CEA for cannabis and ornamental flowers – Part II

By Dr Tharindu Weeraratne on April, 6 2023
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Dr Tharindu Weeraratne

FLOWER Field-of-gerbera-flowers-in-a-greenhouse-in-Nieuwerkerk-944818216_5649x3766 (small)

Every crop type grows differently from crop establishment to maturity. Furthermore, as the crop undergoes multiple life cycle stages, growing becomes even more complex due to increasing crop cycle time and crop needs. Even under controlled environment (CE) conditions, growers have challenges achieving high yields, quality and consistency for virtually any crop (microgreens, leafy greens, vine crops, berries to cannabis). Under mono-culture and multi-crop conditions, with different developmental stages, it is vital to understand the local environment that they are in, which we call the “microclimate”. Crops grown in controlled environment agriculture (CEA) could be largely categorized into the following categories.

I will be focusing on each of these crop categories in this 4-part series: 


Single-cycle single harvest crops typically grown as annuals (e.g. cannabis, ornamental flowers) - Part II


Cannabis growers grow some of the most expensive crops. Flower growers, at scale rely heavily on timing of the crop. Suppose if a flower grower misses on-time blooming for Mother’s Day or Valentine’s Day, that’s a huge loss!

Cannabis and most ornamental flowers are grown as annuals. The whole crop is harvested at once – e.g. cannabis flowers, poinsettias and petunias. Depending on the cultivation methodology, several crop cycles of cannabis may be grown in an year. Some other flower crops such as roses or gerberas may be harvested multiple times during the crop cycle. Another common aspect of cannabis and ornamental flowers is that they are typically grown as a single layer in greenhouses, hoop-houses and indoor farms. Indoor cannabis growers grow cannabis in two layers as well depending on how they maintain the crop habit.

Flower growers also use hanging baskets (about a couple of feet below the truss) in greenhouses in addition to crops grown on the floor or tables, a type of a two-layer growing system. Cannabis and ornamental flowers are commonly grown on substrates. For irrigation and fertigation, cannabis growers typically use drip or hand watering; flower growers use automated fertigation using booms or hand watering.

Humboldt County Indoors (owned photos) (small)


Cannabis cultivation at scale is highly involved as it’s still a relatively understudied crop when it comes to growing more than a few plants. Growers use various techniques to grow different “strains” most of which are not fully genetically characterized. These are typically highly expensive operations. There is a common misconception that the plants will grow and yield linearly when added more and more light for example. 

Every plant has their maximum photosynthetic capacity and could typically be damaged by high light even when other environmental conditions and rootzone factors are at optimum. During the initial stages of photosynthesis, plants harvest the energy of instantaneous light (imagine light as packets of energy) and store them in special molecules that later pass that energy to drive sugar synthesis (we call that carbon fixation). However, just like any biological system, the photosynthetic set up of plants could only take light up to a given threshold, and beyond that, light would be damaging to the system.

One example is photobleaching – in cannabis, if flowers/pistils are exposed to damaging levels of instantaneous light, the tips of flowers/pistils may lose their color and appear as bleached. This reduces the quality of the harvest. This fundamental phenomenon highlights why it’s so important to measure every environmental factor in your cannabis facility – from the shoot to root.

Cannabis is typically grown as single plants per container on substrates and requires a lot of plant handling; that means there is a greater chance for plant to plant variation in growth, yield and biochemical consistency if they are not grown under uniform environmental conditions. This applies to a grow room or a greenhouse and a single sensor in the middle of the grow area won’t represent the variations in the climate accurately. A network of sensors at the canopy level that represent the grow area would be very useful in identifying environmental inconsistencies. This allows the growers to tag the plants which were in different microclimates and would help immensely in harvesting. A single plant can skew the chemical profile of the harvested lot.

This also permits the growers to take action to modify control methodology to make the growing area more uniform. Just like at the canopy level, it is equally important to understand what’s happening a few feet above the plants and under the canopy. A good example of this is in-canopy RH level especially at late flower stage. What happens if RH goes beyond the levels that trigger botrytis infection? The problem is, RH can vary highly under canopy, location to location due to variations in plant structure and plant handling (e.g. de-leafing). This becomes a much bigger problem if there are more than one strains in the grow room. These are just a few examples of why it’s super important to measure the environment in 3-D space to better understand the environment, thereby get insights about the crop performance, disease and pest incidence which will save a lot of money for cannabis growers.


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Ornamental flowers are primarily grown in greenhouses from plugs to harvest. Some growers also germinate and raise plugs in germination/growth chambers with lighting. I’ve heard from growers about hot/cold corners in the greenhouse and how they affect young and mature plants in monoculture and multi-cropping. This information usually comes from their feel not necessarily by measurement. Imagine the gradients and variations in the environment if they are measured. These microclimates affect plants silently. I’ve worked with growers in the past and noticed how high summer temperatures, if not controlled, could shrink plug production with uneven plug establishment even in highlight loving pansies in greenhouses.


Multi-location environmental sensing at the plant level is much needed in these situations to adjust the environment accordingly and to place the suitable plants in appropriate locations in the greenhouse. This information is also very useful for plant growth regulator (PGR) applications – for planning and selecting the plants/areas that need PGR applications rather than non-selective sprays. Same applies to controlling pests and diseases.


When another plant layer like hanging baskets are added, it creates additional microclimates as the baskets cut light to certain plants during certain times of the day and affects all other environmental factors as well. Now, not only the environment at the plant level changes, it also affects the greenhouse energy, water and CO2 balance as the hanging baskets are kept much closer to the greenhouse trusses and shade screens. This shows how important is to measure the environment at the hanging basket level to apply necessary changes to the greenhouse environment controls. As I mentioned above, timing and quality is key for ornamental plants. Comprehensive knowledge of the 3-D distribution of the climate is invaluable for the growers to bring the maximum from their crops.

Whether it’s cannabis or ornamental flowers, growers have their own challenges around input costs, labor, regulations, financials, etc. Taking the guesswork out of the growing equation will help them focus on the business. That could only be achieved by measuring the growing operation, inputs, environment, plant, crop handling, and so on. By the way, measuring applies to business as well. Distributed sensing will help growers to discover a lot of unknowns in their grows and enable them to implement new strategies to bring the best of the crop genetics.

The moment growers understand inconsistencies in the environment, they can act on them accordingly to bring the plants affected to max production - little things add up very fast!


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