Dr Forest
Strawberry Fertiliser | Organic High Potash
Strawberry Fertiliser | Organic High Potash
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Strawberry Fertiliser 3-2-7 — designed for sweetness, aroma and berry quality
Most strawberry fertilisers push foliage. This one is designed around flavour. The 3-2-7 NPK ratio — with potassium at more than twice the nitrogen level — drives sugar accumulation, ester biosynthesis and anthocyanin production in developing berries. Nineteen ingredients including Yorkshire Polyhalite at 21% of the blend, Scottish Seaweed, Gypsum, Alfalfa Meal and EM-1 Microorganisms deliver a complete slow-release feed with 7.2% calcium from four sources for firmer, longer-lasting fruit. Handcrafted in Stockport — no slaughterhouse waste.
Nitrogen is deliberately moderate at 3% — sufficient for healthy crown and runner development without the excess that dilutes Brix, suppresses volatile production and produces soft, watery berries. The K:N ratio of 2.4:1 sits firmly in the range the literature identifies as optimal for strawberry flavour and sensory quality.
What this formula does for your strawberries
- Sweeter, more aromatic berries — chloride-free potassium from Yorkshire Polyhalite and SOP drives phloem loading of sucrose into developing fruit, the primary mechanism of Brix, sweetness and ester production
- Deeper colour, higher anthocyanins — high K and sulphur from Polyhalite stimulate the phenylpropanoid pathway responsible for the red pigments and antioxidants that define a ripe strawberry
- Firmer berries, longer shelf life — 7.2% calcium from four sources strengthens cell walls in developing fruit, reducing softening, bruising and post-harvest deterioration by 15–25%
- Stronger crowns, better fruit set — phosphorus from Phosphorous Meal and Micronised Rock Phosphate supports root development and flower initiation for uniform, well-set berries
- Living soil biology — EM-1 Microorganisms, Fermented Biochar and Mealworm Frass chitin build the competitive microbial community that suppresses Botrytis and crown rot while producing secondary metabolites linked to improved flavour
- Trace mineral depth — Scottish Seaweed, Volcanic Rock Dust and Clay Minerals supply the enzyme cofactors for volatile ester biosynthesis — the fruity, floral compounds that make a properly grown strawberry smell and taste complex
Dr Forest Strawberry vs general-purpose feed
Dr Forest Strawberry Fertiliser 3-2-7
- 19 ingredients — 7.2% Ca, 2.5% Mg and broad trace minerals
- K:N ratio of 2.4:1 — optimised for sugar and volatile production
- Slow-release organic fractions feed for weeks per application
- 7.2% calcium for firm berries and longer shelf life
- Living biology from EM-1, biochar and mealworm frass
- Apply every 4–6 weeks — not weekly
General-Purpose or High-N Feed
- Excess nitrogen produces large, watery berries with diluted flavour
- Low or no calcium — soft fruit, rapid post-harvest deterioration
- No trace minerals — the enzyme cofactors for aroma volatiles are absent
- No soil biology — soluble salts suppress beneficial organisms
- Feast-and-famine nutrient cycle with weekly dosing
- Salt and EC build-up in containers and raised beds
Dr Forest fertilisers are blended in small batches from traceable British ingredients. Named after Joe's grandfather — an NHS GP who believed in doing things properly. No slaughterhouse waste. No shortcuts.
All 19 ingredients — what they do and why they are in the formula
Every ingredient is here for a specific, research-backed reason. Nothing is filler. Yorkshire Polyhalite is the largest single ingredient at 21% of the blend — this is a potassium-led formula designed around flavour.
Yorkshire Polyhalite — North Yorkshire, slow release 50–60 days
The largest ingredient at 21% of the blend. Supplies K, Ca, Mg and S from a single crystal mined 1,200m below the North Sea. The sulphur fraction drives anthocyanin biosynthesis and flavour volatile production. Extends K supply for 50–60 days — the sustained background that keeps sugar loading active through the entire fruiting season.
Nitrogen Plant Extract — Plant-derived, controlled release
The primary nitrogen carrier at 12% N. Mineralises over 6–8 weeks without nitrate spikes. For strawberries, controlled nitrogen is critical — excess N produces lush foliage, soft watery fruit, diluted Brix and suppressed volatile ester production.
Alfalfa Meal — Plant-based, slow release, biostimulant
Contains triacontanol — a natural growth regulator that increases chlorophyll content by 15–20%. More photosynthate means more sucrose available for transport into developing berries. Also supplies 2.5% N and trace minerals. At 10% of the blend, one of the largest ingredients.
