The Nutrient Feeding Schedule: Week by Week from Seedling to Flush

A nutrient feeding schedule is a week-by-week plan that sets out what to feed an indoor plant — and at what strength — from seedling to the final flush. It layers a base grow-then-bloom feed with Cal-Mag, enzymes, silicon and a bloom booster, raising feed strength (EC) from roughly 0.4–0.8 mS/cm at seedling to a 1.6–2.0 peak in flower, then dropping to near-zero for a plain-water flush at the end.

Most "which nutrients?" questions are really "when, and how much?" questions. This hub ties the whole programme together — one master chart, the reasoning behind each layer, and a deep-dive link for every product family. It is one of three companion capstones, alongside the setup checklist and the beginner shopping list.

Who this guide is for: UK home and hobby growers in soil, coco or hydro who want one clear, evergreen feed schedule from the first true leaves to harvest.

What is a full-cycle feeding schedule, and how do the layers stack?

A feeding schedule is not one bottle but five jobs on different clocks. Build it in layers and it stops feeling complicated:

1. Base feed — your grow-and-bloom backbone, switched from a nitrogen-led "grow" formula to a phosphorus-and-potassium-led "bloom" formula once flowering starts (what N, P and K do is in plant nutrients explained; brand-by-brand in choosing a nutrient line).
2. Cal-Mag — calcium and magnesium, every feed in coco or on RO/soft water, which start with little or none.
3. Enzymes — an additive like Cannazym that keeps the root zone clean, on every watering.
4. Silicon — a beneficial element for stem strength and heat resilience, through veg into early bloom.
5. Bloom booster / PK — a concentrated phosphorus-potassium additive for the flowering stretch, timed to a narrow window and never doubled up.

The two numbers you steer by — pH and EC — come next; get them right and the rest is layering.

The complete week-by-week feeding chart, seedling to flush

Here is the master chart. Weeks are approximate — veg runs as long as you like and flowering varies by variety — so read it as phases, not fixed dates, then print it for the tent. Cal-Mag runs at every feed in coco and on RO/soft water throughout (lighter at seedling, stopped at flush).

Feed strength peaks at 1.6–2.0 mS/cm in mid-to-late bloom, then drops for the flush. Two rules keep it safe: strength rises through the grow, peaks, then falls — never held at maximum to harvest; and additives fit around the base feed, they don't add to it — when a heavy booster goes in, ease the base down so total EC stays in range. A worked brand example is in our FloraMax guide.

When should you start feeding seedlings?

Later than most people think. A seedling in pre-fertilised soil already has one to two weeks of food around its roots, so over-feeding is far more common — and more damaging — than under-feeding. Biobizz's guidance is to start only once the plant is 10–15 cm (4–6 in) tall or has 2–4 true leaves, then build up gently from the bottom of the EC range — roughly 0.4–0.8 mS/cm, a quarter to half of full veg strength. Cuttings and clones follow the same rule (rooting them is covered in our propagation masterclass): a plant will not die from too little feed, but it can die from an overdose.

How does the schedule change for soil, coco or hydro?

The shape — grow, then bloom, then flush — is identical in every medium; what changes is the pH you hold, whether Cal-Mag is mandatory, and how often you water:

Soil is buffered and forgiving; near-inert coco and hydro react instantly to pH, so never run a soil formula in hydro. Full comparison in our soil vs coco vs hydro guide. Rockwool and clay pebbles behave like hydro and need preparing first. In recirculating systems, change the reservoir on a regular schedule rather than topping up for ever; the interval is in reservoir management.

When do pH, EC and Cal-Mag come into the schedule?

Every single feed — these are dials you check each time you mix a tank, not stages you pass. Order matters: mix the base feed, add Cal-Mag, then bring pH into range, because feed and Cal-Mag both shift it on the way in. On hard UK tap water your final EC is the nutrient EC plus the water's own, so measure raw water first. A meter showing ppm is multiplying EC by 500 or 700 depending on its scale (per Bluelab), so steer by EC. The full method — meters, calibration and UK tap versus RO — lives in pH, EC and water quality; shop pH & EC testers here.

Where do enzymes, microbes and silicon fit in?

