Something is wrong with your plants. Yellow leaves. Vegetables that won’t ripen, bushes that no longer flower. The sunshine is nominal, and you water everything just right. And yet here you are, eyeing your harvest and asking yourself, What gives? Your plants are trying to tell you with their stunted stalks and lusterless leaves: What gives is a nutrient deficiency. Understanding nutrient deficiencies in plants may mean the difference between your hard work turning into a bumper crop or a withered field.
What is a nutrient deficiency?
Simply put, a nutrient deficiency occurs when a plant is not absorbing enough of an essential nutrient. Usually this occurs because the soil does not have sufficient minerals, but other factors can influence a plant’s ability to absorb nutrients. For instance, cold soil can inhibit the absorption of phosphorous.
Chances are your plants are starved for essential elements. Nutrient deficiencies in plants is the number one reason why harvest yields decline after a few years. As plants mature, they absorb potassium, phosphorous, nitrogen, calcium, and other elements from the soil. Successive crops are forced to grow in less nutrient-rich soil. If the gardener does not replace these essential nutrients with fertilizer, deficiencies are inevitable.
Which nutrients do my plants need?
No matter what you are growing, certain nutrients are universally essential to plant growth. Over a dozen elements have been identified as essential – if the plants don’t have them, you soon won’t have plants.
The three nutrients that plants need in the greatest quantities are: nitrogen (N), phosphorous (P), and potassium (K). Common commercial fertilizer is built on this NPK trio. But other nutrients are as essential as well. Here are some of the lesser known nutrients as well as what plants use them for:
Calcium (Ca) – Essential for new cells and structure
Calcium is a nutrient that you need to watch from the start. Unlike most other nutrients, calcium becomes fixed once the plant uses it. Plants can draw nitrogen, potassium out of dying leaves to use elsewhere. But once calcium is in place, the plant cannot move it.
Magnesium (Mg) — Essential for chlorophyl production.
Plants use chlorophyl to use light energy to convert CO2 and water into oxygen and glucose. Without magnesium, plants cannot create energy, and will soon die.
Cal Mag Deficiency
Magnesium and Calcium have similar chemical properties. They are most often found as carbonates, and have the same chemical charge. Therefore, these two nutrients compete to be absorbed by a plant. Too much of one of these elements may lead to a deficiency in the other. Similarly, soil low on one of these nutrients is likely low on the other.
Sulphur (S)— Seed builder, chlorophyl component, disease resister.
Sulphur interacts with nitrogen to help build proteins and plant oils. Having Sulphur in your soil also helps maintain a healthy ratio of microorganisms.
How to determine which nutrients are deficient in your soil
Whether it’s something common, (such as a nitrogen deficiency or potassium deficiency), or something harder to identify (such, as a magnesium deficiency or calcium deficiency), your plants will give you signals. General signs that appear with most deficiencies include yellowing leaves and stunted new growth. But each nutrient deficiency has a few unique indicators.
Nitrogen: Plants deficient in nitrogen will show symptoms early in their growth cycle. Watch for yellowing or pale leaves, and stunted growth, especially in the stem or new leaves.
Potassium: Potassium deficiencies attack the leaves first. Watch for yellowing or ‘burnt’ edges of older leaves. New shoots will sprout and die.
Phosphorus: Phosphorous symptoms may be hard to spot. Leaves grow darker and duller, especially on the bottom. Leaf tips may curl and brown, and older leaves develop a purple tinge.
Calcium: Calcium deficiency shows in the growth of leaves, buds, and fruits. The tips will be brown, and may feel soft or rotten. The roots will also be poorly developed, and the entire plant may look stunted.
Magnesium: The leaves will yellow, but the veins in the leaf will remain green. Overall growth is stunted.
Sulphur: Similar to nitrogen, a sulphur deficiency turns leaves yellow. In addition, growths will be spindly and stunted.
Thanks to Epic Gardening for their excellent images. Take a look at these pictures to help you know what to look for when identifying deficiencies.
How to fix stunted growth in plants
Knowing there is a problem is only half the battle. Once you’ve decided what the deficiency is, it’s time to fix it. While the basic solution is almost always to add fertilizer, not all fertilizers are the same. Some use organic sources, such as manure, compost, and bone meal, while others are made with chemistry.
For the big three nutrients (nitrogen, phosphorous, and potassium) look for fertilizer that has NPK on it, and then look at the ratio. General purpose fertilizer will say something like 20/20/20, meaning the product is made up of 20% nitrogen, 20% phosphorous, and 20% potassium. Find a fertilizer that is concentrated with the nutrient you need.
Although different plants need slightly different concentrations, here is a good guideline: early in the growing cycle, plants require a great deal of nitrogen; fuel growing blossoms with phosphorous; when forming vegetables or fruit, feed your plants potassium.
For deficiencies in other essential nutrients, shop for specialty fertilizer. These fertilizers may be a bit harder to find, but well worth it.
Calcium can be added by finding a fertilizer that uses lime (calcitic or dolomitic). A good place to brush up on your understanding of calcium deficiencies can be found here.
If you have a magnesium deficiency, look for fertilizer with magnesium sulfate, magnesium oxide, or sulfate of potash magnesium.
Sulphur deficiencies can be fixed with fertilizer containing ammonium sulfate, potassium sulfate, or gypsum
Finding precise nutrient ratios for fertilizer is a deep and innovative science. Growers are experimenting with a range of organic materials to use for their nutrients. But don’t be overwhelmed — just use this article as a checklist when you shop!
The difference between a nutrient burn and a deficiency
An unfortunate irony of horticulture is that adding a multi-nutrient fertilizer to fill one deficiency may result in an excess — a burn — of another. An excess of nutrients results in a browning and curling of leaves’ tips and edges. Look for the tell-tale look of edges appearing burned. Another sign is a blackening of roots, so digging up a plant or two may be necessary to diagnose your nutrient imbalance.
A good harvest comes from the proper ratio of the essential nutrients readily available for your plants to absorb, whether in soil or hydroponics. The chemistry may appear daunting at first, but focus on one or two nutrients at a time, keep a record of any changes in your plants’ appearance, and enjoy the pleasures of helping your garden grow.