Hello Professor Lee

I have a question about PPM and EC. What is the difference between the two and is one better than the other?

Some Guy

Hello Guy

Good question. This one gives a lot of people problems. PPM stands for parts per million and EC stands for electrical conductivity. They are both methods for considering how strong a nutrient mixture is, but they just go about it in different ways. It’s kind of like the difference between using the metric or standard systems of measurement to determine how far you’ve traveled or how much sugar to use in a cake recipe. I always liked to use the PPM system simply because that was the style of the first meter I ever bought. Such meters are generally called TDS meters. TDS stands for Total Dissolved Solids. In my imagination I like to visualize a room filled with a million golf balls, and if my meter told me my PPM was 650 then I would imagine that 650 of the golf balls in the room were a different color than all the rest. I know it’s kind of stupid, but that’s the way I got used to thinking of my nutrient concentrations and it’s stuck with me ever since.

I find that most growers pick one method and from then on they’re a PPM or EC grower. It’s silly but true. Now that I’ve said that I should also point out that TDS meters are really variations of EC meters. At this point you should be thinking, “What the fuck?” Yep, that’s right. TDS meters use electrical conductivity to initially measure the dissolved nutrients and then convert that information into PPM. I think this is one of the major sources of confusion when discussing the difference between PPM and EC.  

As a baseline, pure water doesn’t conduct electricity, but the more mineral ions that are added, the higher its conductivity. This is the reason sea water conducts electricity more efficiently than fresh water.  Most PPM and EC meters pass a small electrical charge between two electrodes to measure this conductivity and give a fairly accurate account of the nutrient mixtures strength. When you mix up a batch of nutrients, be sure to check the water before you add anything to it. Any initial impurities in the water will show up in your measurement. For instance, my tap water measures about 100 PPM. If I didn’t know that beforehand I might think my mixture had more nutrients in it than I thought. 

I hope this helps,

Professor Lee

Hey Professor

I’ve got a mutant plant! It alternates between having only one leaf and branching site on one internode and then three leaves and branches on the next. All the other plants in my garden are normal and have the standard two leaves and branching sites per internode. Have you ever heard of this happing before? Will it keep doing it or correct itself in time? It’s about two months old and I’m growing it in a flood and drain hydroponic system under a 1000 watt MH lamp. 




Hello Matt

You’ve found yourself a plant that has a trifoliate growth pattern. I’ve only seen this in person a couple of times, as it’s kind of rare, but it does happen. Nothing is wrong with the plant, it just has a different growth profile than the rest of your plants. It should keep growing like this for the rest of its growth cycle. Sometimes the main stem of a trifoliate plant will spontaneously split and develop into two main stems. My suggestion is to enjoy the novelty of it. 

Good find!

Professor Lee

Hello Professor Lee

I like to grow in a 4x4 grow tent with CO2 and a 600 watt HPS. I grow my plants in a soil mix that I like to prepare myself. This time around I’ve tried a plain mix of coco, perlite, vermiculite, potting soil and a complete organic nutrient mix. They guy at the store told me that since it was calcium based I didn’t need to add any Cal Mag. Does that sound right to you? 

A. Grower


Hey A

Congrats on your state’s legalization! It’s one more excuse for me to head out to the Pacific Northwest again. Calcium is the building block for cellular division for growth within a plant this is one of the reasons that companies are starting to incorporate it in their products. If the nutrient mix you bought is calcium based then you shouldn’t have to add any Cal Mag, but I would suggest adding enzymes, such as Multi Zen, Zyme or Bio-Cozyme to the soil to help accelerate the mineral breakdown of the nutrients. The reason I suggest the enzymes is that you are growing in a sealed environment with extra CO2 and your plant’s accelerated growth will have heavier than normal nutrient requirements. 

I hope this answers your question and happy growing.

Professor Lee 

Hello Professor

I’m pretty new to growing and I’ve kept things simple by just growing a couple of plants in some five gallon buckets on my back porch. Last year’s crop came in at just under a pound dry and my friends liked it a lot! They claimed that it was really good and they weren’t just saying that to seem grateful for the free weed! The only complaint I got was from one friend who said that the ashes in his bowl told him I hadn’t flushed out the chemical nutrients I was using. I hadn’t told him what I used, but he was right about me not using any organics. This year I decided to try organics to see if he would say the same thing or not. So I’ve been buying compost tea from the grow store in my town that makes it there on site in this big tank. It’s pretty cheap and I don’t think I’m ready to start mixing or making my own organic stuff yet. Anyway there is a big sign next to the tank that says the tea is super charged with worm castings. I know that means worm poop and after it rains around here my yard is full of little piles of it. The next time I grow should I add some of these to my soil mix or would that introduce any bad microbes to my soil? Is such a thing worthwhile or should I just keep buying the compost tea? 

Thank you,


Hey Angie

Compost tea with worm castings is a excellent fertilizer to add to your plants and it’s important to support a local business. Until you feel comfortable mixing up soils and/or nutrients on your own it’s a great way to go. As for the worm casting you find in your yard, there is nothing wrong with adding them to your soil mix. They won’t contain any harmful pathogens like E.coli or salmonella; in fact quite the opposite! Fresh worm casting are full of beneficial bacteria that will help the plants access nutrients in the soil. I like to gather them out of my own yard and added them to my compost tea to give it a bit of a super charge. No matter what fertilizer source you use, be sure to flush the excess nutrients out of your soil with plain pH-balanced water starting about ten days before your harvest. This will remove excess nutrients from the plants and improve the taste and smoke of your buds. If your friend really knows their stuff they should be able to tell the difference. 

Great question and keep up the good work.

Professor Lee 

Hello Professor Lee

I am thinking of building my own hydroponic system myself. I am pretty handy with building things from wood or PVC plumbing pipes. I’ve been prowling the aisles of my local do it yourself and grow stores for parts and ideas. I’ve have a simple NFT system in mind but I want it to have sprayers instead of just a shallow flow of water on the bottom. I found some misters and wanted your opinion on the micron I should pick. Any suggestions? 


Oakland California

Hello Lincoln

How are things in Oaksterdam? When it comes to microns it all depends on how fine you want your spray. One hundred to two hundred microns will create a soaking spray like the one used in most commercially produced cloning boxes. Thirty to one hundred microns will produce a wet mist, and at zero to thirty microns you will get something akin to a dry fog that works great in an aeroponic system or even for foliar feeding nutrients to the plants. The finer the mist, the finer the root mass that can be generated. Higher micron sprays like the one to two hundred range have a tendency to blast the smaller fan roots off of the root ball and promote spaghetti roots. By dialing down the impact, the root ball can develop more of its hair thin side shoots and as the saying goes, “more root, more fruit”! If it was up to me, I would pick the smallest micron sized sprayer or atomizer I could get my hands on. Some models are adjustable, allowing you to play around with the settings and dial things in to whatever you consider the sweet spot for your particular setup. 

Good luck,

Professor Lee 

Hello everybody!

Thanks for sending your questions in, and please keep them coming. Angie’s question about worm casting really took me back to the start of my growing career and to help her out I sent her an autographed copy of my book Marijuana 101: Professor Lee’s Introduction to Growing Grade A Bud.  Keep sending your questions and next time it could be you that gets a book. 

Till then, happy growing.

Professor Lee

This article first appeared in Issue 118 of Weed World Magazine