Organic Phosphorus Fertiliser | Liquid 8% P₂O₅

Overview The Science How to Use FAQ Organic liquid phosphorus fertiliser — 8% P₂O₅ plant-available phosphate feed 8% P₂O₅ 100% in solution Low organic matter No clogging Plant-based Root feed Liquid phosphorus fertiliser supplies 8% P₂O₅ already dissolved in solution, which sidesteps the single biggest problem with phosphorus in the garden: most of the phosphate applied to soil never reaches a root. Phosphorus is the least mobile of the major nutrients, and in British soils it locks up rapidly — bound to calcium on chalky ground, to iron and aluminium on acid ground. Applying it in solution, low, little and often, puts phosphate where roots are actively working rather than leaving it to be fixed in the wider soil volume. Phosphorus is what a plant runs on rather than what it builds with. It is in every molecule of ATP, in the phospholipids of every cell membrane and in the backbone of DNA. Shortage shows up first as a plant that simply does not get going — small, dark, sometimes purple-tinged, rooting badly and flowering late. The organic matter content is deliberately low at 9%, which keeps the solution thin and clean. It passes through drip lines, dosing pumps and fine sprayer nozzles without the residue that heavier organic feeds leave behind. 8%Phosphorus (P₂O₅) 9%Organic matter 3.5 – 4.5pH 1.05 – 1.15Density kg/l What to use liquid phosphate for Establishing transplants and young plants — the period of highest phosphorus demand in the whole life of a plant. Root initiation and early cell division are both phosphorus-hungry, and a seedling checked at this stage rarely fully catches up Root development on cuttings, plugs and bare-root stock — phosphorus drives root branching and fine root production. Apply from the point roots first appear and through the following five to six weeks Flower initiation and fruit set — the transition from vegetative growth to flowering runs on phosphorus. A feed in the run-up to and through bud formation supports set rather than drop Cold spring soils — phosphorus uptake falls sharply below about 12 °C because root activity and mycorrhizal function both slow. A liquid feed bypasses the soil chemistry when the ground is still cold Correcting phosphorus deficiency — stunted growth, unusually dark or dull green foliage, purpling on stems and the undersides of older leaves, delayed flowering Chalky and very alkaline soils — where applied phosphate is quickly bound as insoluble calcium phosphate. Small, frequent liquid doses to the root zone are far more efficient than bulk applications Potatoes and root crops during tuber development — especially on light sandy soils and towards the end of the vegetative stage Liquid phosphate compared with the alternatives Liquid phosphorus 8% P₂O₅ Already in solution — no dissolution step, no waiting on soil chemistry Low organic matter, so it runs clean through drip lines and sprayers Applied little and often to the root zone, where fixation losses are lowest Plant-derived rather than mined or manufactured Acidic at pH 3.5 to 4.5, which helps keep phosphate mobile at the root surface Rock phosphate and bone-based meals Very slow release — measured in seasons rather than weeks Useful for building long-term soil phosphorus reserves Bone-derived products are animal by-products; Dr Forest does not use them Little use for correcting an active deficiency in a growing crop Superphosphate and triple superphosphate Fast-acting mineral phosphate, manufactured by acidulating rock phosphate Highly prone to fixation when broadcast across soil rather than placed No organic matter and no carbon contribution Derived from a finite mined resource with a well-documented supply horizon Do not mix with calcium Phosphate and calcium react in solution to form insoluble calcium phosphate. If you combine this feed with a calcium product — liquid gypsum, liquid calcium, or hard tap water treated with a calcium supplement — you will get a white precipitate, a blocked sprayer and no phosphorus reaching the plant. Apply calcium and phosphorus on separate waterings, at least a day apart. Blended and bottled in small batches in Stockport, Greater Manchester. Plant-based throughout, with no slaughterhouse by-products at any stage. Made by Growers. Backed by Science. The science of phosphorus in plants and soil Phosphorus is the nutrient gardeners most often apply and least often deliver. Estimates of the proportion of applied phosphate taken up by a crop in the year of application sit between 10% and 25%. The rest is fixed into forms plants cannot reach (Hinsinger, 2001; Shen et al., 2011). Phosphorus in soil is rarely absent. It is usually present and unavailable. Why phosphate locks up Phosphate is an anion with a strong affinity for metal cations. Above about pH 7 it precipitates with calcium as increasingly insoluble calcium phosphates. Below about pH 5.5 it binds to iron and aluminium oxides. The window of maximum availability is narrow — roughly pH 6 to 7 — and even inside it, phosphate moves through soil by diffusion alone, at rates measured in millimetres. A root does not find phosphate; phosphate has to be within a millimetre or two of a root hair. What phosphorus does inside the plant 01 Energy transfer Every energy transaction in a plant cell runs through ATP, and the phosphate groups are the energy carrier. Photosynthesis, nutrient uptake and every biosynthetic pathway depend on it (Marschner, 2012). 