What Nutrients Do My Plants Need?

Every single plant requires a balanced combination of nutrients to survive and perform essential functions. Nutrients enable plants to produce healthy, vigorous growth, beautiful blooms, and abundant crops. If the nutrient balance is incorrect, the plant’s health will deteriorate, it will become susceptible to pests and disease, and eventually, it will die.

Plant nutrition is a nuanced science. It’s not enough for the nutrients to simply be present, they must be present in the right amount, and at the right time. Fortunately, plants are great communicators and will let you know when the balance isn’t quite right. Unfortunately, many symptoms of nutrient imbalances and deficiencies are pretty generalised, so it’s helpful for gardeners to have a good knowledge of the principles of plant nutrition.

Here’s a breakdown of the role each nutrient plays, when they’re needed, and signs they may be lacking.

Primary Nutrients - needed in the greatest amounts

Nitrogen (N) is critical for promoting vigorous growth. It also plays a major role in photosynthesis, enabling plants to gain energy from sunlight. Supplement young plants and seedlings with nitrogen, but withhold it from mature crops as it can inhibit fruit production. Sparse, yellowing foliage and slow growth can indicate a nitrogen deficiency (Tajer, 2016).

Phosphorous (P) is essential for healthy root systems, increasing resistance to soil-borne pests and diseases. It promotes blooms on flowering plants and improves the flavour and productivity of crops. Stunted growth, poor yields, and yellow foliage can indicate a phosphorus deficiency. Add a phosphorous-rich feed just before fruiting, or if your plant is being less productive than expected (Sawyer, Creswell, and Tidman, 2000).

Potassium (K) promotes the overall strength of a plant, increases disease resistance, and improves tolerance of harsh weather conditions. Poor flowering or discoloured foliage can indicate a potassium deficiency. Plants need extra potassium just before they begin to flower, but too much potassium can inhibit the absorption of other nutrients (Kaiser and Rosen, 2018).

Secondary Nutrients - needed in moderation

Calcium (Ca) strengthens plant cells and tissue, especially in young plants, and promotes the absorption of other nutrients. Calcium is alkaline, so will neutralise acidic soils, but should be added sparingly to chalky or clay soils (Thor, 2019).

Magnesium (Mg) is a crucial component of chlorophyll, the chemical which is responsible for photosynthesis. Without magnesium, plants cannot gain the energy they need and will suffer from slow growth and yellowing or mottled leaves (Tajer, 2018).

Sulphur (S) aids metabolism and helps plants produce chlorophyll, as well as giving crops such as garlic, mustard, and onions their distinct flavour. The symptoms of sulphur deficiency are similar to those of nitrogen deficiency. Sulphur is acidic, so deficiencies usually only occur in alkaline soils (Van d’Rhys, 2009, Yara, no date). 

Trace Elements - needed in microscopic amounts

The trace elements are Boron (B), Chlorine (CI), Cobalt (Co), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Nickel (Ni), and Zinc (Zn). They perform many essential functions, including the production of chlorophyll, maintenance of metabolic functions, cell and enzyme development, and helping the plant to absorb other nutrients.

Even though trace nutrients are only needed in microscopic amounts, just like primary and secondary nutrients, a lack or excess of any of them can have catastrophic effects (Wade, 2019).