by Nebula Haze
I love almost every aspect of growing cannabis, but my least favorite part is testing the pH of runoff water (to prevent deficiencies). Enter hydroponics. In a “DWC” (deep water culture) hydro tub like this one, pH is the easiest part of growing. You just dip a PH Pen in the water, and you’re done.
Growing cannabis in hydro is surprisingly easy when you start plants right.
Yet it’s the results of growing cannabis in hydroponics that makes you feel like a “mad scientist”. This outrageous Purple Ghost Candy plant approached a pound by itself.
My favorite part of growing weed in a big hydro tub is how little time and work it takes from day to day. In some ways, it takes even less work than “just add water” soil because you don’t need to water plants every few days, and testing the pH is faster and easier.
A quick peek “under the hood” of a DWC hydroponic reservoir. Look at those roots!
Learn how to grow cannabis in a hydro tub like this (step-by-step tutorial).
For those who are already growing hydro (or want to start), here are some insider secrets from an experienced hydroponic cannabis grower. These tips prevent common problems in hydro, while saving you significant time and effort.
7 Secrets to Healthy Cannabis Plants in a DWC Hydro Tub
If you’re thinking about growing cannabis in hydro, or perhaps you already have, this section will make all the difference for you. Simply follow these suggestions and you’ll avoid 99% of the issues cannabis hydroponic growers run into.
- Leave the roots alone – Don’t touch the roots, especially when they’re babies and the roots still look “feathery” and fragile. If you touch them or pick up the lid and move them around, they can easily twist up, which kills the roots below the twist point. When the roots look thick and sturdy, they’re way less sensitive and won’t twist anymore.
- Don’t change the water for first 30 days, or at least not until plants have solid looking roots. Pumping out and replacing all the water (or otherwise disturbing the roots) is one of the most common triggers of root rot (dying roots), especially with plants under 30 days old. At first, just top off with new water to maintain the proper water level.
- Use a root supplement – I personally use Hydroguard. This adds “good” microorganisms to the water that not only protect roots from pathogens or root rot, but also just helps them be more healthy overall. Hydro growers without a root supplement are way more likely to run into issues with unhealthy roots.
- Don’t let light beam onto the tub or get into the reservoir. Both the light and the heat cause things to grow. If you see anything green growing in the reservoir, chances are light is getting in. Cool, totally dark hydroponic reservoirs are the best performing reservoirs.
- Don’t let roots live in heat. The plant itself can be as hot as any plant, but without the protection of soil, if you heat up the water the roots get hot, and plants don’t like hot roots. If you happen to be an outdoor grower in the sun, if you have potted cannabis plants, put them into an even bigger pot. The extra layer of air between the roots and the sun’s beams makes plants much much more resistant to heat and overall stress.
- Keep an air gap (don’t fill the reservoir too high) – Make sure there is an air gap under the net pot. This greatly increases root health. The air bubbles will be bursting, so that the roots are constantly getting a mist of water. But if you fill the reservoir so that it’s actually touching the net pots, it causes roots to get unhealthy, and then the base of the stem starts rotting.
- Pump in plenty of bubbles – Hydro growers use an air pump with airstone to pump tons of bubbles into the water reservoir. This is key to root health as roots need oxygen to survive. It also fights pathogens like algae. I use an Eco Air 2 with 3/16″ ID tubing to connect to a large airstone to provide tons of air for up to two reservoirs.
- Manage the pH (5.5 – 6.5) to prevent deficiencies. Learn how to check and adjust the pH. Make sure to get a pH pen so you can stick it straight in the reservoir and immediately know the pH. I use an Apera A1209 pH pen (it’s very accurate, measures the pH in seconds, and only needs to be calibrated every few grows). But even the cheapest pH Pen works well as long as you calibrate it regularly. One of my favorite things about growing in hydro is that it’s so easy to test and adjust the pH compared to soil or coco. I don’t particularly enjoy testing the pH in soil and coco (you need to test the input, the runoff, etc.) But with hydro testing the pH takes 1 second, is more accurate, and makes me feel like I’m doing science.
Roots are fragile at first, especially when they still look like “feathers”. Don’t move them like this grower did, or roots might get sick.
But once roots ‘harden” they’re extremely tough. You can move them around and they won’t even notice.
If you see green roots, it usually means light is getting into the reservoir. In this case, the lid was so thin it was letting in light. The grower covered the top of the lid with aluminum foil, and light stopped getting to the roots.
Make sure your air pump is making tons of bubbles in the water!
