Getting started.

How long a cycle lasts, from sowing to harvest

A very simple question, and yet one never asked in this course until now: when exactly do you harvest. Tomatoes, chillies and sweet peppers don't complete their cycle at the same pace, but they go through the same milestones: sowing, emergence, transplanting, first flower, fruit set (the fertilisation that turns a flower into a fruit), then harvest.

🍅 Tomato: 5 to 8 days from seed to emergence, at a substrate temperature of 24 to 29 °C (species-by-species detail in the Sowing & cuttings step). Transplanting into a pot comes at the first or second set of true leaves, roughly 3 to 4 weeks after sowing; the final move into the finishing pot follows around 6 weeks after sowing (rule of thumb, carried over from open-field growing, to be adjusted indoors). Once the flower has set, the fruit reaches the "mature green" stage, already harvestable, in 35 to 42 days; it takes 45 to 60 days after flowering for a fully red tomato. Adding up these markers, and allowing a few weeks of growth before the very first flower, take away an order of magnitude of 3 to 4 months between sowing and your first ripe tomato (rule of thumb, adding up the sourced milestones above). On a determinate variety, the harvest then concentrates into 3 to 5 weeks and the plant stops on its own; on an indeterminate one, it spreads out continuously for as long as you keep growing the plant (see below, "Choosing the variety").

🌶️ Chilli and sweet pepper (same family, Capsicum): emergence in around 8 days at a substrate temperature of 25 to 30 °C, and transplanting that follows the same rhythm as the tomato (rule of thumb, for lack of separate data for these two crops). After that, they diverge a little. Chillies take 35 to 45 days between flowering and full colour, with a heat peak around 40 to 50 days after flowering on hot varieties (rule of thumb). Sweet peppers offer the most solid marker on this whole page: 75 to 80 days from transplanting to harvest (Oklahoma State Extension), with full colour taking up to 80 to 85 days depending on the variety. In both cases, expect an order of magnitude comparable to the tomato: 3 to 4 months.

Remember the order of magnitude, not day-level precision: 3 to 4 months between sowing and your first harvest, for all three crops. Drying chillies adds still more time on top (detail in the Harvest & drying step). This isn't a sprint, it's what you're preparing for right from this step, tent and light included.

Measure your space, then choose your tent

Three measurements before anything else

Allow 160 to 200 cm of height for the tent depending on the format, plus the heat and noise of the extraction. Choose a room where it can live without getting in the way.

From a closet to pro formats: it all exists

The four formats for a first cycle

From 100 × 100 cm upwards, these tents rise to ≈ 200 cm tall most of the time (220 to 240 cm on the large formats).

The forgotten criterion: height

Where the 160 cm of a starter tent go

The result: a shorter tent becomes viable.

🍅 Tents 120 to 150 cm tall are first-time growers' regret n°1: once the pot is in place and the lamp hung, there's no room left to raise the light as the tomato grows. Plan for height in reserve, or a training approach that limits plant size: that's exactly what the next section is about.

Three ranges at GrowLED

Choosing the variety, before you buy

One word hasn't appeared yet in this step, and yet everything above depends on it directly: the variety. Before buying seeds or seedlings, decide between determinate and indeterminate. Tomatoes, chillies and sweet peppers all exist in both families.

A determinate variety stops by itself at a fixed height, roughly 1.2 to 1.5 m, once its terminal bud has formed (Univ. of Vermont Extension, Univ. of New Hampshire Extension). Its flowers cluster together, its harvest concentrates into 3 to 5 weeks and then the plant stops producing. It needs little pruning: on a determinate variety, you never remove the suckers — each one carries its own harvest (the full detail is waiting for you in the Staking & upkeep step).

An indeterminate variety never stops by itself: it keeps growing and flowering continuously for as long as you grow it, until you stop it yourself (topping, pruning the apex) or you end the cycle. It's the one that produces the longest, but it's also the one that poses a very concrete problem inside a tent: you've just worked out a usable height of roughly 90 to 100 cm in a tent 160 cm tall. An untrained indeterminate outgrows that volume within a few weeks of active growth:

Open the illustration full size

How to choose, depending on your tent format: in a compact tent (60 × 60 or 80 × 80 cm, the most limited usable height), go for a determinate variety or a compact cherry-type variety, easier to fit without heavy training. In a taller tent (120 × 120 × 200 cm and above), an indeterminate is still workable, provided you plan the training from the start: topping, staking, stripping the lower leaves — all of that is handled in the Staking & upkeep step, but the decision itself is made now, before you buy.

Light: power follows surface area

Three markers are enough: the watts actually drawn at the socket, the area covered, and the distance to the top of the plants. The scaling rule fits in one sentence: power follows surface area.

