No matter how much hard work you put into growing your garden, a nitrogen deficiency can stop your plants dead in their tracks. There are several ways to treat nitrogen deficiency in your garden soil, but before you try these methods, it is important to confirm the diagnosis of a nitrogen deficiency.
So, how do you diagnose nitrogen deficiency in plants? A plant with nitrogen deficiency will have yellow leaves on the bottom, and pale green leaves on the top. It will also have poor growth, and any side shoots and branches will be weak and small. However, it is a good idea to do a soil test to confirm nitrogen deficiency.
Let’s take a closer look at the signs and causes of nitrogen deficiency in plants and soil, along with ways you can treat or prevent the problem.
Signs of Nitrogen Deficiency in Plants
There are a couple of obvious signs of nitrogen deficiency in plants: yellow leaves and poor growth. These two symptoms are related, so let’s look at both in turn.
Chlorosis (Yellow Leaves)
Chlorosis is when the leaves of a plant turn yellow, due to lack of chlorophyll (the chemical that makes leaves green). Insufficient nitrogen disrupts a plant’s ability to produce chlorophyll, which eventually leads to yellow or pale green leaves.
Nitrogen is a mobile nutrient, meaning that a plant can easily transport nitrogen between its tissues. So, when a plant has a nitrogen deficiency, it moves nitrogen from the older, lower leaves to the younger, higher leaves on the plant.
A nitrogen deficiency causes the lower leaves to turn yellow first. Later, the higher leaves will turn light green and then yellow.
A plant that cannot produce chlorophyll through photosynthesis will also have trouble producing energy. This will lead to slow growth, thin stems, and weak branches.
This lack of energy and growth can eventually lead to death of the plant, unless the problem is addressed. The first step for doing this is performing a soil test.
Performing a Soil Test
Performing a soil test is really the only way to confirm a nitrogen deficiency in your soil. It is a good idea for two reasons.
First, a soil test will confirm a suspected nitrogen deficiency, which will prevent you from adding nitrogen when your plants don’t need it. After all, other nutrient deficiencies can mimic the symptoms of a nitrogen deficiency.
Second, a soil test will tell you about other problems with your soil. For instance, your soil may have a pH imbalance or a lack of other nutrients, such as phosphorus, potassium, iron, magnesium etc. For more information, check out my article on what a soil test tells you.
As an added benefit, a soil testing lab will often send specific recommendations for treating any problems that your soil may have.
Generally, you will take a soil sample in a bag and send it to the lab (leave the soil out to dry on a tray if it is wet when you take your sample).
Also, be sure to tell the lab what you are growing, so that they can give you more specific recommendations.
Keep in mind that there is a fee for soil testing, depending on where you send it.
For more information, check out my article on soil testing.
Causes of Nitrogen Deficiency in Plants
There are several potential causes of nitrogen deficiency in plants, aside from a lack of nitrogen in the soil. Let’s go over these causes and how they might occur.
If your soil pH is too low (acidic) or too high (alkaline or basic), then it can cause a nitrogen deficiency in your plants. This is true even when there is plenty of nitrogen in the soil!
The reason is that the availability of each nutrient in soil, including nitrogen, depends on the pH of the soil. Outside of an ideal range, nitrogen will become unavailable and the plant’s roots will not be able to absorb it.
For more information, check out this article from Research Gate about nutrient availability by soil pH.
If your soil pH is too low (acidic), you can add lime (calcium carbonate) to your soil to raise the pH. If your soil pH is too high (basic or alkaline), you can add sulfur to your soil to lower the pH. The amounts will depend on the current pH of your soil and the target pH that you want.
Remember that it is always a good idea to do a soil test before adding anything to your soil, to confirm any problem you suspect.
You can buy a soil test kit online or at a garden center, or you can send your soil away to a laboratory at your local agricultural extension to determine the pH of your soil.
A nutrient imbalance in your soil can also cause a nitrogen deficiency in your plants, even if the soil contains enough nitrogen.
For instance, too much carbon in your soil will interfere with a plant’s ability to absorb nitrogen. The level of carbon in soil can be elevated due to sawdust, wood ash, or other carbon-rich sources.