How to Make Hydro Life Even Easier
Here are some bonus tips and tricks to make your life as a hydro grower easier.
Make it easy to move water (Save your back!)
I never pick up my water container. It sits in front of the tent. I use the hose from the bathroom sink to fill it up, add nutrients, then use a water transfer pump to pump it into the reservoir.
- Faucet hose adapter – Stop lugging water around! Get a hose faucet adapter to use a garden hose from the faucet to get water to your grow space.
- Water transfer pump – Use a battery-powered water transfer pump to get your water from in your container to your reservoir. These are also awesome for watering plants directly at the roots (way better than a watering can!).
Use a faucet hose adapter to get water from your sink to your grow space.
Then use a water transfer pump to get water into the reservoir. Never carry water again!
Never worry about spills
- Grow in a grow tent, because they have a waterproof tray at the bottom which can hold many gallons of water. That means if something happens and there’s a spill, none of it will get on your floor. Bonus: if you get a grow tent you can also control smells and you get bigger yields because reflective walls bounce more light onto your plants
10-Gallon Tub or Bigger
For your hydroponic reservoir, use a tub that’s at least 10 gallons or bigger. Considering that you have to leaves several inches of air under the lid, a 10-gallon container holds about 5 gallons of water, which gives the roots tons of room to expand, and you won’t need to add water very often.
A 10-gallon tub or bigger makes your life way easier
- Faster-growing plants and healthier roots
- PH and nutrient levels tend to stay more stable
- Fill up the reservoir less often
Curious to learn more? Let me go a bit deeper into why I recommend bigger tubs for your hydro cannabis plants. Specifically, some of the most popular DWC hydro kits sell you 5-gallon buckets, which can only hold about 2.5 gallons of water, and that’s before your roots get big enough to start displacing the water.
Why a bigger hydro tub instead of pre-made DWC buckets?
When you have the black buckets, they don’t hold enough water, plus you can’t easily test the pH. So you have to take a sample of water from within the bucket, which often involves moving the roots, which you want to avoid if possible
Big hydro DWC tubs like this don’t take much time or maintenance.
In the hydro tub you can easily adjust the pH without moving the plant. You simply need a second port to access the reservoir. That lets you look at the roots, take samples, use your PH or PPM pen, add or remove water, make adjustments, etc. WITHOUT ever having to move the plant.
Extra ports make it easy to check on roots and access water without moving the plant.
Cannabis plants in 5-gallon DWC buckets tend to produce less weed overall. But the real issue is that they don’t hold much water, and by the time plants get bigger, growers often find themselves refilling the buckets daily (or even more often!) to keep the plant from drinking themselves dry.
Cannabis plants in buckets tend to stay smaller.
But the main headache for a cannabis grower is that a 5-gallon hydro bucket doesn’t hold much water and needs to be refilled constantly. There is also no way to easily access the reservoir without having to move the whole plant, and moving roots on a plant is one of the most common triggers for root rot, especially younger plants before their roots “harden”.
This grower moved these plants to bigger tubs because they were drinking the entire reservoir of water in hours.
But don’t these buckets hold 5 gallons? Isn’t that enough?
Even though these are “5 gallon buckets” they cannot be filled to the top. You need to keep the water levels several finger widths below the bottom of the net pot. Then the roots themselves displace the water so you can add even less.
As a results, you can often only add a few gallons of water to these buckets, especially as the roots get bigger.
Check this picture: Notice that the list with the “basket” (called a “net pot”) goes deep into the bucket, and then you have to leave an air gap below that. That doesn’t leave much space for water.
You can only fill up a 5-gallon with a few gallons of water if you want to leave an air gap under the net pot for the fastest, healthiest growth.
10-gallon tubs hold up to 5 gallons of water at a time.
All that root space lets you grow monster DWC cannabis plants!
This Purple Ghost Candy plant produced almost a pound in hydro under a HLG Diablo 350.
But can you grow cannabis plants in little hydro tubs?
Yes, just make sure you can access the reservoir, and keep plants to an appropriate size (not too big).
But just remember, the bigger the tub, the easier your life will be. The smaller the tub, the more time you spend tending to the plants, on average.
Sirius grew this plant in a tiny reservoir under a Spider Farmer 100W LED grow light.
But by harvest, the plant was drinking so much he had to add more water every morning and night.
The small root space, and an early switch to 12/12, ensured the plant stayed small.
A fun project!
Ready to start growing hydroponic weed the DWC way? Check out the full tutorial!
