How Nutrient Lockout Occurs in Weed and How to Save Your Crop

All you need to know about this common problem


If your plant looks limp and fragile and the leaves have changed to an unnatural and unhealthy-looking color, there is a strong possibility that it is suffering from nutrient lockout, sometimes shortened to ‘nutrient lock.’ It happens when your marijuana plants are unable to utilize the nutrients in the growing medium.

Novice growers are often shocked when it happens to them. After all, they have been feeding their plants regularly, so how can their weed be struggling to grow? What they fail to realize is that nutrient deficiency and nutrient lockout are two different things, but can affect plants in similar ways. Lockout normally happens because of these two reasons:

  • Unsuitable pH Levels in the water & soil: The pH of your growing medium must be within a certain range. If it isn’t, your plants become unable to take up the nutrients you feed it.
  • Overfeeding: This issue often causes a pH imbalance. When you provide your plants with too many nutrients, it has a negative effect on their ability to use them. Chemical fertilizers have a high salt content, and this contributes to the issue. Occasionally, excess nutrients bind together or become incompatible, which means the plant can’t use them.

If your plants are experiencing nutrient lockout, you must act fast to make the nutrients accessible. Otherwise, your plants will begin to suffer from nutrient deficiency and die. In this guide, we show you how to spot the problem, and fix it right away.

Nutrient Lockout Signs and Symptoms

Marijuana plants require numerous nutrients to grow and thrive. Aside from the ‘big three’ nutrients – Nitrogen, Phosphorus, and Potassium – your crop needs so-called secondary nutrients and micronutrients such as Iron, Zinc, Copper, Manganese, Magnesium, and Cobalt.

If your plant has nutrient lockout, it can’t absorb these nutrients which lie in wait in the root zone. While it can happen in every growing medium, the most susceptible are coco noir, soil, and rockwool. If you use too much chemical fertilizer, which commonly has a high salt content, you end up with a situation where an excess of a single nutrient causes the lockout of other nutrients.

pH imbalance remains a mystery to novice growers. The pH system is a measure of a substance’s alkalinity or acidity. The pH scale ranges from 0-14. 0 is the level of the most acidic substances on the table, 14 is the level of the most alkaline, while 7.0 is pH neutral and is the value given to pure water.

If soil is your growing medium, the correct pH range is between 6.0 and 6.8. If you are using a hydroponics system, the right range is between 5.5 and 6.5. Your first duty is to monitor the pH of the water you use. If it is too alkaline, you encourage the growth of algae. If it is too acidic, you can ‘burn’ your crop.

Advanced growers invest in a Reverse Osmosis (RO) water system to handle that side of things. The amount of nutrients you add to your plants also alters the pH. Nitrogen, for example, is very much on the acidic side. When you add it to pH neutral water, it should bring the pH down to the right level.

If you are using a hydroponics setup, plan out your nutrient program. Expert growers break their feeding plans into several parts to allow for the natural changes to a plant’s diet as it grows. For instance, marijuana plants need far less Nitrogen in the flowering stage than they do when in the vegetative stage.

It isn’t easy to identify lockout, primarily because it shares many of the same symptoms as nutrient deficiency. For example, yellowing or curling of the leaves is an issue associated with both. It is normal for your plants to look ‘underfed’, which may cause novices to provide even more nutrients and exacerbate the issue.

Generally speaking, plants with nutrient lockout look weak, and growth has stagnated. If you fail to take action, the yellow color turns to brown, and the leaves will start curling up – they could even look burned!

How to Fix Nutrient Lockout in Cannabis

It is at this stage that keeping a feeding journal comes in handy. If you take this practical step, you will be able to check your notes to see if you are dosing the nutrients correctly. If you use salt-based fertilizers and are not using the right combination or quantity of nutrients, salt build-up happens fast.

In my experience, the instructions on store-bought nutrients tend to err on the side of overfeeding for obvious reasons. When growing marijuana, especially for the first time, use approximately half of the recommended dose, to begin with. If it turns out that your nutrient mixture is okay, the next step is to measure the soil’s pH.

Invest in a reliable pH meter, and if the reading is outside of the ideal range, you need to stop feeding the plants, and flush them and growing medium with fresh pH balanced water. This process will fix the salt build-up and allow your plants to gain access to nutrients. There are also special products for raising or lowering pH.

Preventing a Nutrient Lockout

As is the case with the world in general, prevention is better than cure when it comes to nutrient lockout. Here are three ways to ensure it doesn’t become a problem in the future.

Regular pH Checks

This is especially the case when growing in a hydroponic setup because you’re in control of feeding, and more likely to overfeed than if your plants grow in soil. A pH meter is an inexpensive, yet invaluable, device. You should check pH levels at least once a day, if not more.
Use pH Up if your soil is too acidic, or pH Down if it is too alkaline. Alternatively, use lime to increase the pH or sulfur to decrease it.

Always Use Organic Nutrients

As well as being a better choice for the environment, organic nutrients will not cause a salt build-up. In contrast, chemical fertilizers are salt-based, which increases the likelihood of a nutrient lockout.

Flush Your Cannabis Plants

Don’t wait until nutrient lockout occurs before flushing, do it at any stage when your plants are particularly hungry, and you are forced to feed them heavily. Choose a specific day, and make sure humidity in the grow room is below 50%. Flushing overwaters the root zone, which has the potential to harm the roots, so tread carefully.

pH balanced water is essential when flushing your plants. The excess water running through the growing medium breaks down the salt buildup. After the flush, the soil is saturated. Wait until it is dry before resuming feeding. If you don’t allow the soil to dry properly, you risk the development of root rot. Water the garden normally for a few days and reintroduce nutrients.

No matter the cannabis plant issue, you must learn from the experience. As crucial as it is to identify and solve nutrient lockout, knowing how to prevent it from happening in the future is more important. Whenever you plan to change your nutrient plan, do it gradually. Check the pH of your growing medium regularly, and flush whenever necessary; just make sure you don’t do it within a couple of days before harvesting the crop.