Gypsum (Calcium Sulphate) — Mineral, immediate release
23.3% calcium and 18.6% sulphur in immediately plant-available sulphate form. Calcium is immobile in the phloem — it must be continuously supplied to developing fruit. Strengthens cell walls for firmer berries with longer shelf life. Delivers Ca without raising soil pH — important for strawberries which prefer pH 5.5–6.5.
Sulphate of Potash (SOP) — Mineral, immediate release
Fast-acting potassium at 50% K₂O — chloride-free. Activates sugar transport, anthocyanin production and volatile ester biosynthesis immediately. Bridges the gap from day one while Polyhalite's slower K release builds through the season.
Epsom Salt (Magnesium Sulphate) — Mineral, immediate release
The fastest-acting magnesium source at 17.7% Mg in immediately plant-available sulphate form. Magnesium is the central atom of every chlorophyll molecule. Addresses interveinal chlorosis within days — critical during rapid spring growth when Mg demand peaks. Sulphur fraction supports flavour volatile production.
Phosphorous Meal — Plant-derived, fast-moderate release
Organic phosphorus at 15% P and 9% Ca for root development, crown establishment and flower initiation. Undergoes rapid microbial breakdown, releasing P within weeks at the two most critical moments: root establishment after planting and bud initiation before flowering.
Scottish Seaweed Meal — Hand-harvested
Over 60 trace elements including zinc, iron, manganese and boron. Natural cytokinins delay leaf senescence — extending the productive season. Betaines improve osmotic adjustment under drought and heat stress. Alginates improve soil structure around the shallow root zone.
Fermented Biochar — British, activated
At 2% of the blend, creates permanent porous carbon scaffold housing beneficial microorganisms. Increases plant-available K retention by 18–35% under leaching conditions — particularly valuable in containers and raised beds where strawberries are commonly grown.
Micronised Rock Phosphate — Mineral, slow reserve
The most concentrated P and Ca source at 31% P and 46% Ca. Dissolves slowly as a long-term reserve. Handles the late-season P demand when everbearing varieties are still setting fruit in August and September.
Humic Acid & Fulvic Acid — Mineral organic, chelation
Chelates micronutrients, increases soil bacterial biomass by 30–60%, stimulates mycorrhizal colonisation by 25–40%. Fulvic acid increases nutrient uptake during the rapid fruiting phase. Research shows 15–30% higher Brix in humic acid-treated strawberry trials.
Rapeseed Meal — British, slow release
Steady nitrogen over 6–8 weeks through microbial breakdown. Acts as a prebiotic carbon source. The gradual mineralisation avoids the nitrate spikes that suppress volatile ester production and dilute berry flavour.
Mealworm Frass — Sustainably reared, SAR activator
Contains chitin. Plants detect it as a pest signal and upregulate Systemic Acquired Resistance, priming defences against Botrytis (grey mould), powdery mildew and crown rot — the three most common strawberry diseases in the UK.
Clay Minerals — British, permanent CEC reservoir
Montmorillonite and illite clays. Ionic reservoirs that bind and slowly release K, Ca and Mg between waterings. Valuable in the light, well-drained soils and container mixes where strawberries perform best.
Seaweed Extracts — British coastal, biostimulant
Concentrated cytokinins, betaines and mannitol. Enhances nutrient uptake, flower set and fruit development under stress. Research shows foliar seaweed extract can boost strawberry yield by up to 65% under stress conditions.
Volcanic Rock Dust (Basalt) — Mineral, trace elements
Zinc, iron, copper, manganese — the enzyme cofactors for volatile ester biosynthesis. The fruity, floral compounds (methyl butyrate, hexyl acetate, furaneol) that define a properly grown strawberry require these trace minerals as catalysts.
EM-1 Microorganisms — Living culture
Bacteria, yeasts, actinomycetes and lactic acid bacteria. Suppresses Botrytis and crown rot through competitive exclusion. Produces bioactive compounds that enhance secondary metabolite production — the flavour and aroma compounds in developing berries.
Silica Meal — Mineral, structural
Silicon strengthens epidermal cell walls — a physical barrier against powdery mildew spore germination and aphid stylet penetration. Improves leaf rigidity and fruit firmness. Silicon is not present in most UK garden soils at sufficient concentrations.
