Can I use the Helix calculator's schedule directly for an auto?

The calculator is calibrated for 13-week photoperiod strains. Use it to find the reference dose for your substrate and week, then apply the 1/4-1/2 factor for autoflowers. There's no separate 'auto mode' because exact doses depend on the genetics and size of each variety.

What week does an autoflower start flowering?

It depends on genetics, but most modern varieties show first pistils between weeks 3 and 4. You don't change the light schedule — the plant decides on its own. That's why it's important to have all 3 bases active from the first weeks, even at low doses.

Is CALMAG worth adding in soil with an auto?

In soil that's already well-amended with calcium, CALMAG may not be necessary in the early weeks. It does make sense to add it from flower onset if you see symptoms on new growth — marginal chlorosis or curling tips are usually the first sign of calcium deficiency. In coco, on the other hand, CALMAG starts from day 1.

Do autoflowers handle alkaline water the same as photoperiods?

Same rules apply to any cannabis: irrigation pH needs to be in range (hydro 5.6-5.8, coco 5.8-6.2, soil 6.0-6.5). With unadjusted alkaline water, iron precipitates out regardless of plant type. ALPHA and GAMMA both carry EDDHA-chelated iron, which stays stable between pH 4 and 10 — but you should still adjust pH after mixing your solution.

Does the light schedule matter for autoflowers?

Flowering is automatic and independent of the light schedule, but more hours of light means more photosynthesis and more energy available to the plant. Most indoor growers run 18/6 or 20/4 for the entire cycle. Dropping to 12/12 at flower, the way you would with a photoperiod strain, has no advantage in an auto and only reduces photosynthetic output.

Autoflower Nutrients: Dosing, Cycle, and the 3-Base System

Why does an autoflower burn at a normal feeding dose?

Autoflowers (Cannabis ruderalis crosses) are genetically smaller, with a proportionally reduced root system and an accelerated development rate. The result is that the ratio between the amount of nutrients reaching the root zone and the plant biomass that can actually process them is far less forgiving than in a large photoperiod variety. The same solution concentration a 90-day photoperiod plant handles without a hitch can cause nutrient toxicity — tip burn, calcium and magnesium lockout — in a 60-day auto.

The principle is simple: less plant, less root mass, less buffer. Any excess accumulates faster and there's less time to correct it before harvest.

How much do you reduce the dose compared to a photoperiod strain?

The widely accepted field rule is to start at 1/4 to 1/2 of your photoperiod reference dose for the same substrate. That range isn't arbitrary — it reflects both the smaller plant size and the metabolic sensitivity that comes with ruderalis genetics. In practice:

Seedling and early veg (weeks 1-3): start at the low end of the range, around 25% of the photoperiod reference dose for your substrate.
As the plant shows healthy leaves and active growth, you can gradually increase — no rush — up to a maximum of 50% of the photoperiod reference dose.
If you see tip burn, yellowing on new growth, or leaf curl, back off immediately: the short cycle gives you no time to recover from a serious toxicity.
Photoperiod reference doses by substrate and week are available at /calculators/dose. Calculate the reference dose for your substrate and week, then apply the reduction factor based on how your plant responds.

What does an autoflower cycle look like, and what changes about feeding?

A typical autoflower cycle runs ~8-10 weeks from germination to harvest, versus the 13-18 weeks of a standard indoor photoperiod. The stages are all there — just compressed:

Weeks 1-2: seedling and root development. Relatively high demand for calcium and phosphorus for root establishment. Very low doses of all 3 bases.
Weeks 3-4: brief veg. The plant grows actively and by week 3-4 can already show first pistils — the flip is automatic, no light schedule change needed.
Weeks 5-7: active flowering. Potassium and magnesium demand rises alongside bud development. BETA takes a larger share of the ratio during this phase.
Weeks 8-10: ripening and flush. Nutrient demand drops. Many growers do a short 3-5 day flush in plain pH-adjusted water before harvest.

The critical point is that with an auto there's no '12/12 transition week' and no long veg period to correct mistakes. The plant enters flower when its genetics decide. If it arrived at flowering under-fed, yields will suffer. If it arrived with excess nutrients, that stress compounds at the moment of peak demand.

Do all 3 bases run together, or do you split them by stage?

ALPHA, BETA, and GAMMA run together the entire cycle — even in autoflowers. What changes between stages is the relative ratio of each base, not whether any of them is present or absent.

ALPHA provides nitrate nitrogen and base calcium. Cannabis science confirms that optimal N during veg sits in the 160-200 ppm range (Saloner & Bernstein 2020, Kpai et al. 2024); in an auto that range applies proportionally to the reduced overall concentration.
BETA delivers bloom phosphorus and potassium. Studies by Westmoreland & Bugbee (2022) and Hershkowitz et al. (2025) show optimal P for cannabis is between 15-60 ppm — pushing higher provides no benefit, and in the limited substrate of an auto, less is more.
GAMMA supplies micronutrients, EDDHA-chelated iron, and root support. In autoflowers it's especially important in the first few weeks while the root system is getting established.

What role do CALMAG and CANDY play in an autoflower run?

CALMAG matters most in coco, where the coir fiber competes with calcium and magnesium uptake. Optimal magnesium for cannabis sits at 35-70 ppm (Morad & Bernstein 2023, Volcani Center) and calcium at 100-160 ppm (Llewellyn et al. 2023, Guelph). In a coco auto, a Ca or Mg deficiency takes hold fast and there's no time to fix it: running CALMAG from week 1 in that substrate is a preventive practice, not an optional add-on. In soil and hydro the dose is lower.

CANDY (carbohydrates) feeds the substrate microbiome and is relevant in soil and coco, where a microbial community exists. In autos the use pattern is the same as in photoperiods — skip the first few weeks, introduce it in late veg/flower on alternating waterings, and cut it during the flush. The difference is that the window of use is shorter because of the compressed cycle.

What's the recommended starting point for feeding an auto?

The Essential Kit (ALPHA + BETA + GAMMA) is the right entry point. It covers everything an autoflower needs to complete a healthy cycle without the complexity of juggling multiple additives across an 8-10 week run.

Start all 3 bases at 25% of the photoperiod reference dose for your substrate (calculated at /calculators/dose).
Keep pH dialed in: hydro 5.6-5.8, coco 5.8-6.2, soil 6.0-6.5. In autoflowers, pH out of range is just as limiting as excess nutrients.
Watch the new growth: if the first 2-3 sets of fan leaves come in green and develop normally, you can start nudging the dose up gradually.
Add CALMAG from day 1 if you're growing in coco. In soil and hydro, evaluate based on leaf color and turgor.

What mistakes most commonly ruin an autoflower grow?

Starting at the same dose as a photoperiod: it's the most common mistake and the hardest to recover from in a short cycle.
Transplanting late or stressing the plant during veg: autos don't have time to bounce back from a rough transplant in week 2-3. Many growers germinate directly into the final container.
Poor pH control: in a compressed cycle, pH out of range for 3-4 days can lock out nutrients at exactly the moment peak flowering demand hits.
Dropping one of the bases because 'it's flower time': all 3 bases run together, always. Cut ALPHA during early flower and you lose the nitrogen and base calcium the plant is still actively using.
Flushing too long: in an auto, a flush longer than 5-7 days eats a meaningful percentage of the total cycle. Three to five days in plain pH-adjusted water is enough.

Technical information based on a review of the scientific literature on cultivation. It is not medical advice and does not imply in-house trials of the product.