02 Cell membranes Phospholipids form the bilayer of every membrane in the plant. Cell division cannot proceed without phosphorus, which is why deficiency shows as stunting rather than as a colour change on new growth. 03 Nucleic acids Phosphate forms the structural backbone of DNA and RNA. Rapidly dividing tissue — root tips, shoot meristems, developing seed — has the highest demand. 04 Root architecture Phosphorus availability directly shapes root branching. Under moderate shortage plants invest in more, finer roots to forage; under severe shortage the whole root system is smaller (Shen et al., 2011). 05 Flowering and seed set The shift from vegetative growth to reproduction carries a step change in phosphorus demand. Deficient plants flower late and set poorly. 06 Mycorrhizal partnership Most garden plants acquire a large share of their phosphorus through mycorrhizal fungi, which extend the effective root surface many times over. Very heavy phosphate applications suppress that association (Smith & Read, 2008). Why liquid, and why little and often Fixation is a function of contact between phosphate and soil. Broadcasting dry phosphate across a bed maximises that contact and therefore maximises loss. Delivering a dilute solution directly into the root zone at intervals does the opposite: the phosphate arrives where roots are already working, in a form they can take up immediately, in a quantity small enough to be absorbed before the soil claims it. The acidity helps. At pH 3.5 to 4.5 the applied solution briefly lowers pH in the immediate root zone, which is the same trick roots themselves use — root exudation of organic acids to solubilise bound phosphate is a well-described mechanism (Hinsinger, 2001). A finite resource, and a plant-derived alternative Phosphate rock is a non-renewable mineral resource with no substitute in agriculture, concentrated in a small number of countries. The case for reducing reliance on new extraction is now well established in the literature (Cordell et al., 2009). The phosphorus in this feed is plant-derived. Because the feedstock is real plant material, batch-to-batch nutrient content varies slightly around the 8% specification. Feeding the soil as well as the plant Soil microorganisms mediate a substantial share of phosphorus cycling, mineralising organic phosphorus and solubilising bound inorganic forms (Richardson & Simpson, 2011). Long-run trials show organic and combined organic-mineral fertilisation raising soil enzyme activity substantially over mineral-only regimes — urease by 38.3% and β-glucosidase by 122.4% in one multi-season study (Liu et al., 2021). A plant-derived feed contributes to that system in a way a pure mineral salt does not. References Hinsinger, P. (2001). Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes. Plant and Soil, 237, 173–195. Shen, J. et al. (2011). Phosphorus dynamics: from soil to plant. Plant Physiology, 156(3), 997–1005. Marschner, P. (ed.) (2012). Marschner's Mineral Nutrition of Higher Plants, 3rd edition. Academic Press. Smith, S.E. & Read, D.J. (2008). Mycorrhizal Symbiosis, 3rd edition. Academic Press. Richardson, A.E. & Simpson, R.J. (2011). Soil microorganisms mediating phosphorus availability. Plant Physiology, 156(3), 989–996. Cordell, D., Drangert, J.-O. & White, S. (2009). The story of phosphorus: global food security and food for thought. Global Environmental Change, 19(2), 292–305. Liu, J. et al. (2021). Soil enzyme responses to long-term organic and mineral fertilisation. Chojnacka, K. et al. (2020). Bio-based fertilizers: a practical approach towards circular economy. Bioresource Technology, 295, 122223. How to use liquid phosphorus fertiliser Before you start Measure with a syringe — the doses here are small. The concentrate is acidic at pH 3.5 to 4.5, so avoid skin and eye contact and rinse the measuring kit afterwards. Always dilute into water before applying. This feed is designed for root application rather than foliar spraying. Application rates Root drench — standard feeding Rate 0.5 – 1 ml per litre of water | Frequency every 1 – 2 weeks Delivers roughly 45 to 90 mg/l of P₂O₅, which sits inside the normal range for horticultural fertigation. Use the upper end for establishing transplants and through flower initiation, the lower end for maintenance. Establishment feed — transplants, plugs and cuttings Rate 1 ml per litre of water | Frequency weekly for the first 5 – 6 weeks Start as the first roots develop and continue through establishment. This is the window where phosphorus supply has the greatest effect on the whole season. Flowering and fruit set support Rate 1 ml per litre of water | Frequency weekly through bud formation and set Apply in the run-up to flowering and through the set period, then taper as fruit begins to fill and potassium demand takes