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You know the old saying about having too much of a good thing. It’s true, and can be applied in many ways to gardening. In particular, having the right amount of fertilizer can make your plants thrive in lush greenery, but having too much is not good for them.
Excess fertilizer will damage your plants, and leave them with “fertilizer burn” which can eventually kill them if you don’t know how to fix it.
What is Fertilizer Burn?
Though it’s common to refer to this condition as “burn,” it isn’t really about heat or even light. When there is a chemical imbalance, it can effect the way water moves in and out of the plant’s tissues, especially the roots.
In this case, water flows out of the plant by osmosis, towards the high concentrations of fertilizer compounds, leaving you with plant tissue that is dehydrated. Symptoms are described more below.
Any type of fertilizer can harm your plants when there is too much of it, but you generally find fertilizer burn when you have excess nitrogen.
This is why you are not supposed to use fresh manure as food for your plants. It is too high in nitrogen, and is a common cause of fertilizer burn. The nitrogen breaks down naturally over time, so manure should be aged at least 3 months before application.
Signs of Fertilizer Burn on Plants
So what should you be looking for? As with most plant ailments, the symptoms aren’t that specific and can be mistaken for other issues. You may want to rule out other potential problems before investigating about fertilizer burn.
Before you start to see any real damage or problems, you might notice that your plants are getting more leafy than usual, or possibly not putting out flowers like you would expect.
That’s the first natural response to high nitrogen levels in the soil. It might seem great at first if you are growing plants for their foliage, but it will soon stop looking to lush.
Leaves will turn yellow, wilt and get brown along the edges, looking very much like they’ve been scorched by high heat. Fertilizer burn isn’t something that will happen naturally, so if you haven’t added anything to the soil, you are probably looking at another problem.
Treating Your Plants
Once you pinpoint your problem, it’s time to take some steps to bring your plants back up to health.
Are we talking about indoor houseplants? Then, the main way to fix fertilizer burn is to flush the soil out with water. Add enough water to flow through the potting mix and let it wash right out (not just collect in the pot tray). You may even need to repot the plants in fresh soil.
It can be tougher treating outdoor plants because you aren’t working with such a controlled soil situation. Extra watering can help but unless you have really good drainage, you do run the risk of drowning your plants in the process.
If you are unable to save your plants, you will have to just replant and start again (with new fertilizer wisdom). Before you do, give the effected garden bed several thorough waterings to flush out the nitrogen before adding new plants.
Having too much nitrogen isn’t exactly like dealing with pH. You can’t just add something else to the soil to “neutralize” the nitrogen. It needs to be washed out.
Proper Fertilizer Use
You can avoid this problem by understanding the nature of fertilizer and how to properly apply it. As we already mentioned, you do want plenty of nitrogen if you are growing plants for their foliage, but look to higher phosphorus amounts for all of your flowering or fruiting plants (that includes vegetables like tomatoes or cucumber too).
Are you following the directions? This refers to the commercial products obviously. You probably will have to dilute your product before you apply, and the instructions may tell you that you need to further water your plants at a certain point after fertilizing. Ignore these details, and you can have problems.
Don’t fertilize when not necessary. It’s easy to assume that all plants need a feeding now and again, but now that you know you can overdo it, you should make sure your soil needs it in the first place.
Test kits from the garden store are inexpensive and an easy way to see what your plants really need.
Sources of Nitrogen
Fertilizer burn can be caused by any sort of nutrient chemical, but nitrogen is the most likely culprit. It can be very helpful to know which fertilizers have nitrogen in the first place so you can avoid overdoing it.
This is especially a concern when using natural fertilizers that don’t have precise ingredient lists or ratios on the label.
It is very easy to use two or three natural materials because they each offer something to the soil (like potassium or calcium) and not realize that each one is also giving a fat dose of nitrogen at the same time. Some examples are:
- Any type of manure, especially horse or cow
- Alfalfa meal
- Cottonseed meal
- Blood meal
- Seaweed emulsions
So if you are combining two or more of these in your fertilizing regimen, you might be overdoing the nitrogen without realizing it.
This can also be a problem when you are using a commercial product, if you don’t know what the labeling means. Some fertilizers will be labeled with the type of plant they are intended for, like grass, tomatoes or African violets.
This isn’t very helpful if you are trying to find the right mixture for a plant not named.
So look to the set of three numbers that should be on every product. Something like 10-10-10. The first number stands for nitrogen, the next is for phosphorus and then potassium (also known as N-P-K).
Are you using a product with that first number higher than the others, something like 16-4-8? Try switching to 5-5-5 or another blend with less nitrogen from now on.
The best way to deal with fertilizer burn is to be aware of your product choices and to avoid it in the first place.