Houseplant fertiliser schedule UK — month-by-month NPK guide

Houseplant fertiliser schedule UK — month-by-month NPK guide

UK houseplant fertilising sits in the gap between "no one tells you, so you skip it for a year" and "online advice says feed weekly and the plant dies of salt burn." Neither is right for a British home. Indoor plants in pots have one cubic foot of compost to draw from for years — without supplemental nutrients they slowly run out of nitrogen, phosphorus and potassium and stop growing. But they also can't escape excess feed, so over-fertilising burns roots faster than dehydration does — and the long UK winter dormancy (October-February) makes salt build-up worse than in warmer climates. This guide is the realistic schedule for British plant parents: when to feed, what NPK ratio actually matters for which plant, which UK brands work, and the salt-flush protocol that prevents 80% of fertiliser accidents.

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NPK basics in 90 seconds

Every fertiliser label has three numbers, e.g. 10-5-5 or 20-20-20. They are the percentage by weight of:

• N — Nitrogen. Drives leaf and stem growth. Houseplants with green showy foliage (monstera, pothos, philodendron, snake plant) want N-leaning feed.
• P — Phosphorus. Drives root development and flowering. Flowering houseplants (peace lily, orchid, anthurium, African violet) benefit from a P boost during bud formation.
• K — Potassium (potash). Drives overall vigour, disease resistance, and water regulation. All plants need it; deficiency shows as yellowing leaf edges. UK gardeners often call this "potash" on product labels.

Balanced ratios (10-10-10, 20-20-20) work for almost every common UK houseplant. Specialty ratios matter mostly for orchids (10-30-20 during bud set), cacti (low-N, around 2-7-7) and African violets (matched even ratios with extra micronutrients). RHS guidance is consistent: most foliage houseplants do well on a balanced general feed at half-strength.

The month-by-month UK schedule

Default for foliage houseplants in a British home:

Key rules:

1. Half-strength always. Manufacturer labels are written for outdoor garden plants in full British summer sun. Indoor plants need roughly half what the label says, full stop. If the label says 10 ml per 4.5 litres of water, use 5 ml.
2. No feed on dry compost. Always water first or feed with the watering — fertiliser salts on dry roots cause chemical burn. The 30-minute rule: water 30 minutes before feeding, or mix the fertiliser into the watering can directly.
3. No feed for 6 weeks after buying. UK nurseries (Patch Plants, Beards & Daisies, Hortology, Grow Tropicals) pre-load growing media with slow-release fertiliser (Osmocote or equivalent). Adding more liquid feed in the first 6 weeks pushes you into burn territory before the slow-release runs out.
4. No feed for 4-6 weeks after repotting. Fresh peat-free compost (Westland or Sylvagrow) already contains starter charge. Wait until that's depleted.
5. No feed if the plant is sick. Fertiliser is not medicine. A wilting, root-rotted or pest-infested British plant needs the root cause fixed first; feeding stressed plants kills them faster.

For species that flower indoors (orchid, peace lily, anthurium), switch to a "bloom booster" or to Levington Tomorite (4-3-8, high in potash) for 2-3 feedings during bud formation, then return to balanced. For cacti and succulents, feed only April-September at quarter-strength using a specialist cactus formula.

UK fertiliser brands — what actually works

Brand names matter because they're what readers buy. All brands below verified available in 2026 via UK garden centres and Amazon UK.

The four UK staples

• Westland Houseplant Feed (concentrate, around 5-3-3) — liquid concentrate, sold at B&Q, Wickes, Dobbies, Notcutts, Squires, garden centres and Amazon UK. Reliable mid-range default for foliage houseplants. Typically £5-7 for 200 ml.
• Baby Bio Original (10.6-4.4-1.7) — the iconic British houseplant feed, liquid concentrate, sold at ASDA, B&M, garden centres and Amazon UK. Small 175 ml bottle lasts a year. High nitrogen leaning — best for foliage species (monstera, pothos, philodendron). Tradition more than science, but it works.
• Phostrogen All Purpose Plant Food (14-10-27 with trace elements) — soluble powder, sold by Bayer Garden / SBM Life Science across UK garden centres and Amazon UK. High-potash, good for flowering and fruiting plants as well as foliage. Has been on UK shelves for 60+ years. Mix a teaspoon per 4.5 litres of water.
• Levington Tomorite (4-3-8) — primarily marketed for tomatoes, but RHS notes it works well for flowering houseplants when bud formation is the goal. Liquid concentrate, sold absolutely everywhere — Tesco, Sainsbury's, B&Q, Wickes, every UK garden centre, Amazon UK. £4-6 for 1 litre. Don't use on foliage-only species (too low in nitrogen).

Other reliable UK options

• Empathy After Plant Houseplant Food — RHS-endorsed organic-leaning feed, made in the UK. Sold at RHS Plants, Crocus and online.
• Maxicrop Original Seaweed Extract — gentle seaweed-based liquid, builds resilience over time, sold at most British garden centres.
• Doff All Purpose Soluble Plant Feed — budget option, widely available at British supermarkets and garden centres.
• Vitax Houseplant Feed — UK manufacturer, sold at Wickes and independent garden centres.
• Osmocote Plus Indoor & Outdoor Smart-Release — slow-release pellets that feed for 6 months. Sprinkle in spring, forget about it. Good for British plant parents who travel.

