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Feeding · 8 minute read · Updated October 15, 2026

Cannabis feeding schedule basics

A feed chart is a starting point, not a prescription. Your plant only asks for enough, and research on cannabis keeps finding that enough is less than many growers pour.

The real cost of feeding by the bottle

Nutrient labels often show a full-strength rate that is more than many plants can use, especially young ones. New growers follow it, the leaf tips burn, and they assume they need a different product.

Look at what controlled studies found:

• A 2025 Utah State University study doubled nutrient strength from EC 2 to EC 4 in hydroponics. Yield and cannabinoid levels did not significantly change.
• A 2021 University of Guelph study on flowering cannabis found the best nitrogen rate was about 194 mg/L, and yield did not respond to potassium across the range they tested. The authors noted that the 300 to 400 mg/L potassium some commercial growers use is likely too high.

So here is a question worth sitting with: is your plant asking for more food, or are you reading that from a chart? The schedule below starts low and lets the plant pull you up.

What the plant uses at each stage

Fertilizer bags list three numbers, N-P-K: nitrogen, phosphorus and potassium.

• Nitrogen (N) builds leaves and stems. Veg plants need the most.
• Phosphorus (P) supports roots, energy and flowers.
• Potassium (K) runs water movement and overall plant health.

The classic rule: high nitrogen in veg, then less nitrogen and more phosphorus and potassium in flower. The direction is reasonable, but the research says the swing is smaller than bloom-booster labels suggest. In a 2020 study from Israel's Volcani Center, vegetative cannabis did best at 160 mg/L nitrogen; at 30 mg/L it showed clear deficiency, and above 160 extra nitrogen started to hold growth back. In flower, the Guelph study put the best phosphorus rate at about 59 mg/L, and the Utah State study found just 15 mg/L phosphorus was enough in hydroponics. Plants in flower still need plenty of nitrogen: the Guelph optimum for flower, 194 mg/L, was not lower than the veg optimum, and the Guelph paper cites the Israeli team's work as putting about 160 mg/L as best for both stages. Cutting nitrogen hard at the flip is not what the research supports.

Calcium and magnesium matter too, especially in coco and with reverse osmosis water. Many growers add a cal-mag product for that reason.

A simple starting schedule

Use this as a frame, then let the plant adjust it. Strength is shown as a share of the label's full rate and as EC for coco and hydro.

Autoflowers follow the same order on a shorter clock, and many growers keep them a little lighter. For the pH to pair with each stage and the ppm conversions, see the pH and PPM chart.

Soil, coco and hydro feed differently

The same schedule plays out very differently depending on what the roots sit in. Not sure which one you have? Our guide to soil, coco or hydro in a tent compares them.

• Bagged potting soil with fertilizer added. Many bags carry enough food for the first few weeks. Feeding on top of that early is a common cause of burn. Start feeding when the lower leaves begin to pale, and many soil growers feed every second or third watering rather than every time.
• Amended or living soil. The food comes from organic matter that soil life breaks down. You mostly water, and top-dress when needed. See living soil basics.
• Coco coir. Coco holds almost no food. Feed a light solution with nearly every watering, add calcium and magnesium, and aim for some runoff each time.
• Hydro. You control everything, and mistakes show fast. Check EC and pH daily.

A note on organic liquid feeds: earlier Guelph trials with an organic liquid fertilizer, cited in the 2021 study, got the best yields at higher nitrogen rates, about 390 mg/L in veg and 260 mg/L in flower. The likely reason is that not all organic nitrogen is available to the plant right away. Do not compare an organic label rate directly with a mineral one.

Read the plant, then adjust

The schedule is the plan. The leaves are the feedback. Look at new growth and the lowest leaves every couple of days.

Change one thing at a time and give it several days. Leaves that are already damaged will not turn green again, so judge the new growth.

Feeding mistakes that look like deficiencies

• Feeding a bone-dry pot. University of Tennessee Extension notes that a dried-out mix tests high in salts and can damage roots, and that adding more fertilizer to it is harmful as well as wasteful. Water lightly first, then feed at the next watering.
• Answering every yellow leaf with more food. If pH has drifted, the food is already there and the plant cannot take it up. Check pH before you add anything.
• Feeding seedlings like adults. Small roots in a rich mix burn easily. Quarter strength or plain water is enough for the first weeks.
• Ignoring what your water already carries. Tap water with an EC of 0.4 counts toward your total. Measure it once so your targets mean something.
• Adding several new products at once. If the plant reacts, you will not know which one did it. Add one change at a time.
• Switching nutrient lines mid grow. Strengths and ratios differ between brands. If you must switch, drop back to half strength and build up again.

Do you need to flush before harvest?

Many grow guides say to feed plain water for the last one to two weeks to "clean" the buds. The research so far does not support a benefit.

A Utah State University study found that cutting off nutrients before harvest did not improve flower quality or total cannabinoid yield. Leaves showed deficiency signs within a week, yet nitrogen levels in the flowers did not change. In other words, the plant pulled from its leaves, and the buds stayed about the same.

Where the books and the science differ, we go with the science. A short taper in the final weeks is fine if you prefer it, and the late-season leaf fade is normal. But a long, hard flush is not a proven way to improve your harvest. If salts have built up in the pot, steady runoff through the grow handles that better.

How to mix a feed the right way

1. Start with the water volume you need, at room temperature.
2. Add each nutrient part separately and stir between them. With multi-part lines, follow the maker's order; General Hydroponics, for example, says to add its Micro part to the water first. Never mix concentrates together undiluted.
3. Add cal-mag or supplements as the label directs.
4. Measure EC and compare with your target.
5. Adjust pH last, because the nutrients change it.
6. Water slowly, aiming for some runoff in coco and soilless mixes. See how often to water.

Write down the strength, the EC, the pH and the date every time. A single feed log answers most questions when something goes wrong two weeks later. Canna GLAP logs feeds and waterings per plant in a private, encrypted journal, and you can ask Cannie, the built-in grow assistant, about a leaf by sending a photo.

Questions growers ask

Read next

• Cannabis pH and PPM chart by stage
• Soil, coco or hydro in a grow tent: which should you choose?
• Living soil and no-till: the basics for indoor growers
• Cannabis grow week by week: the full indoor timeline

Education only, for adults 21+ where home cultivation is legal. Updated October 15, 2026.