Feeding autoflowers is a bit like fuelling a race car that never stops for a pit stop. Once they are off the line, they go straight through to the finish. Anything you give them - too much, too little, too early or too late - has an impact. There is no pause, no extra lap, and no chance to backtrack if things go sideways.
Unlike photoperiod plants, autos follow their own internal timer. Light cycles don’t matter (well, not as much). By the end of week five, most will have started flowering, whether you are ready or not. And with just 11 to 12 weeks from seed to harvest, every decision counts.
This guide lays out what to feed, when to feed it, and how to avoid overdoing it. We will look at nutrient ratios, pH levels, a week-by-week schedule, and why holding back often gets better results than pushing too hard.
Essential Nutrients for Autoflowering Cannabis
Autoflowers don’t follow the same rules as photoperiod plants and they don’t all follow the same rules as each other either. Some can handle full-strength nutrients without blinking. Others will sulk at half-strength and start clawing their leaves in protest.
The trick is knowing your strain and starting gently. Always do strain-specific research—read grow diaries, watch a few YouTube runs, and look for feeding charts that match your medium and setup. What works for a lanky sativa auto could overwhelm a compact indica with the same mix.
Even better, keep your own journal for every strain and every grow. Note what you fed, when you fed it, and how the plant responded. Over time, those notes will be more valuable than any bottle label.
Macronutrients: NPK Ratios
NPK stands for nitrogen, phosphorus, and potassium - the three main macronutrients cannabis needs to grow, flower, and stay healthy. Most autoflowers follow the same general pattern:
- Early growth (weeks 2 to 3): more nitrogen to build structure
- Pre-flower (weeks 4 to 5): a balanced feed with a bit more strength
- Flowering (weeks 6 to 8): less nitrogen, more phosphorus and potassium
Late flower (weeks 9 to 11): minimal nutrients or just water
A rough guide looks like this:
- Veg: 4-2-3 to 10-5-5
- Flower: 5-10-10 to 0-3-3
But this isn’t a fixed formula. Some autos, especially larger or more robust strains, can handle feeding levels near photoperiod by week four or five. Smaller strains often need a lighter touch from start to finish.
Start with 25 to 50 percent of what the bottle recommends and let the plant show you what it needs. Dark green, shiny leaves with burnt tips mean too much. Pale or slow growth might mean too little. Somewhere in the middle is where you want to be.
Micronutrients: Supporting Plant Health
Micronutrients don't get much attention until something goes wrong. Then suddenly everyone’s talking about rust spots and twisted leaves. Calcium, magnesium, sulfur, iron, zinc, and boron may only be needed in small amounts, but they’re essential for healthy growth, especially in fast-moving autoflowers.
Coco and hydro growers should pay close attention here.
Coco coir has a “high cation exchange capacity” which means it tends to bind calcium and magnesium. Even when pre-buffered, it can still draw those elements away from your plant unless you supplement. Hydro systems offer no buffering at all - your plant only gets what you give it. If you’re using reverse osmosis (RO) water, you're starting with a clean slate that lacks both calcium and magnesium from the start.
Because of that, most growers using coco, hydro, RO water, or LED lighting will need to supplement with Cal-Mag at some point. Not during germination or seedling stage, but once the first true leaves are out and the plant begins to photosynthesize in earnest you may need to - but again, this is slightly strain dependent.
LED lights also increase the plant’s metabolic rate, which tends to push magnesium demand up. It’s not a huge difference, but it can add up across the grow.
Keep an eye out for early deficiency signs - interveinal yellowing, rusty spots on older leaves, curling or blotchy discoloration. If you’re feeding correctly and your pH is in range, micronutrients are the next place to look.
How the Size of Autoflowers Impacts Nutrient Requirements
Autoflowers tend to be smaller than photoperiod plants, both above and below ground. That smaller root zone and shorter veg time mean they simply don’t need as much food to get going. Feed too heavily, especially in the early weeks, and you risk stunting growth just when it should be accelerating.
That said, not all autos are small. Some strains - especially modern hybrids - can get fairly chunky and tolerate moderate to high feed levels once they are established. Others stay small and prefer minimal feeding throughout the grow.
Start every grow with a light touch. Let the plant tell you what it wants. If it's pushing out healthy, upright growth with bright green leaves, you’re on track. If it starts to claw, burn, or stall, ease off. With autos, it's much easier to feed a little more than to undo the damage from feeding too much.
