Explained: The Lucas Formula to Growing Marijuana


It uses consistent and simple 2:1 ratios that are easy to mix and remember - even for the avid gardener ;-).

growtechdec2013-lucasformula.jpgFeeding plants is one of the areas that has possibly the largest number of variables and one of the most challenging areas of expertise to master in gardening.  Not only are there many theories on what to give and when, but these opinions can change dramatically from strain to strain, method to method, room to room and person to person.  Add yet another layer called “a mind numbingly large number of different companies manufacturing agricultural nutrients, supplements, enhancers and the like” and it’s enough to make anyone’s head spin. 

In this week’s Grow Tech we will be reviewing a simple, cost effective and popular synthetic feeding method known as the Lucas Formula. When it comes to feeding schedules, I recommend starting with something, simple and effective. Learn it exactly as prescribed. After you feel you have a handle on what the default method looks like and how your system reacts, you can start making adjustments to suite your garden’s specific characteristics as well as your personal preference.  I know with the strains I run, I usually keep nitrogen higher through a later stage in bloom than most manufacturer's default feeding schedule prescribes.  I only was able to gain confidence in this method after doing several threshold experiments which made it easier to determine the best amount of nitrogen for that strain, in that garden in my opinion. 
growtechdec2013-lucasformula2.jpgLucas Formula uses only 2 of the 3 formulas in any high quality synthetic three part (grow, micro, bloom) formulas i.e. General Hydroponics, Cutting Edge Solutions, Humboldt Nutrients, Advanced Nutrients Jungle Juice etc. Lucas uses ONLY the micro and the bloom formulas in the specific ratios described below and DOES NOT use the grow formula (the green bottle) at all.
The other nice part about the Lucas formula is that it uses consistent and simple 2:1 ratios that are easy to mix and remember, even for the avid gardener ;-).  Lucas provides two formulas depending on if you are using florescent growing lamps or HID growing lamps.
Any time you are using florescent growing lamps (T5, T8 etc.) regardless of the stages of  growth you simply use 5 milliliters of the Micro formula (brown bottle) and 10 milliliters of the Bloom formula (red bottle) for every one gallon of water you are using in your system and reservoir.  For example if you have an ebb and flow table with a 20 gallon reservoir used to fill and drain the tray, you would use 100 ml of Micro formula (5 ml/gal x 20 gallons = 100 ml) and 200 ml of Bloom formula (10 ml/ gallon x 20 gallons = 200ml). 
Top off the reservoir daily using a pH corrected water (water you have pH adjusted to your preferred range, usually between 5.6-5.8 in hydro) as required to maintain a full reservoir level. After adding back an amount of water equal to the amount of your reservoir capacity you should change the reservoir and put in fresh solution.  For example in the same system when you have added in 20 gallons of water total in topping off your reservoir daily, it’s time to change the reservoir.
I recommend having a separate “top off” reservoir that you have the appropriate amount of pH adjusted water pre-measured (in our example’s case, 20 gallons).  When that reservoir is empty you know it’s time to change your system’s reservoir. 
Anytime you are using HID (metal halide, high pressure sodium etc.) growing lamps you simply change the numbers from 5 ml/gal and 10 ml/gal to 8 milliliters of the Micro formula (the brown bottle) and 16 milliliters of the Bloom formula (the red bottle) for every one gallon of water in your reservoir.  Using our flood and drain system example with a 20 gallon reservoir, your would use a total of 160 ml of micro (8 ml./gal x 20 gal = 160 ml) and 320 ml of bloom formula (16 ml./gal x 20 gal = 320 ml).
These days, many gardeners are employing the benefits of fluorescent lighting for the vegetative stage of growth, then switching to HID lighting for the bloom stage.  Lucas recommends switching the ratios from 5 and 10 ml/gal to 8 and 16 ml/gal at the transition of the lighting your plants are getting. 

As always if you have questions or recommendations for topics please e-mail and HAPPY GARDENING!!!

We thought you might also like..

from the gallery