The brand matters less than the routine — any balanced fertiliser used consistently at half-strength outperforms any premium product used erratically.

Plant-specific UK patterns

Rough groupings, by demand level:

Heavy feeders — monthly during UK growing season

• Monstera deliciosa, pothos, philodendron (vining and self-heading), tradescantia, fiddle-leaf fig, rubber plant, schefflera, croton
• Use Baby Bio Original or Westland Houseplant Feed at half-strength March-September
• See monstera care UK, pothos care UK and fiddle-leaf fig care UK

Moderate feeders — every 6-8 weeks during growing season

• Calathea, peace lily, spider plant, dracaena, aglaonema, ZZ plant, prayer plant
• Westland Houseplant Feed at quarter-strength is the safe default for fussy calatheas
• See calathea care UK, peace lily care UK and spider plant care UK

Light feeders — every 8-12 weeks, quarter-strength

• Snake plant, cast iron plant, jade plant, aloe, most succulents, most cacti
• Use a specialist cacti and succulent feed (Westland or Doff) at quarter-strength only
• See snake plant care UK, aloe vera care UK and jade plant care UK

Specialty feeders — bloom booster during bud set

• Orchid (Phalaenopsis especially), anthurium, African violet, hoya
• Switch to Levington Tomorite or a specialist orchid feed (high P or balanced potash-leaning) for 2-3 feedings as buds appear
• See orchid care UK

Salt build-up and the UK flush protocol

Every liquid fertiliser leaves mineral salts in the compost. Over months, these accumulate and damage roots — the visible symptom is a white or yellow crust on the compost surface or around the pot rim, plus increasing crispy leaf tips even though humidity and watering are correct. UK hard-water tap supply (most of southern and eastern England) makes this worse because limescale adds to the salt load.

Flush twice a year (March and August):

1. Move the pot to a sink, bath or outdoors.
2. Run room-temperature water (rainwater if your area has hard tap water — Kent, Essex, Cambridgeshire, London) slowly through the pot. Let it drain.
3. Repeat 3-4 times. You're aiming for water roughly 3-4 times the pot volume passing through.
4. Let drain completely. Empty any standing water in the saucer.
5. Skip the next scheduled feeding — the compost is depleted; give it 2 weeks to recover.

If the compost surface has a visible white salt crust, scrape off the top 1 cm and replace with fresh peat-free compost before flushing.

For severe build-up (the plant has been over-fed for a year), repot completely into fresh mix — see how to repot a plant UK and use our pot size calculator to confirm the new pot size.

Organic vs synthetic — when it matters in UK homes

For indoor pots, the differences are smaller than gardening media imply:

• Synthetic (Phostrogen, Baby Bio, Westland) — fast-acting, predictable NPK ratios, cheap, easy to over-apply. Best for new British growers who follow a schedule.
• Organic (Empathy, Maxicrop seaweed, fish emulsion, worm castings) — slower-acting, builds compost microbiome over time, gentler — harder to burn plants even at recommended strength. Slight smell on fresh application (fish emulsion especially).

Most UK indoor plants do fine with either. If you compost at home or care about soil microbiology, organic is the better fit. If you want clear numbers and consistent results, synthetic is fine. Switching between them is also fine — plants don't care about your worldview.

Common UK fertilising mistakes

1. Feeding in winter. Plants are dormant — UK daylight is too short for the plant to use the nutrients. Excess feed in low-light British winter conditions accumulates as salt because the plant can't absorb it. Pause November-February without exception.
2. Feeding at full label strength. UK fertiliser labels are written for outdoor garden plants. Indoor plants need half. Quarter for cacti and succulents.
3. Feeding newly-bought plants immediately. British nursery growing media is pre-loaded with slow-release feed. Wait 6 weeks after purchase from Patch Plants, Beards & Daisies, IKEA UK or B&Q.
4. Feeding on dry compost. Burns roots. Always water first, or mix into the watering can.
5. Feeding a stressed plant. A plant with root rot, pest infestation or transplant shock cannot use the nutrients and they accumulate as salt. Fix the underlying issue first — see why is my plant dying UK.
6. Skipping the flush. Two years of monthly liquid feed without a flush guarantees salt damage, especially in hard-water UK regions. Twice a year takes 10 minutes per plant.
7. Using Tomorite on foliage-only plants. Tomorite's 4-3-8 ratio is low in nitrogen — your monstera will yellow over time. Use it only on flowering or fruiting species, and even then only during bud set.

Related articles

• Indoor plant care UK — the broader British care hub
• How to repot a plant UK — when feeding isn't enough
• Humidity for houseplants UK — companion seasonal-care guide
• Brown spots on plant leaves UK — diagnose over-feeding
• Yellow plant leaves UK — diagnose nutrient deficiency
• Why is my plant dying UK — Pillar 1 diagnostic when feeding goes wrong
• Pot size calculator — match the pot to the plant
• UK hardiness zones — match plants to your region

NPK guidance cross-referenced with RHS Fertilisers: Types and Uses. UK brand availability verified May 2026 across B&Q, Wickes, Dobbies, Notcutts, Squires Garden Centres, Amazon UK and Tesco. Reviewed and updated by the Growli editorial team.