Buyers Guide to Plant Nutrition and Fertilisers

Choosing the right fertiliser is essential for healthy plant growth in indoor environments. Whether growing in soil, coco coir, or hydroponics, plants require a balanced mix of macronutrients, micronutrients, and beneficial additives to thrive. Understanding how different products contribute to plant health can help growers optimise their feeding schedules for strong roots, vigorous growth, and high yields.

In outdoor environments, most of these elements are available to plants organically through soil and other natural processes. However, when growing plants indoors, especially hydroponically or in coco coir, it’s up to you to use the right mixture of plant nutrients at the right time to ensure healthy growth and to improve the performance of your plants.

Keeping it simple is a great place to start when it comes to plant fertilisation, so we’d highly recommend beginners or those new to growing indoors to stick to one fertiliser brand’s growth schedule, as the majority of time this will lead to good results.

There are a multitude of beneficial additives that can be used to aid plant growth, and when used correctly can really aid plant growth and health, and ultimately, increase the quality and/or quantity of your harvest. As always, if there’s anything you’re unsure of please get in touch.

Types of Fertilisers & Additives

Base (NPK) Nutrients

Base nutrients provide essential macronutrients (Nitrogen, Phosphorus, and Potassium - NPK) along with vital micronutrients. They form the foundation of plant feeding, supporting vegetative growth and flowering. Available in grow (higher nitrogen) and bloom (higher phosphorus and potassium) formulas, they ensure plants receive the necessary nutrients at each stage.

Root Boosters & Stimulants (Including Mycorrhizal Additives)

Root stimulants encourage strong root development, improving nutrient and water uptake. They often contain beneficial microbes, enzymes, and mycorrhizal fungi, which establish symbiotic relationships with roots to enhance growth. These additives lead to better resistance against stress, stronger plants, and improved nutrient absorption.

Growth & Bloom Stimulants

Growth stimulants contain hormones, seaweed extracts, and plant bio-stimulants that promote faster vegetative development. Bloom stimulants focus on flower and fruit production, helping plants reach their full yield potential by boosting metabolic activity and nutrient uptake.

PK Boosters

PK Boosters provide high levels of phosphorus and potassium to enhance flowering and fruiting. These nutrients increase bud size, density, and essential oil production, making them vital for maximising yields in flowering plants.

Calcium & Magnesium (Ca/Mg) Additives

Calcium and magnesium are crucial for strong cell walls, chlorophyll production, and enzyme activation. Coco coir and hydroponic growers often require additional Ca/Mg supplements to prevent deficiencies that cause yellowing leaves, weak stems, and poor flowering.

Flush Products

Flushing solutions help remove excess nutrients and salts from the growing medium, preventing nutrient lockout and build-up. Used before harvest, they enhance flavour and quality by eliminating unwanted residues from the plant’s system.

Silicon Additives

Silicon strengthens cell walls, making plants more resistant to pests, diseases, and environmental stress. It also improves root structure and nutrient uptake, leading to stronger stems that can carry heavier flowers and fruits, and better overall plant health.

Vitamin/Amino Acid Additives

These additives improve stress tolerance, root development, and nutrient absorption. Amino acids act as building blocks for proteins, aiding in faster growth and recovery, while vitamins help support enzymatic functions and metabolic processes.

Beneficial Microbes & Enzymes

As mentioned above, beneficial microbes, such as mycorrhizal fungi and rhizobacteria, promote root health and nutrient absorption. Enzymes help break down dead roots and organic matter, keeping the root zone clean and free from harmful pathogens.

By selecting the right combination of fertilisers and additives, growers can optimise plant health, boost yields, and prevent deficiencies, ensuring a successful indoor grow, time and time again. 

Non-mineral elements

Three of the key elements needed by plants; Hydrogen, Carbon, and Oxygen, are readily available through fresh air and water. The rest need to be provided by you, the grower, throughout the plant growth cycle.

Macronutrients (NPK)

Macronutrients play a huge and vital role in plant development and they are required in large quantities to ensure healthy growth.

Plants need three primary macronutrients (NPK) in varying amounts:

• Nitrogen (N) – Essential for leafy growth and chlorophyll production. This macro element is an essential component of all proteins and is necessary to ensure the formation of chlorophyll, amino acids, and co-enzymes.
• Phosphorus (P) – Supports root development, flowering, and fruiting. A macro element known to be vital in sugar, phosphate, and energy production, Phosphorus serves several functions and is particularly important in the flowering and fruiting stages, as well as for stimulating root growth.
• Potassium (K) – Aids in overall plant health, stress resistance, and flowering. This element is required in large amounts for protein synthesis. Potassium helps in the manufacture of essential sugars and starches, and it also encourages plants to grow healthy roots and a sturdy structure.

The ratio of these nutrients varies depending on the plant’s growth stage:

• Vegetative growth requires higher nitrogen.
• Flowering and fruiting plants need more phosphorus and potassium.

Other important secondary macro nutrients required are Calcium (Ca), Magnesium (Mg), and Sulphur (S). Silicon (Si) is also a macro nutrient used by plants, and whilst it is not considered essential for plant health in flowering plants for example, it is proven to provide many benefits, including increasing plant resistance to pests and disease, increasing cell wall and stem strength all whilst helping to increase nutrient uptake - all very beneficial when growing large flowers/fruits/vegetables.

