Farming Guides
How to Grow Cannabis from Seed: Complete Guide 2026
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Editor’s note: This guide is updated every season. Each section links to more detailed articles — use it as a guide to all the information on the 00 Seeds blog.
Table of contents
- Choosing your seeds
- Germination
- Indoor growing
- Outdoor cultivation in Spain
- Advanced techniques
- Nutrition and irrigation
- Common problems
- Harvesting and curing
Growing cannabis from seed is one of the most rewarding experiences a plant lover can have. It can also be frustrating if you start without a clear roadmap. This guide is here to give you exactly that: a comprehensive overview of the process, from choosing the seed to storing the cured buds in a glass jar.
This isn’t an article to read in one go. It’s a guide. Each section gives you the essential information and links you to articles where we explore each topic in much greater depth. Bookmark it and come back whenever you need to.
1. Choosing your seeds: the most important decision
Every crop begins with the choice of seed. And this is where you can make or break an entire harvest before you’ve even planted a single seed. The market offers three main formats, each with its own advantages and ideal grower profile.
Autoflowering seeds
They flower on their own, without being dependent on the photoperiod. You don’t need to change the light cycle; they complete their cycle in 60–80 days from germination and are perfect for novice growers or anyone who wants several harvests a year. The downside: there is less scope for aggressive training techniques, and the yield per plant is lower than that of feminised strains.
→ See all the Autoflowering seeds from 00 Seeds
Feminised seeds
They produce only female plants (those that produce buds). They are the standard choice for controlled indoor grows and for outdoor growing when you want to maximise yield. They require a switch to a 12/12 photoperiod to induce flowering indoors, and rely on natural light cycles outdoors.
→ See all the feminised seeds from 00 Seeds
Fast Version
An improved version of the classic feminised strains: they retain the potency and yield of photoperiod strains but reduce the flowering time by 1–3 weeks. Ideal for outdoor growing in climates where autumn arrives early.
→ View special collections
📖 Related article: Automatic vs Feminised vs Fast Seeds: Which one to choose in 2026?
2. Germination: from seed to seedling
A cannabis seed that has been stored correctly has a germination rate of over 90 %. The problem is almost never with the seed itself: it lies with the method or the conditions.
The kitchen roll method (the most reliable)
- Moisten two sheets of kitchen paper with settled tap water (without active chlorine).
- Place the seeds between the sheets of paper, inside a covered dish.
- Keep it between 22 and 26 °C. You’ll see the radicle within 24–72 hours.
- Repot when the root tip is 1–2 cm long, taking care not to touch it.
Temperature and humidity during germination
The optimum temperature is between 22–26 °C. Below 18 °C, the process slows down or stops. The ambient humidity must be high (70–80 %) for the first few days. A cheap plastic propagator works perfectly for this.
First transplant
Once the seedling’s first pair of cotyledons are fully open, it is ready for its first permanent repotting (or into a 0.5-litre pot if you are going to carry out several stages of repotting). Use a light, well-aerated growing medium with a low nutrient content.
3. Indoor growing: total control of the environment
Growing indoors means you have complete control over everything: light, temperature, humidity, CO₂, and nutrients. That’s a huge advantage, but it’s also a responsibility. A mistake with any of these parameters will cost you in terms of yield or quality.
Lighting
Light is the most critical factor in indoor growing. There are three main options:
- Full-spectrum LED: The current standard. Low energy consumption, minimal heat build-up, and excellent canopy penetration if you choose a high-quality model. For a space measuring 1.2×1.2 m, you’ll need between 400–600W of actual power.
- HPS/HID: Tried and tested over decades. It generates a lot of heat (requires a powerful extraction system) but the yields are very consistent. It is being used less and less in new set-ups.
- CMH/LEC: A good mid-range option, with a spectrum similar to that of natural sunlight.
The light cycle for the vegetative phase is 18 hours of light / 6 hours of darkness. To induce flowering in feminised plants, switch to a 12/12 cycle. Autoflowers are generally kept on an 18/6 or even a 20/4 cycle throughout their entire growth cycle.
Growing medium and containers
For novice growers, soil is the most forgiving growing medium. Choose a cannabis-specific mix with good water retention but also good drainage (20–30 % of perlite is the most common addition). The size of the container determines the final size of the plant: 11–15 L for autoflowering strains, 15–25 L for feminised strains grown indoors.
