Even when you provide the best that a plant needs – water, light, nutrition, sometimes you’ll notice that things aren’t the way they should be.
A common problem is the discolouration along the margins of your leaves. While this could be one of many things – the primary cause for this is excessive nutrients!
Proper plant growth requires a balancing act of about 16 different macronutrients and micronutrients. If a plant receives too much of any of these, it can get nutrient burn.
In hydroponic systems, nutrient burn often occurs when the levels of fertiliser salts—measured by electrical conductivity (EC)—are too high. Excessive nutrients are harder to control in most hydro systems because all the plants are exposed to the same nutrient solution.
Excess nutrient accumulation doesn’t always show up as burns on the leaves, however. Too much nitrogen may in fact make the plant look temporarily lush and full of foliage while its fruits prematurely drop and the roots shrivel up, leading to death in the plant.
Sometimes, this discolouration will travel along the edges of the leaf to its base. (The excess nutrients accumulate at the ends of the leaf because they can’t travel any further.) The brown is sometimes separated from the healthy, green plant tissue by a halo-like yellow margin.
In addition to this, nutrient burn can also occur when fertiliser levels are on point. In this case, the plant is stressed by other factors, such as pests or diseases, and cannot utilise all the nutrients that it is provided with.
It’s important to note that when in the leaves, nutrient burn looks like a condition known as leaf scorch. Leaf scorch is caused by water leaving the leaves via respiration faster than the plant can replace it, such as during extremely hot, sunny weather. Coincidentally, nutrient burn is exacerbated by hot, dry weather, making the identification of symptoms more challenging.
Another issue that looks like nutrient burn can occur if the plants are grown under grow lights. If they are too close to the light source, the tips of the leaves can burn. The solution in this case is to either raise the lights or move the plants a bit further away from the heat source.
Different types of plants present symptoms of burn differently depending on which nutrient or nutrient combination caused problem. Typically, however, a plant with nutrient burn will develop brown or dead spots along the leaf tips.
3. Fixing and Avoiding Nutrient Burn
Thankfully, it is possible to bring your plants back from nutrient burn. The brown on the margins of the leaves is not going to turn green again, but new leaf growth should be unaffected if all goes well.
When nutrient burn occurs, the excess nutrients need to be flushed out or removed entirely and the proper ratio of nutrients needs to be re-established. If nutrient burn occurs in a hydroponic system, drain the water from all of the reservoirs and refill with clean water. Let the system run for 24 hours with the new water, then assess the EC level. If it still seems high, drain the system, refill again, and test after another 24 hours. Repeat the process until the EC is at an acceptable level.
Once the excess nutrients are flushed out, determine what caused the problem if you can. If it is not immediately obvious, reduce the amount of fertiliser you would normally apply by half.
If burn symptoms do not reappear, keep incrementally raising the amount of nutrients that you feed your crops. Do this until normal levels have been reestablished and no further symptoms of nutrient burn arise.
Also, remember that different types of crops have different nutrient needs. In general, leaf crops like lettuces and spinach, as well as many herbs, require higher amounts of nitrogen; crops that are grown for their fruit, including tomatoes, peppers, eggplants, and cucumbers, should maintain relatively lower nitrogen levels; and crops that are grown for their roots, such as carrots, parsnips, and radishes, need higher amounts of potassium.
Crops in different phases of development have differing nutrient needs, too, so it’s important to know what your plant needs the most of when it is in a vegetative phase or a bloom phase. Also, crops that are grown indoors or under artificial light have different nutrient needs than those grown outdoors.
In general, plants tend to need more nitrogen when they receive full daylight or are exposed to high levels of artificial light. When natural light levels are lower during late fall and winter months, most fruit-producing plants need more potassium. The ratio of potassium to nitrogen can be raised to twice its usual amount during the winter months, and returned to its usual ratio in the spring.
So, there you have it. Nutrient burn is a common, fixable issue that even the most devoted plant parents can run into. Once your plants are back on track, just be sure to learn from your mistakes and stop smothering your little ones with too much love before you both get burned again.