Leafy greens and herbs in vertical farming

Why leafy greens and herbs suit vertical farms

In a vertical farm every gram of produce is grown with electric light, so the crop has to turn light into saleable weight efficiently. A 2022 review in Agronomy by Van Gerrewey and colleagues concludes that rapid-growing, short crops with a large share of saleable parts, meaning leafy greens, microgreens and herbs, are the ones currently grown to be cost-effective. Researchers at the University of Bologna's vertical farm explain the same idea through harvest index, the edible share of the plant. Lettuce and baby-leaf crops put most of their growth into leaves that are sold, rather than into stems, roots or fruit. They also fit shallow tiers and grow in weeks, so each shelf produces many crops a year.

Lettuce types for vertical farming

Lettuce is the reference crop for indoor farms. The UC Davis Postharvest Center groups the common types into upright romaine or cos, with erect, elongated leaves; butterhead, with soft, cupped leaves; and loose-leaf types such as green leaf and red leaf, which do not form a compact head. Crisphead or iceberg lettuce forms a firm, dense head. Common indoor choices are butterhead, loose-leaf and baby-leaf lettuces, sold as whole heads, living heads with roots, or cut salad mixes. Cornell's hydroponic programme targets a 150 g head; its trials worked with the butterhead cultivar Ostinata, and Cornell researchers documented nutrient deficiencies using the butterhead Flandria. Red-leaf types add colour to mixes.

Cultivar choice matters indoors. Cornell notes that the amount of light lettuce can take before tipburn appears depends on cultivar, spacing and airflow, so trial several cultivars under your own lights before committing. For one cultivar Cornell could only reach 12 mol/m²/day of light without tipburn until it added downward airflow, after which 17 mol/m²/day was possible. Record growth time, head weight and tipburn for each cultivar you trial.

• Butterhead: soft leaves, sold as heads or living lettuce with roots.
• Loose-leaf green and red: harvested as heads or cut for mixes.
• Romaine or cos: upright heads; highly sensitive to ethylene after harvest.
• Baby leaf: dense sowing, harvested young for salad bags.

Lettuce growth cycle and harvest

Cornell's handbook gives a complete schedule for 150 g heads. Seed is sown in a nursery, where seedlings grow for 11 days under 24-hour lighting, starting at 50 µmol/m²/s and rising to 250 µmol/m²/s. Seedlings are then floated on nutrient ponds for 24 days, with one re-spacing on day 21 from 97 to 38 plants per square metre. Harvest is on day 35.

In the ponds, Cornell targets a daily light integral of 17 mol/m²/day, air at 24 °C by day and 19 °C by night, relative humidity between 50% and 70%, and nutrient solution EC about 1.2 mS/cm above the source water at pH 5.8. Downward airflow over the plants is what allows that light level without tipburn. Heads can be sold in clamshells with or without roots, or as bouquets in a bag. Cornell stores packed lettuce at 4 °C. UC Davis recommends near 0 °C and above 95% humidity for romaine and leafy lettuce, with a shelf life of around 21 days at 0 °C for romaine and about 14 days at 5 °C if no ethylene is present.

Spinach in vertical farms

Baby spinach is fast but unforgiving. Cornell's baby spinach handbook germinates seed for 2 days, grows it in ponds for 14 days, and harvests by shearing the whole crop above the media about 16 days after sowing. It is emphatic that growers should not attempt a second cut, because pathogens build up in the solution and can destroy both the current and later crops.

The pathogen is Pythium aphanidermatum, a water mould that rots spinach roots. Cornell writes that if no special precautions are taken, a hydroponic spinach grower will eventually lose an entire crop to it. Its main defence is a chiller that keeps the nutrient solution at 15–20 °C, well below the 25 °C used for lettuce, along with a light level of at least 17 mol/m²/day so the crop finishes quickly. Cornell's spinach set points are otherwise similar to lettuce: EC 1.3 ± 0.1 mS/cm above source water, pH 5.6–6.0 and CO2 at 1,000–1,500 ppm when light is available. Packed spinach is stored at 4 °C.

Kale and other brassica greens

Kale is often grown indoors as baby leaf. In a 2024 study at the University of Bologna's AlmaVFarm, baby kale was sown directly into trays at 1,460 plants per square metre and harvested 21 days after sowing. The farm ran 24 °C by day and 21 °C by night, 65–70% humidity, CO2 at 850 ppm, and LEDs at 215 µmol/m²/s for 16 hours a day. The nutrient solution was kept at EC 2.3 and pH 5.8.