Temperature and humidity
Ideal range during the vegetative stage: 22–28 °C with 50–70 % relative humidity. During flowering, gradually reduce humidity to 40–50 % to prevent mould. The temperature may drop by 5–8 °C overnight: in some strains, this brings out purple hues.
Ventilation and extraction
You need at least one extractor fan to refresh the air in your space every 1–3 minutes. Add a carbon filter if odour is a problem. Internal air circulation (a couple of small fans) strengthens the stems and prevents hotspots of humidity.
4. Outdoor growing in Spain: the Mediterranean sun working in your favour
Spain has one of the best climates in the world for growing cannabis outdoors. The Mediterranean sun, particularly in the Levantine region, produces crops of the very highest quality with energy costs close to zero.
Crop calendar for the Iberian Peninsula
| Month | Activity |
|---|---|
| February–March | Indoor germination (using artificial light) |
| April–May | Outdoor transplanting (temperate zones), start of the growing season |
| June–August | Lush vegetation, training techniques |
| September–October | Flowering, monitoring for fungal diseases |
| October–November | Harvest (depending on variety and region) |
Growing plants on terraces and balconies
Growing on a balcony is perfectly feasible with the right strains. Look for compact strains (autoflowering or feminised, low-growing Indica), use large pots (at least 20–30 litres) and make sure you have good drainage. In summer, you may need to water twice a day if the pot gets very hot.
Recommended varieties for outdoor growing in Spain
- Automatic: short growing cycle, ideal for two harvests in the same season.
- Feminised Indica or Indica-dominant strains: better heat tolerance and a lower risk of botrytis during flowering.
5. Advanced techniques for increasing production
Once you’ve got the basics under your belt, training techniques are the next logical step. The aim of all of them is the same: to help the plant distribute its energy more effectively and ensure that light reaches more flowering points.
SOG — Sea of Green
Lots of small plants in a small space, with a very short vegetative phase. Instead of growing one large plant, you plant 9–16 plants per square metre and switch them to the flowering stage when they are 20–30 cm tall. The result: more frequent harvests and a very high total yield per square metre.
📖 A comprehensive guide to the SOG method
SCROG — Screen of Green
A horizontal net (usually 40–60 cm above the growing medium) along which the branches are trained during the vegetative growth stage. The aim is to create a uniform canopy where all flowering points receive the same amount of light. It requires a longer growing season, but yields are higher than with any other indoor technique.
LST — Low Stress Training
Bend and secure the branches with cable ties or soft wire whilst the plant is growing, without cutting them. This transforms the natural apical structure (a cone) into a flat structure with multiple flowering points at the same level. It works particularly well with autoflowers, which do not tolerate high-tension techniques very well.
Topping and FIM
Cut the apical meristem (topping) or the 80 % of the apical bud (FIM) to force the plant to develop two or more main branches instead of one. This is combined with LST to produce very broad and productive plants.
Defoliation
Prune leaves strategically to improve light penetration and air circulation. This is a controversial technique: if done incorrectly, it can put the plant under too much stress. Only use this method during the vegetative stage or in the first two weeks of flowering.
6. Nutrition and watering: no more, no less
Over-fertilisation (giving too many nutrients) is the most common mistake made by novice growers. The plant shows symptoms of nutrient burn, so the grower assumes it is lacking something and adds more. The result is a toxic growing medium and a plant that cannot absorb anything.
Macronutrients by phase
- Vegetation: High nitrogen (N), moderate phosphorus and potassium. NPK ratio 3-1-2.
- Early flowering: Reduce nitrogen, increase phosphorus. NPK 1-3-2.
- Advanced flowering: Minimum nitrogen, maximum potassium. NPK 0-3-3.
- Last two weeks: Rinse with clean water to remove any salt residue.
pH: the overlooked factor
Cannabis absorbs nutrients within a very specific pH range: 6.0–7.0 in soil, 5.5–6.5 in hydro/coconut fibre. Outside this range, the nutrients are present in the growing medium but the plant cannot take them up. This results in deficiencies that cannot be corrected, no matter how many nutrients you add. Always measure the pH of your irrigation water.
Watering frequency
The basic rule: water when the growing medium is dry to a depth of 2–3 cm. Over-watering is the second most common cause of problems after pH. Roots need oxygen: a constantly damp growing medium suffocates them and opens the door to pathogens.
7. Common problems: identifying them and taking prompt action
Every experienced grower has lost at least one plant. The difference between a good grower and a mediocre one isn’t about avoiding problems: it’s about spotting them in time and responding correctly.
