Can You Fertilize Plants Too Much? (3 Symptoms & How To Treat)


A little fertilizer goes a long way, but is there such a thing as too much fertilizer?  I did a little digging to find some information on the subject of over fertilization.

So, can you fertilize plants too much?  It is possible to fertilize your plants too much.  Symptoms include wilted & discolored (yellow/brown) leaves, slow growth, and root rot.  Over fertilization can occur if you use more fertilizer than the package recommends, or if your soil was already high in nutrients or salts to begin with.

Of course, over fertilizing plants can also weaken them and make them more susceptible to pests and diseases. It can also harm the environment by polluting water.

In this article, we’ll start by going into a little more detail about why you see these symptoms in over fertilized plants.  Then, we’ll go over ways to treat over fertilized plants, along with ways to prevent the problem in the future.

Let’s begin.

Can You Fertilize Plants Too Much? (Over Fertilizing)

It is possible to fertilize your plants too much, even if you read the label and follow instructions correctly.  This is because there are other factors that contribute to damage from over fertilizing your plants.

Before we get to that, let’s look at some of the classic symptoms of over fertilization. That way, you can identify the problem when it happens.

Symptoms Of Over Fertilization

There are three basic things to look for to identify over fertilization of your plants:

  • Leaf Appearance (look for the 4 D’s: discolored, dry, drooping, or dropped leaves).
  • Water Level (weak or dead roots means no water uptake, which leads to dry, crispy leaves).
  • Growth (slowed due to lack of water or difficulty in absorbing nutrients).
fertilizer burn on leaf
Look at the leaves to see if they are discolored, dry, drooping, or dropping off.

These symptoms are not guaranteed, but they are a good place to start. Another way to detect over fertilization is to look at the surface of the soil.

If you see a white buildup, you may be looking at excess salt. This can happen due to over fertilization and insufficient watering or poor drainage.

Leaf Appearance Of Over Fertilized Plants

If you fertilize your plants too much, they will end up with what is called fertilizer burn.  According to Wikipedia, fertilizer burn is “leaf scorch resulting from over fertilization, usually referring to excess nitrogen salts”.

When your plants suffer from fertilizer burn, their leaves will become discolored, turning yellow or brown.  This will begin at the edges and then continue to the entire leaf.

nitrogen burn on blueberry plant
This blueberry plant is suffering from fertilizer burn (too much nitrogen). Image from: https://commons.
wikimedia.org/wiki/File:
Blueberry_nitrogen
_burn.JPG

Eventually, the leaves will drop off after they die completely. According to the Penn State University Extension, this leaf damage is more likely to begin on the lower leaves of the plant.

Fewer leaves means less surface area to absorb light for photosynthesis. Together with damaged roots, this will slow the growth of the plant – or kill it entirely.

Water Level Of Over Fertilized Plants

Fertilizer burn occurs in part because excessive salt levels in the soil prevent a plant from absorbing water.  High salt levels in the soil may even cause a plant to lose water through its roots via osmosis (due to the difference in salt concentrations).

wilting cucumber plant
Wilting cucumber plant, courtesy of user Sohmen at Wikimedia Commons. https://commons.
wikimedia.org/wiki/File:
Photo-of-a-real-wilting-cucumber-in-greenhouse.jpg

As a result, a plant affected by fertilizer burn may exhibit some of the classic symptoms of insufficient water, including:

  • Wilted Leaves (they might droop and look “tired” in an attempt to decrease sun exposure to conserve water.)
  • Dry Leaves (they might become “crispy” if the water shortage is severe enough.)
  • Fruit Problems (for example, blossom end rot in tomatoes, since water is needed to absorb calcium and other nutrients.)

Leaf damage due to over fertilization and lack of water will eventually affect the growth of plants as well.

Growth Of Over Fertilized Plants

Over fertilized plants will exhibit slow growth, or they may stop growing entirely.  This can be due to a lack of water due to excess salts or an inability to absorb nutrients due to root damage.

According to the University of Minnesota Extension, too much fertilizer can burn plant roots and may lead to the death of the plant.

However, it is also possible that your plant will continue with excessive green growth, at the expense of flowers or fruit.  This can occur if the plant is receiving too much nitrogen, either from manure or from fertilizer with high levels of nitrogen.

tomato plants with twine rope stake
Tomato plants grow tall and leafy with no flowers or fruit if they get too much nitrogen.