• 60 × 60 cm → ≈ 100 W of recent LED
• 80 × 80 cm → ≈ 200 W
• 100 × 100 cm → ≈ 300 W
• 120 × 120 cm → ≈ 465 to 620 W

The sizing rule itself is counted per square metre: aim for 320 to 430 W/m² at full fruiting, in other words 30 to 40 real watts per square foot (rule of thumb, detailed in the Lighting step).

These power levels cover the hungriest phase, fruiting, which requires, in lighting terms alone, 400 to 500 µmol/m²/s of PPFD (the flux of photons usable for photosynthesis) over 16 h, i.e. a DLI of 23 to 29 mol/m²/day, where a seedling needs far less, on the order of 100 to 440 depending on its stage, the dose rising as it emerges (the full progression, stage by stage, is detailed in the Sowing & cuttings step). The complete calculation of PPFD, DLI and spectrum is developed in the Lighting step. Hence the old hands' reflex: a dimmable lamp slightly oversized, set to 25 to 50 % for seedlings, then opened up gradually.

On duration, the tomato tolerates 14 to 18 h of light a day in growth and in fruiting, and in practice the timer gets set to 16 to 18 h; the sweet pepper tolerates longer days. Beyond 18 h, the tomato gains nothing more, it only gets stressed (leaves yellowing between the veins). Remember the "1 % rule", validated on tomato and sweet pepper:

Plan for the bill: real watts × hours. A 200 W LED running 16 h draws ≈ 3.2 kWh a day. All of it gets reused cycle after cycle: an investment, not a consumable.

Want your answer straight away, without redoing the calculation yourself? Enter your tent format, or its dimensions if you're outside the standards, to get your LED power, your recommended extraction and your indicative plant count directly.

The minimum kit: the essentials first

Six items are enough; everything else is level 2. Here's the essential, with the role of each element:

• The tent: a controlled volume, reflective and light-tight.
• The dimmable LED: sized to the surface area, as seen above.
• The extractor fan + carbon filter: the extractor renews the air (fresh CO₂ for the plants, heat and humidity out); the carbon filter traps odours before the air leaves.
• The circulation fan: it stirs the air inside the tent and strengthens the stems, but it brings in no fresh air and does not replace extraction.
• The thermo-hygrometer: your two daily control figures.
• The timer socket: automated day/night cycles, without having to think about it.

Conversely, the maximum we recommend without reservation is 900 W (SpectraWILD L900) on 120 × 120 cm: beyond high intensities you need CO₂ supplementation, otherwise it's like having a Ferrari with no clutch. That's a commercial limit of our range, not a measured growing benchmark: the 465 to 620 W bracket seen above already covers all of fruiting without added CO₂. Don't hesitate to ask us for help if you need it.

To size the extraction, our calculator works from the volume of your tent, not from the power of your LED: the two have nothing to do with each other (we'll come back to this below). Here are the values it produces:

Air comes in at the bottom, leaves at the top, and the walls should be drawn slightly inwards: the signature of a tent under slight negative pressure, where nothing leaks. The carbon filter alone costs ≈ 25 % of the airflow, hence extractors recommended above the calculated need. The filter itself is chosen to the extractor's nominal airflow, in the upper part of the recommended bracket (rule of thumb): an undersized filter throttles the whole circuit, whatever the fan. The complete sizing logic, the intake, air circulation and day-to-day climate control are detailed in the Ventilation & climate step.

Field tip: run the extractor at reduced speed — less noise and some margin for summer. Without air renewal, makeshift setups literally "cook" the plants:

Optional, later on: a smart controller that drives the extractor according to temperature and humidity (level 2), a humidifier if your room is very dry, CO₂ enrichment, which only makes sense once light and climate are under control. Same discipline on inputs: one to three products to start with, fewer variables, easier diagnosis. For the substrate, choose a light potting mix, little or not pre-fertilised: the "long-lasting enriched" mixes sold for general gardening cause uncontrollable overdoses.

Climate targets, phase by phase

Two figures drive everything: temperature and relative humidity (RH). Look at them morning and evening — that's the whole basic routine.

At sowing, heat does everything, and it's the substrate temperature that rules, not the room's: aim for 24 to 29 °C in the heart of the root ball, for tomatoes as much as for chillies and sweet peppers, with the probe pushed into the compost (species-by-species detail in the Sowing & cuttings step). After emergence, come back down to around 21 to 24 °C by day and 16 to 18 °C at night until transplanting (rule of thumb):

🌶️ Chinense-type chillies (habanero and company) germinate hotter still than the annuums: a heat mat under the seed tray changes everything. And watch the night temperature with Capsicum: chillies and sweet peppers want 18 to 21 °C at night, where the tomato is happy with 17 to 18 °C. Below 15 °C or above 32 °C, their flowers drop and fruit set fails.

