effects of too much fertilizer on plants

Every gardener knows that 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 research on the subject of over fertilization. So, can you fertilize plants too much? Yes, you can fertilize your plants too much. Symptoms of too much fertilizer include wilted and discolored (yellow or brown) leaves, along with slow growth and root rot. Over fertilization of plants can occur if you use more fertilizer than the package recommends, or if your soil was already high in certain nutrients or salts to begin with. Let’s start off by going into a little more detail on 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. 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 so that you can identify the problem. Symptoms Of Over Fertilization There are three basic things to look for to identify over fertilization of your plants: leaf appearance, water level, and growth. Of course, you can always look at the surface of the soil – if you see a white buildup, you may be looking at excess salt caused by over fertilization and insufficient watering or 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”. This blueberry plant is suffering from fertilizer burn (too much nitrogen). Image from: https://commons.wikimedia.org/wiki/File:Blueberry_nitrogen_burn.JPG For more information, check out this article from Wikipedia on Fertilizer Burn. 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. Eventually, the leaves will drop off as they die completely. If you are worried about excessive nitrogen in your soil, check out my article on low-nitrogen fertilizers. Water Level Of Over Fertilized Plants Fertilizer burn occurs because the 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. As a result, a plant affected by fertilizer burn may exhibit some of the classic symptoms of insufficient water. These symptoms include leaves that are wilted (droopy) and dry (crispy). 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 You may also see some symptoms on the fruit of some plants. For instance, tomatoes may exhibit blossom end rot, characterized by a brown or black spot on the bottom of the fruit. This may occur due to uneven water availability to due excessive salt from fertilizer. Growth Of Over Fertilized Plants Over fertilized plants may 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 rot. However, it is also possible that your plant will continue with green growth, at the expense of flowers or fruit. This can occur if the plant is receiving too much nitrogen, either from manure or fertilizer with high levels of nitrogen. Causes Of Over Fertilization One major cause of over fertilization is using more than the package recommends. Many beginner gardeners think that more is better, and so 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. 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. 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. If you haven’t worked in the pellets yet, you can usually remove them with a spoon. If you need to remove any soil, you can replace it with fresh potting mix. If you see a white buildup on the surface of the soil, remove it along with some of the soil. As mentioned earlier, this can be a sign of excess salt buildup. 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 that 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. Remove the plant from the pot and get as much soil as you can from the roots without damaging them. If your plant has fertilizer burn, you can try to repot it with fresh potting mix to save it. Then, put a little fresh potting mix in new container, put the plant in without damaging the roots, and then cover with more fresh potting mix. The plant may still die due to fertilizer burn or transplant shock, but at least it has a chance to survive! 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, and don’t go to 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. Hopefully, the concentration of salts and nutrients will drop low enough that the plant will not be in danger of fertilizer burn. 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 the problems of fertilizer burn and other problems 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. Make sure water levels are correct before adding any fertilizer! If you are confident that the water levels are fine, then move on to 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. You can also send a soil sample to your local agricultural extension. You will get more detailed results this way. You will also get specific recommendations for treating your soil, as long as you tell them what you are trying to grow. For more information, check out my article on how to do a soil test. Knowing the levels of nitrogen, phosphorus, potassium, and other nutrients in your soil will prevent you from adding too much of a good thing when preparing your garden in the spring. Use Compost First, And 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 clay soils. Compost adds organic material and nutrients to soil, and there is almost no risk of over fertilizing your plants with compost. Compost also provides nutrients to the soil, replacing what your plants remove as they grow each year. The best part about compost is that you can make your own from things you have lying around anyway, such as grass clippings, raked leaves, and food scraps. 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. For more information, check out my article on how to make your own compost. Use A Slow-Release Fertilizer These fertilizers do not dissolve all at once, and so 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. Read And Understand The Fertilizer Label Make sure that you understand the units being used on the fertilizer label, and that you have the appropriate measuring tools (measuring tape and scale). The amount of fertilizer is often given in terms of area, such as “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 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 When you fertilize your garden, be sure to water it in right away, or do it before a rain storm so that nature can do it for you. Fertilizing during a dry spell can worsen the problem of a lack of water for plants, especially seedlings that are trying to get established. Conclusion By 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. I hope you found this article helpful – if so, please share it with someone who can use the information. If you have any questions or advice of your own about over fertilized plants, please leave a comment below.