Plants need to eat! Both water and nutrition are important for plants and understanding how plants take up nutrients and what each of the nutrients does means that you can grow healthy plants year after year. Not all plants are looking for nutrients at the same level, and some promote leaf growth while others promote fruit growth. In this article we will teach you which nutrients your plants are looking for, what they do, and what it looks like when they are short on nutrients.
Plant nutrition is a science, specifically from how a plant cell works, how plants take up nutrients and how they use them. I’m not going to go into that in this article because it isn’t important for a newer gardener, however knowing the nutrients that plants need and how it affects them is vital, regardless of how long you’ve been gardening for.
Without proper nutrition, plants can’t grow. Similar to us as humans, we need nutrients to stay healthy and feel good. When your soil is low in one specific nutrient or mineral, your plant will show signs of this deficiency. One of the most difficult parts of plant nutrition is that some nutrient deficiencies can look like others, so it requires time, patience and trial and error to learn about this topic.
By the end of this article you should have a better idea of what each nutrient does, how it affects the plants, how some plants like certain nutrients more than others and how to keep your soil filled with their favourite foods.
Before we get into the details of each nutrient it’s important to know that there are two groups of nutrients; macro and micro nutrients. The difference between macronutrients and micronutrients is based on how much your plant needs them. Therefore, macronutrients are labelled as that because your plant needs them in greater quantities than the micronutrients.
When your soil is healthy, all of these nutrients should be present – however if you don’t maintain your soil properly it can run out of these nutrients, leading to issues. Therefore, it’s important to ensure that you are caring for your soil from the beginning of the season all the way through to closing it down.
Macronutrients are the most common nutrients that you’ve heard of and are the main nutrients labelled on any fertilizers you buy, organic or not. There are actually 9 macronutrients but the most common ones are N-P-K which is nitrogen, phosphorous and potassium.
Nitrogen is the most famous of all of the macronutrients, for good reason. Nitrogen is a crucial ingredient for plant growth. It’s also the primary ingredient in popular synthetic fertilizers because it’s the key to green leaves and quick growth. When gardeners use these popular fertilizers they believe that it works well and it’s a quality product because of this massive growth. But nitrogen is not the only nutrient plants need, and having too much nitrogen can actually be an issue.
A quick little history of nitrogen. Nitrogen in the air is unavailable for plants, and creating synthetic nitrogen was an extremely difficult task that took science a long time to accomplish. However, in 1909 scientists were able to convert atmospheric nitrogen into ammonia, which is what is used by our plants. Sadly, this discovery also led to highly explosive and damaging bombs that were used in the First World War.
When nitrogen is too high it will promote quick growth in your plants. This quick growth is noticeable in tender leaves, which are a target for aphids. So using too much nitrogen can actually hinder your garden by bringing in pests in high numbers.
Plants that benefit from higher nitrogen include the leafy vegetables, since this is what nitrogen is good for, and some heavy feeders like celery. Plants that don’t benefit from high nitrogen include those that “root”, “shoot” or “fruit” such as carrots, broccoli and tomatoes.
There are great ways to add nitrogen to your soil that are organic and natural since synthetic fertilizers are harmful for the planet from production to application. The most common way to add nitrogen to your soil is by applying manure – with chicken manure having the highest nitrogen content. Be mindful not to add too much manure to your garden because high nitrogen can also burn your plants. A soil test is a great way to check your nutrient levels before applying any top dressings to your garden.
Nitrogen is mobile, which means that plants can move it to anywhere they need to. Therefore, yellowing in older leaves is a sign of low nitrogen since it robs the nitrogen from older leaves in order to grow new leaves. Be mindful that plants will also yellow old leaves as they age and die off and this is a natural cycle. Recognizing the difference is important. To fix low nitrogen, add a higher nitrogen fertilizer to your plants. Start in small quantities and add more as required because you don’t want to add too much if you misdiagnosed the issue.
Phosphorous is important for plant growth. It plays a similar role that nitrogen does so it’s important to ensure you have enough in your soil.