The most common nutritional deficiencies
- Nitrogen deficiency: Progressive yellowing of the lower leaves, spreading upwards towards the upper leaves. Most commonly seen during the late stages of flowering (natural) or due to an inappropriate pH.
- Deficiencia de calcio: Manchas marrones en hojas, puntas quemadas. Común en cultivos con agua blanda o pH bajo.
- Deficiencia de magnesio: Amarillamiento entre las venas de hojas medias. Se corrige con sulfato de magnesio (sal epsom).
Plagas habituales
- Spider mite (araña roja): Puntitos blancos en el envés de las hojas, telarañas finas. Se desarrolla con calor y baja humedad. Tratamiento: aceite de neem, jabón potásico, predadores naturales.
- Fungus gnats (mosquito de la tierra): Las larvas atacan las raíces. Control: dejar secar bien el sustrato entre riegos, arena gruesa en la superficie.
- Trips: Líneas plateadas en las hojas. Tratamiento: spinosad, piretrinas naturales.
Enfermedades fúngicas
- Botrytis (moho gris): El enemigo número uno en floración. Se desarrolla con alta humedad y poca circulación de aire. Elimina partes afectadas inmediatamente y mejora la ventilación.
- Oídio (mildiu polvoroso): Polvo blanco en las hojas. Prevención: buena circulación de aire, humedad controlada. Tratamiento: bicarbonato de sodio, azufre mojable.
📖 Related article: Marihuana adulterada vs natural: cómo detectarla
8. Cosecha, secado y curado: donde nace la calidad final
Muchos cultivadores dedican meses a cuidar sus plantas y luego se precipitan en la cosecha. Es el error más caro del proceso: una cosecha demasiado temprana o un secado mal hecho destruye semanas de trabajo.
¿Cuándo cosechar? Leer los tricomas
La forma más precisa de determinar el punto óptimo de cosecha es observar los tricomas con una lupa de 30–60x o un microscopio de mano:
- Tricomas transparentes/cristalinos: Demasiado pronto. La planta sigue produciendo cannabinoides.
- Tricomas lechosos/blancos: Punto óptimo para efecto más cerebral y energético.
- Tricomas ámbar: THC degradándose en CBN. Efecto más corporal y sedante. Cosecha entre el 10–30 % ámbar según preferencia.
El color de los pistilos (pelos del cogollo) es una referencia visual más fácil pero menos precisa: cuando el 70–90 % han oscurecido y se han retraído, suele ser momento de cosechar.
Secado
Corta las ramas principales y cuélgalas en una habitación oscura, con temperatura de 18–22 °C y humedad del 45–55 %. La circulación de aire debe ser suave (no apuntes ventiladores directamente a los cogollos). El proceso dura 7–14 días. El cogollo está listo cuando la ramita interna cruje al doblarla, pero el exterior sigue siendo ligeramente flexible.
Curado
El curado es la diferencia entre cogollos que huelen bien y cogollos que saben excepcional. Coloca los cogollos en tarros de cristal herméticos, llenos al 70–80 % de su capacidad. Durante las primeras dos semanas, abre los tarros 1–2 veces al día durante 10–15 minutos (proceso llamado «burping»). Después, una vez a la semana durante 4–8 semanas más.
El curado correcto mejora el sabor, suaviza el humo, estabiliza la potencia y permite almacenar durante meses sin perder calidad.
Variedades de 00 Seeds recomendadas según perfil de cultivo
La elección de la variedad correcta para tu situación concreta puede suponer la diferencia entre una cosecha mediocre y una excepcional. Aquí tienes una selección comentada según diferentes perfiles:
Para cultivadores que empiezan
- Automatic en general: ciclo fijo, sin gestión de fotoperiodo, rápidas. → Ver automáticas
Para maximizar producción en interior
- Gorilla Glue — producción masiva de resina, 26–28 % THC, ideal para SOG o SCROG.
- Gelato — terpenos premium, calidad de dispensario californiano, 24–26 % THC.
- Para exterior en España
- Feminizadas índica-dominantes con floración antes de mediados de octubre.
- Apple Bananas — perfil exótico, disponible en versión automática y feminizada.
Para efecto equilibrado
- Blue Dream — equilibrio sativa/índica, 20–22 % THC, disponible en Fast Version.
→ Ver el ranking completo: Top 6 Variedades de 00 Seeds para 2026
→ Catálogo completo de semillas 00 Seeds
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