over. How these rates were set The source specification gives field rates of 2 to 3 litres per hectare. Converted against typical horticultural water volumes and cross-checked against standard fertigation phosphate concentrations, that lands at 0.5 to 1 ml per litre for garden use. We have stated it in ml per litre because that is the unit a watering can works in. Mixing Half-fill the watering can with water first. Measure the dose with a syringe and add it to the water. Top up to full volume and stir. Apply to the root zone the same day — water the soil, not the leaves. Rinse equipment through with clean water afterwards. When to apply through the season Crop When to apply Vegetables generally From first root development, weekly through vegetative growth and fruit formation Tomatoes, peppers, cucumbers From transplant through to first fruit set, then hand over to a potash feed Top fruit and soft fruit From first leaves or bud break, repeating every 7 to 14 days Potatoes and root crops During tuber development, particularly on sandy soils Ornamentals and bedding Five to six weeks from planting, then weekly through bud formation Cuttings and plugs Weekly from the first roots appearing Never mix with a calcium product Phosphate and calcium precipitate on contact. Do not combine this with liquid gypsum, liquid calcium or any calcium supplement in the same watering can. Separate the two by at least a day. Storage Cap tight, dark and dry, between 10 and 25 °C. Shelf life 18 months to 2 years. Do not let it freeze. What to pair it with Pair this with the rest of the Dr Forest liquid range. Liquid Seaweed Biostimulant covers alginates and natural growth promoters that a straight nutrient feed does not. Liquid Gypsum supplies calcium and sulphur — the two things most liquid feeds leave out. Micro 7 chelated micronutrients fills the trace element gap on long cropping runs. For a full-season plan, see the Dr Forest feeding programme. Liquid phosphorus fertiliser — common questions What is liquid phosphorus fertiliser and what does it do? It is a phosphate feed supplying 8% P₂O₅ in solution. Phosphorus drives energy transfer, cell division, root development and the switch from vegetative growth into flowering. It is the nutrient that gets a young plant established and a mature one flowering on time. Why use a liquid rather than rock phosphate or a dry feed? Dry phosphate applied across soil is largely fixed before roots reach it — bound to calcium on chalky ground or to iron and aluminium on acid ground. A dilute solution delivered into the root zone little and often puts phosphate where roots are working, in a form they can take up straight away. Can I use it as a foliar spray? It is formulated as a root feed and that is how we recommend using it. The source specification gives irrigation rates rather than foliar rates, so we have not published a foliar dilution we cannot stand behind. Why must I keep it away from calcium? Phosphate and calcium react in solution to form insoluble calcium phosphate. Mixed in the same can you get a white precipitate, a blocked sprayer and no phosphorus reaching the plant. Apply the two at least a day apart. How do I know my plants are short of phosphorus? Stunted growth is the first sign, often with foliage that looks unusually dark or dull rather than pale. Purpling on stems and the undersides of older leaves is the classic symptom, though cold weather can produce the same colour without a real deficiency. Late flowering and poor rooting are the other tells. Does it work on chalky soil? This is exactly where it earns its place. On alkaline soil, applied phosphate is rapidly bound as insoluble calcium phosphate, so bulk dry applications are inefficient. Small, frequent liquid doses into the root zone get far more of the phosphorus into the plant. Will it block my drip line or sprayer? No. Organic matter is deliberately low at 9%, which keeps the solution thin and clean. It runs through drip lines, dosing pumps and fine nozzles without residue. Can I mix it with other Dr Forest liquids? It combines fine with seaweed and with the liquid NPK feeds. The one absolute exclusion is calcium in any form. Patch-test if you are combining three or more products. Is it safe around children, pets and wildlife? It is a plant-derived nutrient solution with no animal by-products and no pesticide content. The concentrate is acidic, so keep it capped and out of reach and wash hands after handling. Once diluted and watered in, the treated ground is fine. Is this an organic fertiliser? It is made with organic ingredients and is entirely plant-based, with nutrients and plant-derived throughout. Dr Forest does not hold organic certification for its products, so we say made with organic ingredients rather than certified organic. Why is it acidic? The low pH keeps phosphate soluble and mobile. It also briefly acidifies the immediate root zone on application, which is the same mechanism roots use themselves when they exude organic acids to free up bound phosphate. Where is it made? Blended and bottled in small batches at the Dr Forest workshop in Stockport, Greater Manchester.