Herbal Mixture — Plant-derived, biostimulant
Comfrey (K-rich, rapid breakdown), nettle (iron, silica), yarrow (phosphorus-solubilising bacteria), chamomile (rhizobacteria support). Broad-spectrum biological stimulus for the shallow strawberry root zone.
How to use: rates, timing & method
Apply to the soil surface and incorporate lightly into the top 5–10cm only. Deep incorporation is unnecessary and can damage the shallow fibrous root system. Always leave a 10cm gap from the crown to prevent burn. Water thoroughly after every application.
Soil preparation — before planting
Beds and raised beds
100g/m² in fertile soil or for light-feeding alpine types. 130g/m² for average garden soil. 170g/m² for maximum flavour in new beds or when pushing sweetness and aroma to the peak — this rate delivers a strong potassium foundation for the season.
Single plants at planting
Leave a 10cm gap from the crown. 15g for small transplants or alpine types. 25–30g for established crowns. 40g for maximum flavour — concentrates potassium in the root zone for peak sugar and ester production.
Containers, pots and hanging baskets
5g/L if using mycorrhizal fungi inoculant (lower P avoids suppressing colonisation). 10g/L in plain compost without mycorrhizal fungi.
Feeding — ongoing through the season
Early spring as growth resumes, or 4–6 weeks after planting once established. Apply every 4–6 weeks during the growing season — focus on pre-flowering and fruiting stages for maximum sweetness. Reduce or stop after the main harvest to avoid excess foliage.
Rows and beds — top-dressing
80g/m for maintenance and light-feeding varieties. 120g/m for standard feeding. 160g/m during peak fruiting for maximum sweetness and aroma. Spread evenly along the row. Lightly scratch in. Water well. Avoid direct contact with crowns.
Single plants — top-dressing
15g for light feeders. 25–30g for standard feeding. 40g during peak fruiting for maximum flavour. Apply in a ring 10–15cm from the crown. Incorporate lightly. Water in.
Containers and pots — top-dressing
1g/L for light feeders and alpine types. 2g/L for standard feeding. 3g/L during peak fruiting for maximum sweetness and aroma — this is the rate that pushes K delivery into the peak volatile and sugar production zone. Apply to compost surface. Scratch in lightly. Water thoroughly.
3 level teaspoons = 1 tablespoon ≈ 15g. We recommend mixing the fertiliser with an equal volume of compost before application — this reduces dust, coats the granules in microbe-rich compost, and supports the living biology for enhanced flavour compounds.
Use Dr Forest Seaweed Powder as a fortnightly foliar spray — boosts volatile production and stress tolerance without extra nitrogen. Apply Dr Forest Liquid Gypsum as a root drench every 2–4 weeks for additional calcium and firmer berries. Apply mycorrhizal fungi inoculant at planting for improved nutrient uptake and yield.
Cool, dry place out of direct sunlight. Keep sealed between uses. Effective for at least 18 months.
Strawberry growing guide — varieties, planting, runners & feeding by type
Not all strawberries grow the same way. The distinction between June-bearing, everbearing and day-neutral varieties is the most important factor in how you feed, manage and harvest your plants.
Feeding adjustments by variety type
June-bearing — Elsanta, Cambridge Favourite, Honeoye, Hapil, Florence, Sonata
One concentrated flush over 2–4 weeks in June–July. Feed in early spring as growth resumes, again just before flowering, and once more immediately after harvest to build reserves for next year's crowns. Stop feeding by late August. The post-harvest feed is as important as the pre-flowering feed — it funds next year's flower buds.
Everbearing — Flamenco, Buddy, Finesse, Malling Allure
Multiple flushes from June through to October. Lighter, more frequent feeding keeps potassium supply steady without nitrogen spikes between flushes. The 3-2-7 formula's sustained K from Polyhalite is particularly well-suited to everbearing varieties — it maintains sugar loading across the extended season.
Day-neutral — Albion, Seascape, San Andreas, Sweet Ann
Fruit continuously regardless of day length. Similar management to everbearing but with even lighter individual applications. Monitor for lush foliage and adjust downward — these varieties are sensitive to excess nitrogen.
Alpine — Alexandria, Mignonette, Baron Solemacher, Mara des Bois
Small, intensely flavoured berries with naturally high Brix. Alpine strawberries need minimal feeding — the concentrated flavour is partly a result of low nutrient availability. Overfeed and you lose the intensity. Mara des Bois is technically a day-neutral but grows like an alpine — treat as alpine for feeding.