• Calcium (Ca) - Calcium aids the formation of healthy cell walls and activates required enzymes. It also plays a role in photosynthesis and regulates the transport of other key nutrients.
• Magnesium (Mg) - This macro nutrient is a vital part of chlorophyll. It also is needed to make oxygen during photosynthesis and is important for catalysing the growth process.
• Sulphur (S) - This essential element plays a key role in the formation of chloroplasts and protein synthesis. It helps with water uptake and during the seeding, and flowering / fruiting stages of plant growth. Sulphur also acts as an organic fungicide which is beneficial throughout the entire growth cycle.
• Silicon (Si) - Although considered a beneficial element, silicon has a role in many vital plant functions. It is known to protect plants from pests and disease, it strengthens cell walls and increases plant health and productivity, and is shown to improve root mass and overall yields.

Micronutrients

These elements are required in smaller quantities by plants but they are equally important to healthy plant growth as the macro nutrients themselves. Iron, Molybdenum, Boron, Copper, Manganese, and Zinc are all types of micro element. There are a few other elements that can be considered as ‘trace’ elements. These are elements that plants need in very small amounts, and can normally be found in the base nutrient of each brand.

• Boron (B) - Boron serves a primary function in cell wall formation, but secondary functions include sugar transport, cell division, and the synthesising of a number of key enzymes.
• Iron (Fe) - Iron is a necessary element for photosynthesis and is also a required element for the synthesis of chlorophyll; both processes are essential for healthy plant growth.
• Molybdenum (Mb) - This micronutrient plays a role in enzyme production and in building amino acids, all of which can stimulate plant growth and increase health.
• Copper (Cu) - Copper is a micro nutrient that plays several key roles in plant development. It is important and necessary for photosynthesis; it is involved with many enzyme processes, and helps form cell walls and sturdy plant structures.
• Manganese (Mn) - This element plays a role in photosynthesis and is also important in the building of chloroplasts.
• Zinc (Zn) - Zinc is a basic constituent of many plant enzymes and it also plays a key role in the formation of chlorophyll and nitrogen metabolism.
• Selenium (Se) - Another beneficial element, selenium has been shown to help plants in several ways, such as increasing water retention during drought, increasing tolerance to oxidative stress, protecting plants against pests, and delaying senescence (the process of aging and death).
• Sodium (Na) - Although sodium is considered a beneficial element and not an essential element, it still helps plants thrive and it can act as a substitute for potassium for some plant functions, such as enzyme activation and photosynthesis.

Spotting Deficiencies and Over-Fertilisation

If you’re not using the correct mix of nutrients on your plants then chances are at some point sooner or later they will develop some form of element deficiency, or toxicity. The good thing however, is your plant will show you! When a plant isn’t receiving enough/receiving too much of one or more of the chemical elements it needs it can often be spotted visually on the plant itself, and more specifically, their leaves. The affected leaf age (new or old growth), where on the leaf itself (tip(s)/base, vein), and the size, shape and colour of the spot/spotting can all give vital clues as to what the potential problem may be. Most importantly, once the deficiency/problem has been correctly diagnosed, the solution is often a simple case of increasing the dosage on the plant(s) next feed(s). 

If you know what you’re looking for with nutrient deficiencies then you’ll know what you’ll need to do to bring your plants back to full health. Deficiencies only arise with the essential chemical elements and the beneficial elements silicon, sodium, cobalt and selenium will not cause a noticeable deficiency if your plants are not receiving them.

Nitrogen (N) deficiency appears as pale yellowing of older leaves, slow growth, and weak stems. When over-fertilised, plants develop dark green leaves, become weak and stretched, and show signs of leaf tip burn.

Phosphorus (P) deficiency results in purple or reddish stems, slow growth, and dark green leaves that eventually turn brown. Overuse can lead to leaf curling, excessive root growth at the expense of foliage, and nutrient lockout.

Potassium (K) deficiency causes yellow or brown edges on leaves, weak stems, and reduced resistance to pests and disease. Excess potassium can cause burnt leaf edges, crinkled leaves, and deficiencies in magnesium and calcium.

Calcium (Ca) deficiency results in deformed new growth, curling leaves, and a weak root structure. When over-applied, calcium can lead to stunted growth and nutrient lockout, affecting the uptake of other essential elements.

Magnesium (Mg) deficiency is seen as yellowing between the veins of older leaves (interveinal chlorosis), eventually leading to leaf drop. Overuse of magnesium can cause dark green leaves with brown spots and trigger calcium deficiency.

Sulphur (S) deficiency leads to yellowing in new growth, weak stems, and slowed development. Too much sulphur can cause leaf tip burn and, in extreme cases, premature leaf drop.

Iron (Fe) deficiency results in yellowing between veins on young leaves, stunted growth, and poor overall development. Over-fertilisation with iron is rare but can cause unnaturally dark leaves and nutrient lockout.

Zinc (Zn) deficiency appears as yellowing between veins, misshapen leaves, and short internodal spacing. Excess zinc can result in leaf tip burn and slow growth.

Copper (Cu) deficiency causes pale yellowing, weak stems, and leaves that may take on a bluish-green tint. Too much copper is uncommon but can lead to toxicity, causing leaf wilting and plant stress.

Manganese (Mn) deficiency results in yellowing between leaf veins and the appearance of dead spots. Overuse of manganese can cause brown spotting and premature leaf drop.

Boron (B) deficiency leads to deformed new growth, brittle stems, and poor flowering. Excess boron can cause leaf tip burn and poor root development, hindering nutrient uptake.

Molybdenum (Mo) deficiency manifests as yellowing leaves, poor nitrogen uptake, and curling foliage. Over-fertilisation is rare but can interfere with the absorption of other essential nutrients.