How to Grow Strong Cannabis Roots (and Fix Root Problems)

To grow strong cannabis roots, give them the four things they can't live without: oxygen (an airy medium), mild temperatures of about 18-24 °C (64-75 °F), the right amount of water and the right nutrients, especially phosphorus and calcium. Roots stay out of sight underground, but they play a huge role in how your plant grows and how long it lasts: they anchor it upright and firmly in the soil, and they soak up water and mineral salts.

Roots are a key part of a cannabis plant's digestive system, just like in any other plant: when they aren't fed properly, the plant can develop nutrient deficiencies, a weakness that can be fatal to its immune defenses, and slower growth overall.

What do healthy cannabis roots look like? 

Roots are hard to check on because, well, they live in the growing medium. But if you transplant, you'll notice that healthy roots are milky white and don't have any particular smell. 

Sick roots, on the other hand, are brown, smell bad and have a kind of slime around them. Those are signs of root rot, usually caused by overwatering or poor drainage.

Color isn't the only thing to look for: check how much they've branched out and how much of the medium they've filled.

If you transplant and see the roots haven't taken over the whole container, either you moved the plant too early or the roots aren't developing properly.

How to grow healthy cannabis roots 

For roots to grow properly and be tough enough to carry the plant through every stage, they need four basic essentials: oxygen, the right temperature, water and nutrients.

Get a handle on how much of each is available in the soil and you'll have healthy, thriving roots:

1. Oxygen

It might sound weird, but plants need all the oxygen they can get, because roots breathe. 

So how do they get it? Roots pull oxygen from the growing medium, partly through structures called lenticels, small pores that let gases move between the plant's inner tissue and the outside.

That's why your growing medium needs to be airy, and why we don't recommend clay-heavy or compacted soil. 

Amendments like perlite or vermiculite help aerate the medium, and some growers put a layer of sand at the bottom of the container for the same reason. It all depends on the kind of grow you're running.

If roots don't get enough oxygen, they take up less water and fewer nutrients, start building up toxins and, if the problem drags on, eventually die.

2. Temperature

Cannabis roots always prefer mild temperatures, roughly 18-24 °C (64-75 °F). Indoors, good ventilation is a must: intake, exhaust fans and circulating fans to keep air moving through the grow tent.

Outdoors, mulch or cover crops are a big help. They soften the sun's effects, cut down on evaporation and make it easier to keep temperatures in check. Common mulch options include straw, dry leaves and wood chips.

Another way to keep things cooler is to swap black containers for white ones, or to put shade cloth over your plants.

3. Water

Watering is where a lot of growers get confused. The basic idea: as a plant builds stronger roots and gets bigger, you gradually increase the amount of water.

At first, seedlings need just 50-100 ml (about 2-3 fl oz), and that's plenty for a couple of days. An outdoor plant in flower, on the other hand, can drink 2-5 L (roughly 0.5-1.3 gallons) a day, depending on the container.

But watering isn't just dumping water in, there's a technique to it: water around the stem, but also pour a little just beyond where you figure the roots reach, to coax them into colonizing more space and reaching other nutrients in the medium.

4. Nutrients

They matter a lot, not only because they're the fuel behind vegetative growth and flowering, but also because they help your plants build healthy roots. 

The two key nutrients cannabis needs for its roots are phosphorus and calcium: they play a major role in root development, strengthen the existing roots and push the plant to grow new ones.  

Common root problems and how to fix them 

1. Overwatering and underwatering

Either extreme is bad, and both are classic rookie mistakes. The symptoms? A droopy plant. To figure out which one you're dealing with, check how heavy the container is.

If it's light and the medium is dry, you're underwatering; if it's heavy and the soil has been wet for days, you're overwatering.

The fix is as simple as it gets: water more or water less.

To keep it from happening in the first place, you've got two options. The first is to water with about 1/4 of the container's volume. The second is to weigh the container right after watering and only water again once it has lost 60-75% of the water weight it picked up. 

Overwatering can also come from poor drainage. Make sure your containers have holes in the bottom so excess water can run out. 

2. Overfeeding (nutrient burn)

Fertilizers can be a huge help in getting plants to grow faster and pack on buds that hold their own against anybody's. But overfeeding can seriously damage the roots and stunt their growth.

You'll often hear beginners say the more you feed, the more the plants grow. That's a big mistake: like everything, cannabis can only absorb so much, and going overboard just causes nutrient lockout.

Overfeeding can also come from salts quietly building up at the bottom of the container. One way to catch it is to check your EC (electrical conductivity, a measure of dissolved salts) for salt buildup. In veg, EC should sit between 0.8 and 1.2, and in flower between 1.2 and 2.0. If your plant's readings go past those ranges and it's showing problems, your best move is to flush the roots with at least 4 times the container's volume in water.

Once you see it bouncing back and getting stronger, ease back into your fertilizers gradually, starting with the lowest dose the manufacturer recommends.

3. Root rot: one fix worth trying

Root rot is exactly what it sounds like: sick, rotting roots. It usually happens when harmful bacteria and fungi (like pythium) build up, and they thrive in overwatered soil or standing water.

In seedlings, the main giveaway is a stem that gets very thin; bigger plants wilt, turn yellow and give off a nasty smell.

Unfortunately, plants are hard to save at this point, but it's worth a shot: transplant the affected plant into fresh soil in a sterilized container.

If you notice at transplant time that the plant has few roots, you can help it build out its root system with rooting hormones when you germinate your seeds or plant clones. 

Like every other part of growing and raising a plant, building strong roots is a big deal if you want everything to go right. And like any job, it means paying attention to a handful of factors that can help or hurt your cannabis plant. 

Keep all these tips in mind and grow some spectacular plants. 

How do you make a homemade root stimulator?

1. Cloning: One way to get roots going is cloning. You take a cutting from a mother plant and set it in a special medium that encourages roots to form. You can find cloning kits online or at garden stores.
2. Root soak: This means soaking the plant's roots in a solution of water and nutrients. Fill a container with water and add a high-quality fertilizer, like a commercial root stimulator. Then soak the roots in the solution for several hours before planting it in its final spot.
3. Compost: Compost is a natural way to stimulate root growth. You can make your own at home by mixing organic matter, like food scraps, dry leaves and soil, in a compost bin. Then use it to feed your plants.
4. Rooting hormones: You can buy rooting hormones at garden stores, and they're an effective way to kickstart root growth. Just dip the ends of your cuttings in the hormone solution before planting them in their final spot.

When should you use a root stimulator?

Root stimulators are mainly used in the early stages of a grow, like sowing seeds and transplanting. The main goal is to encourage a healthy root system.

Adding a root stimulator to the growing medium aims to speed up and strengthen rooting in seedlings, so they get established faster and take up nutrients efficiently.

At transplant time, a root stimulator helps reduce stress and encourages new roots, which makes it easier for the plant to adjust to its new home and minimizes transplant shock. And when you propagate from cuttings, it helps clones root quickly and successfully, boosting your odds.

These products usually contain a mix of vitamins, amino acids and plant hormones that stimulate root growth and strengthen the root system.