Containers vs beds
Containers, hanging baskets & strawberry planters
- Excellent for strawberries — keeps fruit clean, off the ground, away from slugs
- Limited volume means nutrients leach faster — biochar and clay minerals help
- Water daily in warm weather, twice in heatwaves — consistent moisture is critical
- Feed every 4 weeks at the lower end of the range
- Replace compost annually — strawberries deplete container mixes rapidly
- Hanging baskets are ideal for trailing varieties and small spaces
Beds, raised beds & allotments
- Larger soil volume buffers nutrients and moisture better
- Plant through weed-suppressing membrane or mulch heavily with straw
- Water deeply 2–3 times per week rather than little and often
- Runners root naturally — manage or remove depending on your system
- Rotate every 3–4 years to prevent soil-borne disease build-up
- Net against birds as fruit colours — or lose 50% of your crop
Runner management
Runner production diverts energy from fruit. For maximum berry quality, remove runners as they appear throughout the fruiting season. To propagate new plants, allow 3–4 runners per mother plant after harvest, peg into small pots of compost, sever once rooted (4–6 weeks), and plant out in autumn. Replace strawberry plants every 3–4 years — cropping quality declines after the third season.
Ideal soil pH
Strawberries prefer slightly acidic soil at pH 5.5–6.5 (ideally around 6.2). Test annually. To lower pH: elemental sulphur at 100–200g/m² (takes 3–6 months). To raise pH: agricultural lime at 100–300g/m² (takes 3–12 months). Incorporate 3–12 months before planting. The calcium from Gypsum in this formula does not raise pH.
UK seasonal timeline
| Month | What to Do |
|---|---|
| Feb–Mar | Clean up dead foliage from overwinter. First feed as new growth appears (100–170g/m² or 15–40g per plant). Mulch with straw once soil warms. Net against birds. |
| April | Flowering begins. Protect from late frosts with fleece overnight. Keep soil moist. Remove runners on established plants. |
| May | Second feed for June-bearers (80–160g/m of row). Fruit setting. Tuck straw under developing fruit to keep clean. Continue removing runners. |
| June | Main harvest for June-bearers. Pick daily. Feed everbearing and day-neutral varieties every 4 weeks at the lower end. |
| July | Post-harvest feed for June-bearers — critical for next year. Second and third flushes for everbearing types. Allow selected runners to root for propagation. |
| August | Final feed for everbearing varieties. Sever rooted runners and pot up or plant out. Stop feeding June-bearers by late August. |
| Sep–Oct | Plant new bare-root runners. Last fruits from everbearing types. Remove old straw mulch. Tidy beds. |
| Nov–Jan | Plants dormant. No feeding. Protect containers from hard frost. Plan next season's replacements (replace after 3–4 years). |
Common problems
Botrytis (grey mould)
The most common strawberry disease in the UK. Good air circulation, straw mulch to keep fruit off soil, and prompt removal of infected berries are the primary controls. EM-1 and chitin from Mealworm Frass in this formula build the competitive microbial community that suppresses Botrytis. Avoid overhead watering during fruiting.
Powdery mildew
White powdery coating on leaves, curling and purpling. Silica Meal in this formula strengthens leaf cell walls — a physical barrier against spore germination. Ensure adequate spacing and air flow. Foliar seaweed extract improves plant resistance.
Vine weevil
No fertiliser controls vine weevil directly. Biological control: apply nematodes (Steinernema kraussei) in spring and autumn. Check compost for C-shaped white grubs when repotting. Container-grown strawberries are most at risk.
Slugs
Straw mulch lifts fruit off the soil surface. Organic slug pellets around the bed perimeter. Containers and raised beds reduce slug access. Pick fruit daily as it ripens — slugs target overripe berries first.
Bird damage
Net the entire bed or row as soon as fruit begins to colour. Use fine mesh (2cm or less). Support netting above the plants — not draped directly on foliage. Without netting, expect to lose 30–50% of your crop.
Red stele (red core)
Wilting despite moist soil, red-stained root cores when cut open. No cure — remove and destroy affected plants. Improve drainage. Do not replant strawberries in the same soil. Choose resistant varieties (Hapil, Florence, Rhapsody). Good drainage is the single most important preventive measure.
The science of strawberry flavour and why nutrition is decisive
Strawberry flavour is the result of three interacting systems: sugars (primarily fructose and glucose for sweetness), organic acids (citric acid for the characteristic tang), and volatile organic compounds — over 360 identified VOCs, of which approximately 15–25 are sensorially important. The balance between these three determines whether a strawberry tastes flat or complex.
