What is the correct pH for hydroponics?
This nutrients and additives guide indoor growing is your complete resource for indoor growing success. The correct pH for hydroponics is 5.5–6.1. For coco coir, target 5.8–6.2; for soil, 6.0–6.5. Outside these ranges, nutrients become chemically locked out — producing deficiency symptoms even when nutrients are present in adequate quantities. Always check and adjust pH after all nutrients are mixed, as individual products shift pH significantly.
Understanding plant nutrition is one of the most rewarding aspects of indoor growing — once you grasp how nutrients work and why plants need different things at different stages, the whole process becomes far more intuitive. This guide covers everything from the fundamental building blocks of plant nutrition through to how additives and boosters fit into a complete feeding programme.
The Basics: What Do Plants Actually Need?
Plants manufacture their own food through photosynthesis, converting light, CO2, and water into carbohydrates. But to build all the other compounds they need — proteins, enzymes, hormones, cell walls, chlorophyll — they depend on mineral nutrients taken up through their roots. These break down into three categories:
Macronutrients (NPK)
The three primary macronutrients appear on every nutrient bottle as the NPK ratio:
- Nitrogen (N): The growth nutrient. Nitrogen is the backbone of amino acids and proteins, and the central component of chlorophyll. High nitrogen demand during vegetative growth; reduced demand as plants transition into flowering.
- Phosphorus (P): Energy transfer and root development. Phosphorus is involved in ATP production (the plant’s energy currency) and becomes particularly important during flowering for flower site development and density.
- Potassium (K): Regulation and quality. Potassium manages water movement within the plant, activates many enzymes, and plays a central role in sugar and starch production — important for fruit and flower quality and weight.
Secondary Macronutrients
Calcium, magnesium, and sulphur are needed in significant quantities but appear less prominently on labels. Calcium builds cell walls and is critical for new growth development. Magnesium sits at the centre of every chlorophyll molecule, making it essential for photosynthesis. Both are often undersupplied — particularly in soft water areas or when growing in coco or hydro — which is why a dedicated CalMag supplement is recommended in most programmes.
Micronutrients (Trace Elements)
Iron, manganese, zinc, copper, boron, and molybdenum are needed in very small quantities but are indispensable. Each plays specific roles in enzyme function, hormone production, and metabolic processes. Quality base nutrients supply these in chelated form — chemically bound so they remain plant-available across the pH range rather than locking up in the root zone.
Base Nutrients — The Foundation of Your Feed Programme
Base nutrients supply the full NPK spectrum and should form the backbone of every feed. They come in several formats:
- Two-part systems (A+B): Nutrients split across two bottles that are combined when making up your feed solution. The separation keeps calcium and sulphates apart until they’re diluted — preventing them from reacting and precipitating in the bottle. Examples: Canna Terra Vega/Flores, Dutch Pro Grow/Bloom, Shogun Samurai Grow/Bloom.
- Three-part systems: Micro, Grow, and Bloom components that allow greater control over the nutrient ratios at each stage. The Micro component typically contains chelated trace elements and calcium; Grow and Bloom provide stage-appropriate NPK ratios. Examples: Remo Nutrients Micro/Grow/Bloom.
- One-part nutrients: All-in-one formulas suitable for simpler programmes. Convenient but less flexible — you can’t easily adjust the ratio of individual elements. Better suited to soil grows where the medium provides some buffering.
When choosing a base nutrient, match it to your growing medium. Most brands formulate specifically for soil, coco, or hydro — using the wrong formulation for your medium can create pH instability and nutrient imbalances.
Understanding EC and pH
EC (Electrical Conductivity) and pH are the two measurements that determine whether your plants can actually access the nutrition you’re providing.
EC measures the total dissolved nutrient concentration in your solution. Too low and plants are underfed; too high and roots are under osmotic stress, causing tip burn and growth slow-down. Target EC ranges by growth stage:
- Seedling: 0.6–1.0 EC
- Vegetative: 1.2–1.8 EC
- Flowering: 1.4–2.2 EC
- Flush: <0.6 EC (plain water or very low EC flush solution)
pH determines which nutrients are available for uptake. Outside the correct range, nutrients become chemically locked in forms roots can’t absorb — causing deficiency symptoms despite adequate nutrient levels in the solution. Target pH by medium:
- Soil: 6.0–6.5
- Coco coir: 5.8–6.2
- Hydroponic systems: 5.5–6.1
Always check EC before pH when making up your solution, and adjust pH as the final step after all nutrients and additives are combined.
Feed Schedules — Veg vs Bloom
Most plants require different NPK ratios at different growth stages. Broadly:
- Vegetative stage: Higher nitrogen relative to phosphorus and potassium. Plants are building leaf mass, stem structure, and root systems — all nitrogen-intensive processes. Typical veg NPK might be 3-1-2 or 4-1-2.
- Transition to flower: Begin reducing nitrogen and increasing phosphorus and potassium. Some growers use a specific transition nutrient for this period.