Week-by-Week Feeding Schedule for Autoflowers
This schedule is based on a typical 11 to 12-week autoflower grow, with flowering usually beginning at the end of week 5. Adjust slightly based on your strain and medium, but the general principles hold across most setups.
Weeks 0 to 1: Germination and Seedling Stage
- Soil: No feed required. A quality starter mix should carry the plant through.
- Coco/hydro: Optional 10-25% seedling-strength nutrients.
- Focus: Keep moisture and warmth consistent. Do not overwater.
Weeks 2 to 3: Early Vegetative Stage
- Feed: 4-2-3 NPK at 25–50% strength.
- Coco/hydro: Begin gentle Cal-Mag supplement if using LEDs or RO water.
- Watch for: Upright leaf posture, steady new growth, and light green color.
Weeks 4 to 5: Late Vegetative / Pre-Flower
- Feed: Increase to 10-5-5 NPK at 50–75% strength if the plant is thriving.
- This is the last proper veg week. Flowering will begin any day now.
Watch for: Pre-flowers (tiny white pistils), stretching, and increased thirst.
Weeks 6 to 8: Early to Mid-Flowering Stage
- Feed: Switch to bloom feed around 5-10-10 NPK.
- Optional: Low-dose PK booster in week 7 if the plant is strong and hungry.
- Reduce nitrogen to avoid leafy buds or late-flowering delays.
- Watch for: Pistil formation, trichome production, rapid bud development.
Weeks 9 to 11: Late Flower and Flushing
- Feed: Ease off - either reduce nutrients to a minimal bloom formula (0-3-3) or switch to plain water.
- Flush: In soil, you may choose to flush the final 4 to 10 days. In coco, a shorter flush is fine.
- Watch for: Trichomes turning milky with some amber. Buds should swell and slow in development.
Importance of pH Levels in Nutrient Uptake
Even if your nutrient mix is perfect, it won't matter if your pH is off. Incorrect pH levels lead to nutrient lockout, where the plant physically can’t absorb what’s available - even if it’s swimming in it.
Ideal pH ranges:
- Soil: 6.0 to 7.0
- Coco/hydro: 5.5 to 6.5
Always pH your water after adding nutrients. In coco, check your runoff weekly. Drift outside the target range and you’ll start seeing deficiencies, even when you're feeding correctly. A decent digital pH pen is a small price to pay to avoid weeks of troubleshooting.
Organic vs Synthetic Nutrients: Pros and Cons
There’s no right or wrong answer here - just what suits your style and setup.
Organic nutrients
- Feed the microbes, not just the plant
- Ideal for soil, especially if you’re reusing your medium
- Slow-release and more forgiving, but harder to tweak mid-grow
Synthetic nutrients
- Precise, fast acting, and easier to control
- Perfect for coco and hydro where you control every input
- Needs careful monitoring to avoid salt buildup or pH swings
Pick the one that suits how you grow. Organic in living soil, synthetic in coco or hydro (just be sure to use coco nutes for coco, and hydro nutes for hydro). Keep it simple.
Avoiding Overfeeding and Nutrient Burn
Overfeeding is the most common beginner mistake when growing an autoflower. The signs are easy to spot; burnt tips, clawing leaves, dark, almost waxy growth. If you’re seeing those signs, your plant is telling you it has more than enough.
To avoid it:
- Start light (25–50% strength)
- Feed less frequently in soil
- Monitor EC or PPM in coco or hydro
- Don’t try to fix slow growth by throwing in more nutrients
If things go sideways, flush gently and back off. Most autos will bounce back if you catch it early.
Avoiding Underfeeding and Nutrient Deficiencies
On the flip side, underfeeding does happen, especially if you’re being cautious. Pale leaves, purple stems, and sluggish growth can all point to a lack of nutrients. The trick is to confirm it’s not a pH issue first - correct that, and many “deficiencies” sort themselves out.
If you’re confident your pH is dialled in:
- Increase feed strength gradually
- Watch for changes within a few days
- Use a balanced base nutrient before adding boosters or extras
Autos don’t need much, but they do need something. The goal is steady, healthy growth - not lush excess or spartan struggle.
Final Thoughts
Autoflowers don’t give you second chances, but they do reward attention to detail. Keep your feed light, your pH on point, and your expectations realistic. Learn the quirks of each strain, keep a record of what worked, and refine your approach every time.
Most importantly - resist the urge to do too much. With autos, less truly is more.