If you think excessive nitrogen in your soil is a concern, check out my article on low-nitrogen fertilizers.

Causes Of Over Fertilization

Some of the major causes of over fertilization include:

  • Using high-nutrient content fertilizers (these fertilizers contain more nutrients and salts per pound).
  • Using fast-release fertilizers (these work faster than other types, but are more likely to burn plants).
  • Ignoring fertilizer package labels (the instructions will tell you how much to use, based on the size of your garden).
  • Adding too much fertilizer at once (it may be better to use less fertilizer at 2 or 3 different times during the season).
  • Poor soil drainage (soil that drains is more likely to leach away nutrients, which prevents over fertilization).

One major cause of over fertilization is using more than the package recommends.  Many beginner gardeners think that more is better, and as a result, they are too generous with fertilizer in the first year.

As mentioned above, this can lead to fertilizer burn, since plants cannot handle the high salt levels in the soil.  However, even if you use the recommended amount of fertilizer, there are still potential problems.

First of all, adding all of the fertilizer at once can lead to sudden drastic changes in the levels of nutrients and salt in the soil.  This shock can harm plants, especially if it occurs during periods of drought, when they are already suffering from a lack of water.

ammonium nitrate
Adding too much fast-release fertilizer at once can burn plants due to the high salt content.

Second, the level of nutrients or salt in your soil may have been too high to begin with.  Even if you add a reasonable amount of fertilizer to your garden, you may still end up with fertilizer burn.

For more information, check out this article from Penn State Extension on the causes of over fertilization.

The best way to avoid this problem is to do a soil test before adding any amendments to your garden.

How To Treat Over Fertilized Plants

There are a few steps you can take to save plants if you think they have been over fertilized.  The actions you take will vary, depending on whether the plants are grown in containers/pots or grown outdoors in the ground.

Treating Potted Plants That Have Been Over Fertilized

First, scrape any excess fertilizer off of the surface of the soil. Remember that white crust we talked about earlier? Wel, that is what you want to remove.

If you haven’t worked the fertilizer pellets into the soil yet, you can usually remove them with a spoon.  Don’t worry if you need to remove some of the soil – you can just replace it with fresh potting mix.

If your potted plants are over fertilized, you may be able to save them by repotting with new soil.

Once you have removed excess fertilizer and salt, water your plant thoroughly to rinse extra salt out of the soil.  You might want to do this with the plant in a sink or outdoors so the water has somewhere to go.

If you know that you used way too much fertilizer and it is hopelessly mixed into the soil (as with liquid fertilizer mixes), then you can try to repot the plant.

First, take the plant and all of its soil out of the pot. Next, remove as much soil as you can from the roots without damaging them.

To do this, brush away the soil gently. Don’t worry if you have to leave a little soil behind on the roots – the important thing is to get rid of most of it.

soil
Use fresh potting mix to replace over fertilized soil for your potted plants.

Then, put a little fresh potting mix in a new container. Put the plant in the container carefully to avoid damaging the roots.

Finally, cover the roots with more fresh potting mix, up to where the plant’s stem was before you took it out of the pot. The plant may still die due to fertilizer burn or transplant shock, but at least it has a better chance to survive now!

Treating Outdoor Plants That Have Been Over Fertilized

First, scrape any excess fertilizer off of the surface of the soil, if you have not worked it in yet.  Otherwise, you may want to remove the top inch or so of soil, and replace it with fresh soil from elsewhere.

Make sure not to remove too much soil. Also, don’t scrape the soil too close to the plant, or else you may disturb the roots or damage the stem or branches.

Then, water thoroughly and deeply all around the plant.  This will give the fertilizer a chance to spread out more evenly into the soil.

watering can
Water the soil around over fertilized plants thoroughly to help dissolve the fertilizer and reduce the local concentration of salt.

Hopefully, the concentration of salts and nutrients will drop. At that point, the plant will not be in danger of fertilizer burn (hopefully).

One caution with this method is that your plant may develop root rot if its roots stand in wet soil for too long.

