Just about every gardener has come across nitrogen toxicity at some point. You may not have recognized it as such at the time, but it was there nonetheless. Also known as “the claw”, nitrogen toxicity can present itself in many ways, including shrivelled, yellowing leaves and plant death. Read on to learn how to recognize it, treat it, and prevent it in future.
Hydroponics can be an easy way to grow a variety of plants in a controlled setting. After all, it’s fun and effective method. There’s a catch, however: the hydroponic learning curve can feel a bit overwhelming. When it comes to balancing nutrients, hydroponics can feel more like a chemistry lab than a garden.
Things start out so easy, plants looking lush and healthy. The greenhouse is practically overflowing with vivid leaves and abundant foliage. But those leaves are looking a bit too vivid, aren’t they? You look at the roots, and suddenly your plants don’t seem as healthy. Flowers and fruits are scarce and undersized. Then, leaves start withering and dropping off.
What’s happening? Nitrogen toxicity has struck again.
You see, while preparing the proper solution for your plants is relatively easy, it’s not always straightforward. Different plants have different needs, and balancing those needs is sometimes tougher than it sounds. Like any form of gardening, hydroponic gardens can be either over- or under-fertilized.
One of the benefits of hydroponic gardening is that you start with a blank slate: water. Unlike soil, which could be rich or poor, sandy or clay, water is simple. It offers hydration and nothing else. The rest comes from you. Whatever you mix into the water becomes your growing medium.
This controlled environment can cause problems when your growing solution is unbalanced. Maybe you misread measurements or entrusted your greenhouse to your brother for a week. Or, it could be that the solution you purchased isn’t quite ideal for the plants in your garden. Whatever the cause might have been, the plants are suffering. If you want to save your plants, you have to restore the balance.
Nitrogen and New Growth
Plants need nitrogen in order to thrive. In fact, this nutrient is absolutely essential to healthy growth. The amount of nitrogen, however, varies depending on the stage of growth, and the plant variety.
Nitrogen is a major component of the compound chlorophyll, which is what gives plants their green hues. Furthermore, this chemical gives tender young plants the energy to grow, and helps them convert light into energy.
Plants need a lot of nitrogen at the beginning of their life cycle, when they’re spending a lot of energy building healthy stems and leaves. Like raising puppies, sometimes it feels like all you do is feed your little plants and watch them grow.
After the vegetative growth stage, young plants start working on producing flowers and fruit. When that happens, plants need more balanced nutrient feeds. Potassium is one of the most essential nutrients for flower production. If the solution is too heavy in nitrogen, potassium levels will be inadequate, thus delaying the flowering period.
In fact, your plants may fail to flower altogether.
If you don’t even out the nitrogen with proper amounts of phosphorus and potassium, your plants can’t won’t be able to produce anything. Furthermore, they could end up dying from nitrogen toxicity.
Know the Signs of Nitrogen Toxicity
How can you tell if your plants are getting too much nitrogen? Late-stage nitrogen toxicity is easy to recognize:
The edges of your plants’ leaves will turn brown and crisp. In addition, they may begin to curl in on themselves. These burned edges are a sign that your plants have been getting too much nitrogen for a while now. They need you to take immediate action.
If your plants have been getting too much nitrogen and too little of other essential nutrients, the leaves will turn dull yellow. They may feel dry as well. It you don’t correct your solution quickly, these yellow leaves will drop off. Once the leaves fall off, the plant’s recovery is highly unlikely.
What about early signs of nitrogen toxicity? How can you catch it before these extreme signs appear?
Keep a close eye on leaf color and root size. Get to know what the right color is for your leaves and you don’t let lush leaves fool you. It looks great to see a lot of lush, dark green leaves, but this is exactly why early nitrogen toxicity often goes uncorrected.
The best early indicator of unhealthy nitrogen levels is darker than average leaves. If you start to see your leaves turn dark, especially if the plant seems late in flowering, check your balance.
These classic signs of nitrogen toxicity are helpful tools, but can indicate a number of different health issues. Before you balance the nutrient levels, make sure the issue is actually nitrogen toxicity.
If you’re growing hydroponically, you don’t have to worry about under-watering. You do have to make sure that your solution is being oxygenated, though. If you don’t have air stones or some form of aeration, add them in to allow oxygen into the mix.
Another potential issue is with pH levels. If the growing solution’s pH balance is off, you could be mistaking signs of an acidic or overly alkaline solution for nitrogen toxicity.
Last of all, make sure your plants aren’t just too hot or too cold. If you’ve been letting a winter chill sink in, leaving grow lights off, or cranking the heat, your plants may just be suffering from extreme temperature variations.
If all these possibilities check out, however, you can be certain the problem is nitrogen. So let’s work on correcting that toxicity!
Repairing the Damage
Once you know the cause, treating nitrogen toxicity is relatively easy. The first step, is to dilute your solution with water to lessen the amount of nitrogen. You may need to drain and replace the solution entirely, but for now, just do a bit of damage control.
Diluting the solution is a great way to see if your overall balance is off. If dilution solves the problem, it’s likely that the nutrient balance is good, but the ratio of nutrients to water is off. Keep that in mind as you move forward. Your plants may just be a bit thirstier than you’d expected.
Remember to calibrate your system’s pH level after dilution. An ideal pH for most hydroponic crops is between 5.5 and 6.5. Adjusting the water may neutralize your pH too much, so keep an eye on that.
Refresh and Re-evaluate
If dilution doesn’t help, especially if nutrient levels look good but toxicity symptoms remain, you’ll have to refresh your reservoir. This is a tricky situation, since you still can’t be sure what exactly cause the toxicity. Draining and refreshing the reservoir gives your plants a chance to start on a clean slate.
Drain the reservoir, then fill it back up with fresh water and fresh nutrients. Go a little lighter on the nitrogen to start, but don’t deprive your plants of this essential nutrient entirely.
Your plants are overwhelmed with nitrogen right now, so going from feast to fast may help them heal faster. Just be careful and attentive. Keep nitrogen levels in the solution at a minimal level, or at least on the low end of normal for at least a few weeks.
When your plants seem to be fully recovered, you can go back to average nitrogen use. Some gardens choose to stay cautious, however, and only give a full measure of nitrogen in the early, vegetative growth period.
If your plant’s leaves have already curled and yellowed significnatly, it’s unlikely that they’ll recover. Leaves that have been burned by excessive nitrogen rarely return to a healthy state. That said, you can remove the yellow, curled leaves and give the plant a chance to heal what it can. The plant itself may heal within a week, if you’ve caught it quickly, but deeper damage may take longer to heal.
Plants will be delayed in flowering and producing fruits until they’ve had a chance to recover fully. If they do end up producing flowers, expect smaller, less vibrant ones. In fact, don’t be surprised if plants that have experienced nitrogen toxicity are always a bit behind other plants. They’ve been through a pretty big trauma. This doesn’t mean they’re not going to be healthy and productive eventually, they will. But healing takes time.
The good news is that if you’re gentle with your plants, they do have the potential to recover. Nitrogen toxicity is repairable, except in very severe cases. It may take a few weeks, or even a couple months to see results. Just try not to worry, and don’t try to rush the process. In the end, you’ll have gained a lot of knowledge and lost only a few leaves in the process.