In production, aim for 21 to 27 °C by day and 17 to 18 °C at night for the tomato; for chillies and sweet peppers, 21 to 26 °C by day and 18 to 21 °C at night. Below 16 °C, the tomato absorbs phosphorus poorly and its foliage turns purple. That's a warning signal, nothing irreversible: bring the temperature back up.

On humidity: the tomato tolerates 60 to 85 % RH with an optimum at 60 to 70 %; chillies and sweet peppers do well between 65 and 85 %. Flowering is where everything is decided: pollination is optimal around 70 % RH; above 80 %, the pollen clumps; below 60 %, the stigma dries out and the flower aborts.

🍅 Above 30 °C, lycopene no longer forms: the tomatoes stay orange instead of turning red. In high summer, it's properly sized extraction, and its speed margin, that saves the colour of the harvest. Full control of ventilation, VPD and day-to-day decision-making is waiting for you in the Ventilation & climate step.

Starting up in the right order

The order matters as much as the equipment. Here's the sequence that avoids most of the disappointments:

1. Assemble the tent in its final place, within reach of the socket.
2. Install the extraction at the top with its carbon filter, the ducting directed out of the tent, and the air intake open at the bottom.
3. Hang the lamp high, you'll lower it as growth goes on: at full intensity, the top of the plants sits 30 to 40 cm from the LEDs (a starting point, to be adjusted to the measured PPFD, as seen in the Lighting step).
4. Wire it up cleanly: power strip fixed up high, no cable on the floor near water, timer set to 12 to 14 h of light while you're still at the seedling stage, 16 to 18 h once the plants are transplanted.
5. Run it empty for 24 h (rule of thumb) and check that temperature and humidity stay within the targets. Only then do you bring your plants in.

The point beginners discover too late:

Lamp and extractor hang above a volume where you water: fix all the hardware securely, check that cables and sockets can take the load, and leave no connection within reach of splashing water.

The 24 h running empty are not wasted time: it's the only moment to set extraction, fan and dimmer without risking "cooking" a seedling. If the tent gets too hot when empty, it'll get hotter still with plants transpiring: fix it now, not in ten days.

The first week: what to expect

Here's what a well-run first week looks like.

On light: lamp high, 45 to 75 cm above the seedlings depending on its power (rule of thumb), and dimmed to 25 to 50 %. A seedling can only take, depending on its stage, 100 to 440 µmol/m²/s, the dose rising as it emerges (progression detailed in the Sowing & cuttings step):

On watering, get ready to fight your best instinct. We've all done it: watering "to do the right thing", and drowning the seedling with love. Over-watering is the most widespread killer of seedlings. The old hands' rule: water generously, then wait for the compost to dry at the surface (finger test, first knuckle) before the next watering. A seedling would rather be a little thirsty than have its feet in water.

On mindset, remember the formula: "control the environment, listen to the plants". Stabilise temperature, humidity and light, then let them get on with it: by constantly checking, moving and adjusting, the beginner creates their own problems. Also measure the pH of the water running into the saucer after watering: an off pH mimics a deficiency, and you'd be adding fertiliser when the problem lies elsewhere.

🌶️ Chillies need more heat at start-up than tomatoes, up to 29 to 32 °C of substrate for the chinense types (rule of thumb), hence the heat mat. As long as the climate stays within the targets, a seedling that takes its time is not a failed seedling.

In summary, here are the correspondences that structure everything else: surface area, plants, light and extraction.

Beyond 120 × 120 cm (150 × 150, 200 × 200, 240 × 240, 300 × 300, 600 × 300 cm and up), the logic doesn't change: power follows surface area and extraction follows volume. Tell us about your project, we'll size it with you.

Plants: rules of thumb, varying with pots and training, see above. Airflow: values from the GrowLED calculator with a carbon filter; when in doubt, take the next diameter up.

Equipment checklist

• 80 × 80 cm grow tent: 0.64 m², the compact format that lights and climate-controls itself effortlessly, for a complete first cycle.
• Dimmable LED grow light ≈ 200 W: power follows surface area, and the dimmer covers seedlings at 25 to 50 %.
• Extractor fan + carbon filter kit: renews the air and traps odours before they leave; sized with the GrowLED table (180 to 250 m³/h for 80 × 80 cm).
• Circulation fan: stirs the air and strengthens the stems, alongside the extraction.
• Thermo-hygrometer: your two control figures, morning and evening.
• Timer socket: 16 to 18 h of light a day in growth and in fruiting, automated.
• Light, lightly pre-fertilised potting mix: you manage the feeding yourself, with no surprise overdose.
• Easy-release pots: a root ball handled gently at repotting means roots that get going again without stress.