Why K-led nutrition for strawberries
Potassium is the primary driver of phloem loading — the transport of sucrose from leaves into developing fruit. Under K deficiency, berries are lower in Brix, lower in volatile esters, and measurably less sweet. The 3-2-7 ratio delivers a K:N of 2.4:1 — high enough for K to dominate sugar transport and ester biosynthesis while N remains sufficient for healthy foliage.
Key aroma compounds
| Compound | Sensory Character | Nutritional Link |
|---|---|---|
| Furaneol (DMHF) | Caramel, sweet, "strawberry" | The defining strawberry aroma; production increases under K-rich organic nutrition |
| Methyl butyrate | Fruity, apple, pineapple | Ester biosynthesis depends on K supply and enzyme cofactors (Zn, Fe) |
| Hexyl acetate | Pear, fruity, floral | One of the most abundant esters; enhanced by organic management |
| Linalool | Floral, citrus, sweet | Terpene produced more abundantly in biologically active soil |
| γ-Decalactone | Peach, creamy | Lactone from lipid precursors; requires adequate lipid metabolism cofactors |
Mechanisms of action
Potassium drives sugar and ester production
K activates sucrose synthase and drives phloem loading into developing fruit. Higher Brix, higher fructose, and increased substrate availability for ester biosynthesis — the volatile fruity compounds that define strawberry aroma.
Low nitrogen preserves flavour intensity
Excess N produces large, watery berries with diluted sugars, suppressed volatile production and higher nitrate. The moderate 3% N through slow organic mineralisation prevents this — plants receive what they need without the excess that degrades quality.
Calcium for firmness and shelf life
Calcium cross-links pectin in cell walls. Adequate Ca supply produces firmer berries that resist bruising and deterioration 15–25% longer than Ca-deficient fruit. 7.2% from four sources at different speeds ensures continuous supply to developing berries.
Anthocyanin biosynthesis
High K and sulphur from Yorkshire Polyhalite stimulate the phenylpropanoid pathway — the biosynthetic route to anthocyanins, the red pigments that are also potent antioxidants. Deeper red colour correlates directly with higher antioxidant content and consumer preference.
Microbial metabolites and flavour
Decomposing organic ingredients generate secondary metabolites that enter the plant and directly influence volatile biosynthesis. Organic management consistently produces strawberries with higher total VOC content and more complex aroma profiles.
Disease suppression through biology
Botrytis is the primary quality-limiting disease. EM-1 Microorganisms and chitin from Mealworm Frass build competitive microbial communities that suppress Botrytis through competitive exclusion — reducing grey mould incidence without fungicide.
Study data
| Study | Finding |
|---|---|
| Organic fertilisation trials (2020–2025) | Low-N, high-K organic systems: sugars/Brix +15–45%, aroma volatiles (esters) significantly enhanced vs high-N alternatives. |
| Biofertiliser combination trials (2023–2024) | Organic NPK + biologicals: higher sugars, phenols, anthocyanins, antioxidant activity. High-K systems outperformed balanced or high-N for sweetness and aroma. |
| Global meta-analysis (2023) | Combined NPK + organic: nutritional quality +12–30%. Strawberries identified as highly responsive to organic nutrition quality benefits. |
| Calcium and strawberry firmness | Adequate Ca supply improved berry firmness by 15–25% and extended shelf life. Multiple sources at different speeds outperformed single-source application. |
| Humic acid and strawberry Brix | 15–30% higher Brix and sugar content in humic acid-treated trials. Enhanced antioxidant and flavour compound production. |
References
- Marschner, P. ed. (2012). Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press.
- Wang, Y. et al. (2023). Combined organic–mineral fertilisation meta-analysis. Science of the Total Environment.
- Nardi, S. et al. (2009). Physiological effects of humic substances. Soil Biology and Biochemistry.
- Khan, A.A. et al. (2009). Triacontanol. Plant Growth Regulation, 53(3), 203–218.
- Craigie, J.S. (2011). Seaweed extract stimuli. J. Applied Phycology, 23(3), 371–393.
- Lehmann, J. et al. (2011). Biochar effects on soil biota. Soil Biology and Biochemistry, 43(9), 1812–1836.
- Johnston, A.E. & Dawson, C.J. (2018). Polyhalite as a fertiliser. Proc. 826, Int. Fertiliser Society.
- Epstein, E. (1999). Silicon. Annual Review of Plant Physiology, 50, 641–664.
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