The best light recipe in that trial, a red-to-blue ratio of 5 to 1, gave a modelled yield of 54 kg of fresh leaves per square metre of growing surface a year across 17 cycles, and 57 g of fresh leaves per kWh of lighting energy. At that efficiency, 1 kg of baby kale took about 1,000 ÷ 57 = 17.5 kWh of lighting alone. Other brassica greens such as pak choi, mizuna and rocket are grown in similar ways. Oklahoma State University lists pak choi at EC 1.5–2.0 and pH 7.0 in its general hydroponic chart.

Basil in vertical farms

Basil is one of the most widely grown herbs in indoor farms. In a 2019 University of Bologna trial published in Frontiers in Plant Science, sweet basil was grown at 24 °C, 55–70% humidity and 215 µmol/m²/s of LED light for 16 hours a day, with nutrient solution at EC 1.6 and pH 6.5, and harvested 39 days after sowing. Oklahoma State University's chart gives basil EC 1.0–1.6 and pH 5.5–6.0.

The trial found that a red-to-blue light ratio of about 3 to 1 gave the best balance of yield and energy use for basil. UC Davis lists grey mould (Botrytis) as a common disease of basil, and trimming and cool (but not chilling) storage reduce it. Basil breaks the cold-storage rule that suits other greens. UC Davis states that basil is chilling-sensitive and should be stored above 10 °C. Below that, leaves and growing tips brown, veins bronze, and aroma is lost. Expected shelf life is one to two weeks, depending on water loss. Do not put basil in the same 0–4 °C chiller as lettuce.

Mint in vertical farms

Mint is grown from cuttings rather than seed and regrows after cutting, so one planting can be harvested repeatedly. That suits a vertical farm that wants a steady weekly supply from the same trays, but the plants stay in the system for a long time, so check channels and drains for root build-up. Harvest mint as soft stems. UC Davis notes that most fresh herbs keep best at 0 °C, with an expected shelf life of about three weeks at 0 °C and two weeks at 5 °C. Mint is one of the herbs it lists as very sensitive to ethylene gas, which causes yellowing, stem curvature and leaf drop, so keep it away from ripening fruit in storage and transport.

Coriander in vertical farms

Coriander is harvested as whole young plants. In a 2020 hydroponic study from Brazil, published in the Emirates Journal of Food and Agriculture, seedlings were transplanted into channels 10 days after sowing and harvested 20 and 25 days after transplanting, a total of about 30–35 days from seed. The nutrient solution ran at EC about 2.3 mS/cm and pH 5.7–5.8.

The study also shows the risk of heat in warm climates such as much of India. In the shallowest channels, with 2 cm of solution, the solution temperature exceeded 40 °C in the afternoon in one season, while channels with 3 cm of solution stayed at or below 32 °C. Deeper, shaded or chilled solution is important for coriander in warm rooms. After harvest, UC Davis notes that coriander (cilantro) can remain saleable for up to 21 days in good cold storage, but its aroma declines noticeably after about 10 days. Store near 0 °C with high humidity, and sell within the first week or two where flavour matters.

Growth cycles, storage and shelf life compared

The table combines the published cycle lengths and storage guidance above. Cycle figures come from different systems and climates, so use them as starting points and record your own. Shelf life figures assume prompt cooling, high humidity and no ethylene; produce that sits warm after harvest will not last as long. Where a source did not give a figure, the table says so rather than filling the gap with an estimate.

Harvest and postharvest handling

The quality a farm grows can be lost in an hour after harvest. Cool produce quickly, keep humidity high, and limit handling. UC Davis notes that lettuce, especially romaine, yellows within one or two days at room temperature and that exposure to as little as 1 ppm of ethylene can cause brown spotting on romaine, so keep greens away from ripening fruit and from propane forklifts. Plan cold storage by crop. Most greens and herbs belong near 0 °C with more than 95% humidity. Basil needs a separate space above 10 °C. For Indian deliveries to hotels, restaurants and quick-commerce dark stores, check that the buyer's own storage matches, because basil held in a standard vegetable chiller develops chilling injury.

• Harvest in the cool part of the day and move produce to cold storage within minutes.
• Use lined crates or clamshells to reduce water loss.
• Separate basil from other greens in storage and transport.
• Record harvest date on every pack so buyers can rotate stock.

Growing greens and herbs with Garden & Acre

For homes, cafés and schools that want to grow lettuce, basil, mint and other greens, Garden & Acre's hydroponic and aeroponic towers come installed with the pump, timer, first seedlings, nutrients, training and a refill plan, priced on WhatsApp. The grow light is not included. For commercial or campus farms, our Vertical Farm Setup service plans the crop mix, designs and builds the farm, and supports the first crops, and our Vertical Farm Consulting service helps existing farms with crop planning, troubleshooting and SOPs. Both are priced in a written proposal.

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