These are the root-zone layer, each on its own clock:

• Enzymes (e.g. Cannazym) run on every watering — Canna's standard dose is 2.5 ml per litre (1:400). They digest dead root matter.
• Silicon (e.g. Shogun Silicon) runs from veg into early bloom at the label dose, added to the tank first (it raises pH) before you correct pH — for stem strength and heat resilience.
• Beneficial microbes — mycorrhizae and bacteria — go in early at transplant (see pots and transplanting), so they colonise as roots develop; they suit living soil and coco over sterile, high-EC hydro.

One rule the schedule enforces: never mix enzyme or microbe products with hydrogen peroxide or other sterilisers — they kill the biology you paid for. The honest read on which additives earn their place is in root-zone health.

When do bloom boosters and PK enter — and exit?

Later than the light flip, and never two at once. A PK booster is a concentrated phosphorus-and-potassium additive for flowering, from a short mineral burst such as Canna PK 13/14 to gentler low-dose liquids. Run one at a time, count it backwards from harvest rather than forwards from the flip, and ease the base feed down to make EC room. Per-product timing, dosing and EC ceilings are in bloom boosters and PK explained; CO₂ enrichment has its own timing in our CO₂ guide.

What if a feed goes wrong mid-schedule?

Stop and diagnose before you add anything. Most mid-grow "deficiencies" are pH-driven lockouts, not a missing nutrient — the food is in the pot, but the wrong root-zone pH stops the plant taking it up. Yellowing on old, lower leaves points to nitrogen; trouble on fresh top growth to calcium or iron. Check pH first, read runoff EC, and flush only if salts have genuinely built up. The full symptom-to-cause triage is in nutrient deficiencies, lockout and flushing.

FAQ

When should you start feeding seedlings? Wait until the seedling is about 10–15 cm (4–6 in) tall or has 2–4 true leaves, then start at a quarter to half strength — roughly 0.4–0.8 mS/cm. Pre-fertilised soil already feeds it for a week or two, so over-feeding early is the more common mistake.

When do you add bloom boosters (PK) to the schedule? After the plant is established in flower — a low-dose liquid PK from about bloom week 4, or a short, stronger PK burst roughly three weeks before harvest. Run only one PK booster at a time, and ease your base feed down so the total EC stays in range.

How do you flush at the end of a feeding schedule? For the last one to two weeks, water with plain or very lightly fed, pH-corrected water so the feed EC drops toward 0.0–0.4 mS/cm, clearing built-up salts before harvest. It is also the fix for a salt-locked medium mid-grow.

What if your EC is higher than the chart says? Check your water first: on hard UK tap water the reading includes the water's own EC, so measure the raw water and allow for it. If the feed itself is too strong, dilute with plain pH-corrected water or ease the base feed.

Do you need Cal-Mag in coco? Usually, yes. Coco binds calcium and magnesium, so add Cal-Mag at every feed; the same goes for RO or soft water, which start with little or none. In soil on hard tap water you usually do not need it.

Recommended kit and further reading

The core kit, layer by layer:

• Base feed: Nutrients & Boosters — every line in one place, from Canna, BioBizz and Dutch Pro to Plagron and Gold Label; for coco, Canna Coco A&B.
• EC meter: Bluelab Truncheon Nutrient Meter.
• Cal-Mag: Canna CalMag Agent and BioBizz CalMag — every feed in coco and on RO water.
• Root zone: Cannazym enzyme every watering; Shogun Silicon through veg and early bloom.
• Bloom boosters: Buddhas Tree PK 9-18 and House & Garden Shooting Powder; browse the full Additives range.

Most relevant collection: Nutrients & Boosters — the whole schedule begins there.

Related guides: plant nutrients (NPK) · choosing a nutrient line · pH, EC and water quality · root-zone health · bloom boosters and PK · deficiencies and flushing.

Why trust The Grow Superstore

We have been helping UK indoor growers since 2009, online and from our physical store in Peterborough — a hard-water city, so matching feed schedules to real tap water is daily work for us, not theory. The chart above is the advice we give in store for a grower's first full cycle, and it never changes: steer by pH and EC, add one thing at a time, and be modest — it is easier to feed a hungry plant than to rescue an overfed one. Pop in to 6 Wulfric Square, Bretton, PE3 8RF for a free in-store consultation and we will build a schedule around your medium, water and setup.