This highlights the importance of soil testing to ensure that you really do have a nitrogen deficiency before adding anything to your soil.
Soil depletion occurs when nutrients are removed by plants as they grow, but not replaced with soil additives. Over the years, this problem can compound to the point where nothing will grow in the soil unless it is allowed to “rest” and remain unplanted for a year or more.
Soil depletion can occur for several reasons. One cause is planting the same crop in the same location every year. If the crop uses up lots of nitrogen, this will lead to nitrogen deficiency over time.
Also, failure to replace nitrogen each growing season will eventually lead to depleted soil and nitrogen deficiency in your plants.
Treatments for Nitrogen Deficiency in Soil
We’ve seen some of the causes of nitrogen deficiency in soil, but how do we treat the problem and prevent it in the future? Here are a few ways to do just that.
Use Crop Rotation
Crop rotation simply means that you plant a crop in a different location in your garden every year. Generally, you will want to rotate crops on a two, three, or four year schedule, depending on the family of the crop.
For instance, one year you might plant one area with nitrogen-fixing plants, like legumes. The next year, you might plant that same area with tomatoes or potatoes (nightshade family), and so forth.
Legumes, such as beans and peas, work with nitrogen-fixing bacteria in the soil, which take nitrogen from the air and turn it into ammonia (which contains nitrogen). This is necessary for the nitrogen to be converted into a form that plants can use.
As a result, legumes do not use as much nitrogen from the soil as other crops. Thus, crop rotation helps to avoid soil depletion and nutrient deficiencies. It also helps to avoid the spread of diseases and pests in your garden.
Plant Winter Cover Crops
Another good way to treat or prevent nitrogen deficiency in your garden soil is by planting winter cover crops. These cover crops may fix nitrogen in the soil, as in the case of legumes like alfalfa and clover.
Some cover crops die over the winter, but either way, you can till the cover crops into the soil. The dead plant material will help to improve the soil by replacing nitrogen and other nutrients consumed in the past year.
As an added benefit, some cover crops can be used to feed livestock if you have horses or cows.
Compost is a great way to replace nitrogen and other nutrients in your garden soil. You can start a compost pile in your yard, either in a bin or out in the open.
Organic material, such as grass, leaves, dead plants, and fruit or vegetable scraps are good candidates for your compost pile. Just be careful about composting weeds, which can come back to life and haunt you.
Also be careful about composting dead plants – it is fine if they died of natural causes, but any diseases or pests can survive for a year or more in your compost pile and cause trouble in your garden later.
When your compost looks decomposed into dark, rich soil, then it is time to add it to your garden. If you have worms in your yard, moving them into your compost pile can help to break down the organic material more quickly.
For more information, check out my article on making your own compost and my article on how to get more worms in your garden.
Manure from animals is another good source of nitrogen for your garden soil. However, to be safe, you should wait until the manure breaks down a bit before adding it to your garden.
If you have your own chickens, cows, horses, or other livestock, you can use their droppings to replenish your soil. If not, you can ask someone who does keep animals, or you can go to a nearby farm or horse-boarding stable and ask about taking manure away for them.
For more information, check out my article on where to find manure.
Blood meal is a soil supplement made from animal blood taken from slaughterhouses. It is a good source of nitrogen, although it is probably better to treat a small area of your garden at a time with this. One method is to put some blood meal into each hole where you intend to put a plant.
You can also use chemical fertilizers to treat nitrogen deficiencies in your garden. The big three nutrients in fertilizer are NPK (nitrogen, phosphorus, and potassium). For more information, check out my article on NPK ratios in fertilizer.
If you have a nitrogen deficiency in your soil, you want a fertilizer where the first number (nitrogen) is high.
A word of caution: be careful about overdoing it with nitrogen fertilizers or other supplements. Too much nitrogen can cause lots of green growth in shoots and leaves, but later on, it may prevent flowering in your plants. No flowers means no fruit and vegetables!
For more information, check out my article on over fertilizing your plants.
By now, you should have an idea of what to look for to identify nitrogen deficiency in your plants. However, a soil test is a good idea, to confirm your suspicions before adding anything to your soil.
I hope this article was helpful. If you have any questions, please leave them in the comments below.