Updated: Nov 15, 2019
Efficiencies of Light and Space
Outdoors plants may be free to roam and stretch but when faced with a small indoor growing area efficiencies of space and maximum use of the available light on offer become a vital part of a production system. Obviously when artificial light is supplied, a grower will want to make use of every photon produced and some planting designs are more efficient at this than others. Where crop plants of a similar size are being grown in a hydroponic system, under artificial lighting, the most efficient use of lumen levels produced is where each plant is a equal distance from the light source. This is generally not obtained where the plants are all sitting in a flat layer – some plants will be directly under the light source(s) while others at the edges of the ‘table’ are further away and therefore receive light of a lower intensity. This type of arrangement doesn’t make the most efficient use of valuable light energy and can result in uneven growth and development.
Most lamps have an efficient reflector above the bulb which acts to reflect light waves back down into the plants, rather than having them directed upwards and wasted. These reflectors however diffuse light back downwards on a fairly wide angle, rather than directly downwards which could cause hot spots and burning of the foliage. Since this reflection is at a wide angle, it makes sense to position plants not only directly below the bulb, but also to the sides to prevent ‘light waste’ a common problem in badly designed indoor grow rooms.
Since it is ideal to have all plants placed an equal distance from the light source, optimum use of the available light (both reflected and direct lumens) is obtained when the planting system is designed to produce a ‘stadium’ effect. This means when the newly planted system with small plants is set up, the light(s) can be lowered into the center of the ‘stadium’ so that each plant is an equal distance from the light source. As the plants grow upwards, lights have the potential to be raised with the crop while still keeping the same stadium effect. A semi-tiered or stadium type planting, also means more gullies and more plants can be grown in the same floor area and more use is made of the vertical space available. In an area which would only hold 6 channels if these are played in a single flat layer, the stadium type systems can hold 12 of the same size channels.
Another factor which concerns growers producing plants under lights is plant size – if the plant gets too tall before it’s fully mature it can simply run out of room for development. Smaller plants are better suited to systems which have limited developmental space and they also make better use of light. Many crop plants from tomatoes to wheat to flowering ornamentals and herbs have been specifically bred for ‘compact growth habits’ which mean a greater yield can be obtained from the same unit of area. Many plants are even treated with growth regulators to ensure they remain as short and compact as possible while under cultivation. The reasons for choosing a short compact plant over a tall one are many – firstly shorter plants have a greater ability for self support and resistance to ‘lodging’ or stem breakage’s when insufficient support is a problem. Shorter, smaller plants will usually have the same number of nodes on the stem as a much taller plant of the same species and even the same number of leaves, so vegetative yield is not affected. Shorter internode area, which reduce plant height, do not affect or reduce yields, since yield is determined by assimilate production, flowering ability and general plant health, not the length of the stem internode area.
With shorter and smaller plants, more plants can be grown in the same area as a lesser number of tall spreading plants of the same variety, so the potential to increase yield is greater. This has been seen with many crops which are now selected for compact growth habits so that planting densities and yields can be pushed higher.
Under artificial lighting where maximum use of all lumen levels produced is important, smaller plants have a huge advantage (apart from not hitting the roof before they are mature). When light levels are originating from a single source overhead, the leaves at the top of the plant tend to be fully saturated with light, however those below the top leaves are receiving ‘second hand light’, that is light that has passed through the top canopy of leaves down to the lower layers of the plant. The greater the depth of the canopy, the lower the light levels reaching the leaves for photosynthesis A shallow canopy has greater light penetration and radiation levels at its lowest levels than a tall, deep canopy where light intensity falls off drastically towards the base of the plant. Tall plants which only have their top few layers of leaves receiving sufficient light tend to naturally stretch upwards anyway complicating the low light problem down below even further. Leaves on the lower stems of tall plants which don’t receive sufficient light are a drain on the plant – they can not produce sufficient assimilate to keep the leaf active and functioning and it will soon age, turn yellow and begin to die back. Leaves which are in shade and dying back due to insufficient light are a magnet to plant pathogens who prefer to attack those areas of the plant which are weakened in some way.
The other factor to take into account when considering plant size is not just the upper portion of the plant but also the root system. Smaller plants generally have much smaller root systems than larger plants and smaller root systems use less dissolved oxygen than a larger root system with a greater surface area. Since oxygen is vital for plant growth, and large, overcrowded root systems from large plants will deplete oxygen levels rapidly under warm conditions, smaller plants in a hydroponics system makes a lot of sense. Where root overcrowding causes nutrient stagnation and suffocation in hydroponic systems where too many large plants have been forced to grow, opportunist root pathogens will rapidly attack the weakened root system, causing major problems.
High yielding, small, compact plants are the ideal way to produce hydroponic crops in just about every situation and system. Since making maximum use of very photon produced by artificial lighting becomes vital in confined growing spaces, compact plants in stadium type arrangement equal distance from a highly efficient lamp design will give optimum performance from a grow room system.