How To Prevent Over Fertilizing Your Plants

The best way to avoid fertilizer burn and its symptoms is to prevent over fertilization in the first place.  Here are some steps to take to minimize the chances that your plants will suffer from too much fertilizer.

Check Your Plant’s Water Levels First

Remember that fertilizer is not a cure-all!  If your plant looks wilted or droopy, make sure that you are not over watering or under watering.

Often, the symptoms of both of these problems look the same: leaves that are wilted, dry, or curled.

For more information, check out my article on over watering plants.

garden hose
Make sure water levels are correct before adding any fertilizer!

If you are confident that the water levels are fine, then move on to the other steps on this list.

Get A Soil Test

It is good practice to get a soil test before adding anything to your soil, especially fertilizers that are high in nitrogen salts. You can buy a do-it-yourself soil test kit online or in a garden center.

soil test kit
A soil test tells you if a garden has high levels of nutrients.

You can also send a soil sample to your local agricultural extension.  You will get more detailed results this way.

If you tell them what you are growing, you will also get specific recommendations for treating your soil.  For more information, check out my article on how to do a soil test.

Knowing the nitrogen, phosphorus, potassium, and pH levels in your soil will prevent you from adding too much of a good thing when preparing your garden in the spring.

Use Compost First, Then Add Fertilizer As A Supplement Later

Compost has several important benefits for your garden.  It adds organic material, which can help to improve drainage for heavy, sticky clay soil.

Compost also provides nutrients to the soil. This helps to replace the nutrients that your plants use for their growth each year.

compost bin
Compost adds organic material and nutrients to soil, and there is almost no risk of over fertilizing your plants with compost.

In addition, compost adds organic matter to the soil. This attracts organisms (such as earthworms and beneficial bacteria) that will improve the soil for your plants.

The best part about compost is that you can make your own from at home! You can use yard waste and kitchen scraps you already have lying around the house, such as: grass clippings, raked leaves, and vegetable peels.

cutting grass
Use grass clippings as one ingredient in your own homemade compost.

For more information, check out my article on how to make your own compost.

Since fertilizer does not provide organic material to the soil, it should be used as a supplement to compost, instead of as a stand-alone solution for your garden.

Use A Slow-Release Fertilizer

Slow-release fertilizers do not dissolve all at once. As a result, the nutrients do not become available right away.

This prevents the problem of fertilizer burn that we discussed earlier.  It also prevents you from needing to make several applications of fertilizer during the growing season.

The rate of nutrient release depends (in part) on the level of bacterial activity int he soil. You can learn more about slow-release fertilizers (and when to use them) in my article here.

Read & Understand The Fertilizer Label

Make sure that you understand the units being used on the fertilizer label. Also, make sure you have the appropriate measuring tools (measuring tape and scale).

measuring tape
Make sure you have a measuring tape and scale to figure out the area of your garden and the weight of fertilizer required.

The amount of fertilizer is given in terms of weight and area. For example: “5 pounds per 1000 square feet”.

As such, it is important to measure the dimensions (length and width) of your garden accurately, calculate the area correctly (length times width), and measure the weight of fertilizer without guessing.

Measure and add only what is needed – don’t be fooled into thinking more is better!  You can always add more fertilizer later if needed, but it is a lot more difficult to remove it once you have added it and watered it in.

Also, be sure that you understand the three numbers (for example, 10-20-10) on a fertilizer label. If you don’t know what I am talking about, check out my article on NPK ratio in fertilizer.

Don’t Fertilize In Dry Weather (Water In Your Fertilizer)

Avoid fertilizing your garden in dry weather. Try to do it before it rains, so that nature can water in the fertilizer for you. (that is, wash it into the soil and spread out the nutrients to decrease the local concentration of salts).

Sometimes, you must fertilize due to an extended dry spell. In that case, water the fertilizer in with a hose right after you spread the fertilizer.

sandy soil
If you have to fertilize in dry soil during a drought, water the fertilizer in afterwards.

Adding fertilizer without watering can worsen the problem of a lack of water for plants – especially seedlings that are trying to get established.

Conclusion

Now you know how to tell if your plants have been over fertilized and what can cause the problem.  You also have some ideas about how to treat and prevent the problem of over fertilization.

You might also want to read my article on whether you need fertilizer for your garden (and when to use them).

I hope you found this article helpful – if so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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