personally preferred the Top-off method. I like the idea of being able to clean the reservoir every so often and starting from a blank slate by remixing the water and nutrient solutions.

This gives me peace of mind that no buildup of contaminants are staying inside the reservoir. This also gives me a chance to start fresh in the event that I made a calculation error during the initial mixing of water and nutrient solution.

Again, there is no right or wrong answer here and it is always encouraged to try out every method or technique.

Let’s talk about water

The Lucas Formula was initially created for using Reverse Osmosis (RO) water. When mixing the correct ratio of Flora Micro and Flora Bloom with RO water, you almost always get perfectly balanced pH levels.

You can typically obtain RO water from your local grocery store but this can become inconvenient and somewhat suspicious. Many grower’s opt-in to invest in their own Reverse Osmosis water system.

Tap water can also be used with the Lucas Formula, however, more monitoring of water conditions will be required. You will absolutely need a pH meter and pH up/down solutions to correct the pH levels of tap water.

Overall Thoughts

The Lucas Formula is super easy to do with any hydroponic garden. This is personally my favorite feeding schedule to follow as it does not require a lot of time and effort on my part. It produces excellent results and is definitely a fan favorite among many growers.