- Flowering stage: Lower nitrogen, higher P and K to drive flower development, density, and essential oil production. Typical bloom NPK might be 1-3-4 or 0-4-5.
- Late bloom / ripening: Many growers further reduce overall EC and increase potassium in the final 1–2 weeks to push ripening and quality.
- Flush: Plain water or a dedicated flush product for the final 3–7 days before harvest, clearing residual salts from the medium and plant tissue.
Additives — What They Do and When to Use Them
Additives are used alongside base nutrients to improve specific aspects of plant performance. The most useful categories:
Root Stimulators and Beneficial Microorganisms
Products like root stimulators, mycorrhizal inoculants, and beneficial bacterial supplements accelerate root development and improve root zone health. Particularly valuable during propagation, after transplanting, and in the early vegetative stage. Dynomyco Mycorrhizal and vitamin B1 supplements like Cyco B1 Boost are standout options in this category.
CalMag Supplements
Calcium and magnesium deficiencies are among the most common problems in indoor growing — especially in coco, hydro, and soft water areas. A dedicated CalMag product like Remo Magnifical or similar should be a standard part of any programme running these media.
Silicon Supplements
Silicon builds cell walls, reducing stretch and improving structural strength. It also improves stress resistance significantly. Products like Aptus Regulator deliver silicon in silicic acid form — the most plant-available form. Use throughout the entire grow at low, consistent doses.
Bloom Boosters and PK Supplements
Bloom boosters supply additional phosphorus and potassium during the flowering period to push flower density, weight, and quality. Options like Plagron Green Sensation and Dutch Pro Explode are all-in-one bloom boosters that replace the need for a separate PK 13/14. Add these from weeks 3–4 of flower through to the final weeks before flush.
Enzyme Products
Enzyme supplements like Canna Cannazym break down dead root matter in the growing medium, reducing pathogen pressure and recycling organic compounds back into plant-available nutrition. Valuable in any organic-containing medium throughout the full growing cycle.
Organic vs Mineral Nutrients
Mineral nutrients are immediately plant-available and predictable — what you put in the tank is what plants get. They’re ideal for coco and hydro where the medium provides no biological buffering. Organic nutrients rely on microbial activity to break down compounds into plant-available forms. They’re slower-acting and harder to dial in precisely, but many growers argue that organic programmes produce superior flavour and aroma in the final product. Soil is the natural home for organic nutrients — the rich microbial ecosystem in quality soil does the conversion work for you.
Frequently Asked Questions
Frequently Asked Questions
The correct pH for hydroponics is 5.5–6.1. For coco coir, target 5.8–6.2; for soil, 6.0–6.5. Outside these ranges, nutrients become chemically locked out — producing deficiency symptoms even when nutrients are present in adequate quantities. Always check and adjust pH after all nutrients are mixed, as individual products shift pH significantly.
Overfeeding shows as burnt leaf tips, darkening leaf colour, and reduced growth. Underfeeding shows as pale yellow-green leaves starting in older growth first, and slow overall development. Before adjusting your nutrient dose, always check pH first — the vast majority of apparent deficiency symptoms in hydro and coco are caused by incorrect pH locking out available nutrients rather than actual nutrient absence.
No — base nutrients and additives from different brands are generally compatible provided you check EC after mixing and avoid duplicating the same nutrient. Using one brand for your base ensures the ratios are designed to work together, but mixing additives from different brands is common practice and works well.
In soil, alternate between nutrient solution and plain water every other watering — this prevents salt build-up and lets the medium contribute its own reserves. In coco and hydro, feed at every single watering without exception, as inert media have zero nutrient reserves and plants depend entirely on what is in your solution.
We stock a comprehensive range of leading nutrient brands including Canna, Dutch Pro, Plagron, Remo Nutrients, Aptus, Rock Nutrients, Cyco, and many more. Browse our full nutrients range online, or contact us for a personalised feeding programme recommendation based on your growing medium and setup.
For official horticultural guidance and growing tips, the Royal Horticultural Society (RHS) is an excellent resource for gardeners and indoor growers.
Further Reading
- The Biobizz Feeding Chart for Soil Growers
- Fish Sh!t Organic Soil Conditioner — The Complete Guide
- Biobizz Fish-Mix — The Expert Growers Guide
- Can You Use Hydro Nutrients in Soil?
- How to Use Aptus Regulator
- How to Use Dutch Pro Explode
- How to Use Rock Resinator
- How to Use Plagron Green Sensation
- How to Use Plagron Promix
- How to Use Remo Grow
- How to Use Remo Micro
- How to Use Remo Magnifical
- How to Use Canna Terra Professional Plus
- How to Use Cyco B1 Boost
- How to Use Canna Cannazym
- How to Use Dynomyco Mycorrhizal
- The Plant Magic Feed Charts
- The Mills Feeding Chart
- The Buddhas Tree Feed Chart
- The Hydrotops Feed Chart
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