Currently in the farming world there is an overuse of phosphorous which is bad on the soil and the waterways. Farming practices currently are set up to over-fertilize with phosphorous because it gets tied up in the soil. However, along with the reduction of tree lines on farmlands and erosion from heavy rains, loads of phosphorous end up in waterways, leading to algae-blooms. Nitrogen runoff also plays a key role in these algae-blooms which can be deadly for water life and even your beloved pet. Therefore, it’s important to look for organic or natural phosphorous fertilizers and apply it only when necessary.
Because phosphorous is critical for plant growth, most plants benefit from it. Since it’s essential for root growth and flowering, any plant that flowers will benefit; from fruit to tomatoes, to legume plants. Also plants that grow in cold weather with smaller roots and larger top growth (like lettuce) benefit from phosphorous.
Organic ways to add phosphorous to your soil include manure and compost, or you can buy commercial phosphorous since it is mined from the earth. However, I highly recommend sticking to manure or compost, or homemade fertilizers from weeds, alfalfa or comfrey before choosing to purchase commercial fertilizer. And as I mentioned above, doing a soil test will help you determine if you need phosphorous once you’ve topped up with quality compost or manure.
In younger plants, phosphorous deficiency presents as stunted growth. However, if your plant is at a larger size it can show as a lack of blooms and reduced growth in roots.
Potassium is a key nutrient for moving water around your plant. It’s also critical for the formation of starch which is used for the movement and storage of sugars. It also helps with root growth and photosynthesis. Potassium plays a larger role in overall plant growth, but you can see from the above list why it’s such an important nutrient.
Potassium is better able to be taken up by plants when the soil moisture is high. Therefore, the drier your soil, the more issues you may have with potassium deficiency.
Plants that benefit from potassium include those that are fruiting such as tomatoes. One researcher also suggests that potassium is important in sugar levels of watermelon. This makes sense since potassium is important for the movement and storage of sugars. Other vegetables that benefit from potassium include cantaloupe, strawberries, beans, peas and edamame.
Organic ways to bring potassium into your garden include compost, manure, and wood ash. However, if you regularly care for your soil through topping up, mulching and watering, your potassium levels should be less of a concern. As stated before, a soil test will help you determine if you have an issue with potassium.
Similar to nitrogen, potassium is mobile in your plants. So when potassium is low, older leaves will have dead spots in them from dead cells. Also, since potassium is key for moving water around, wilted plants can also be a sign of low potassium since it regulates the stomata (the “mouthes” of the plant that let water out of the plant if they don’t operate properly)
There are 9 micronutrients that your plants need, and although they aren’t mentioned often, your plants can still suffer from micronutrient deficiencies. The above photo shows an example of low iron in a cucumber plant where you can see the leaves are yellow but the veins are green. The second photo is of a green cucumber plant that is being grown in the same year, but in different soil. Store bought soil kits don’t test for micronutrients, so if you test for the three major macronutrients and their levels are fine but you still suspect a nutrient deficiency in your soil, send your soil off to your nearest extension office or university for them to test your soil.
Learning about the varieties of plants that your growing will help you understand when you’re dealing with a nutrient issue or not. For example in the photo above there is a pepper plant that is white and green. This is a perfect example of a plant that has variegated leaves. This is a specific feature of this plant and doesn’t signal a nutrient deficiency. Similarly, in the photo below you can see the zucchini plant with white leaves. This is also a variegated plant with similar features. Next to the zucchini you will see a tomato plant with curled leaves. You may think that this could be a nutrient issue, however this is a plant response to too much water (and sometimes too much sun). As you continue to grow a garden, and are curious about your plants, you’ll learn to identify the difference between a nutrient deficiency and other issues.
Maintaining healthy soil is key to keeping your plants healthy. The more you care for the soil, the less external fertilizers you will need to add. And with properly maintained soil, you shouldn’t need any synthetic fertilizers at all.
Water regularly, top up your garden with quality compost or manure each season, mulch each year and your soil will thank you.
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