💡  Tip burn is an environmental nutrient disorder that appears in the later weeks of the production cycle, between weeks 5-6. Tip burn occurs when there is a calcium deficiency at the edges of the inner leaves due to the plant’s growth ability to outpace the calcium transport.

📌 Tip-burn Symptoms:
▶ Brown edges of leaves
▶ Occurs in the first-sprouted inner leaves
▶ Becomes visible around the 5th week, affecting marketability

🎯 Dr. Chieri Kubota at Ohio State University researched mitigation strategies to avoid tip burn with her main focus being: Is there a difference in profitability between an early harvest and a full-cycle production?

The benefits of growing indoors are becoming more and more recognized as technology and research in the industry continue to advance. One of those benefits, rapid plant growth, might come with a few draw backs that could affect the health and marketability of the crop. One of those concerns is tip burn, otherwise known as a calcium deficiency.

Why Does Tip Burn Appear?

The inner leaves of a crop, let’s say lettuce, tend to sprout from the seedling first, with the outer leaves, sometimes called the wrapper, growing later in the production cycle. Indoor grow operations and greenhouses create optimal growing conditions for the plants, manifesting in accelerated growth and harvest times. Due to this accelerated growth cycle, the leaves of the crop can grow too quickly for the calcium to reach the growing tissue of the inner leaves. Calcium generally flows where higher levels of transpiration occurs, namely the outer leaves.

Dr. Kubota highlighted 5 reasons why tip burn can be problematic in indoor vertical growing operations.

Why Does Indoor Growing Risk Tip Burn? 

Optimal Growing Conditions

Proper indoor grow operations are referred to as environmentally controlled agriculture, with the elements of the climate manipulated to create optimum conditions for plant growth. Due to this, crops grow and are harvested much more rapidly than outdoor growing.

Airflow 

The head of lettuce is enclosed by leaves that block air movement around the growing tip and create a very humid micro-environment, resulting in low transpiration and a decreased flow of calcium. According to Dr. Kubota, indoor plants receive less than 0.1 meter/second of airflow around the plants. 

High Daytime Relative Humidity 

Low humidity increases transpiration and promote calcium uptake. It is not unusual, according to Dr. Kubota, to see indoor growing humidity greater than 70%.  

Net Radiation 

Total radiation of sunlight spectrum. The lighting over a crop is more intense outside under the sun which has more energy than electric lighting. Electric lighting doesn’t encourage as much transpiration as natural sunlight.

Harvesting Early

As a way to avoid tip burn, Dr. Kubota researched harvesting crops early, around the 4th week of the production cycle. However, harvesting early reduces the crop size. Therefore, higher planting density is needed to compensate for the decreased size. Since most farmers package leaves and not heads, the price point should not be affected. Early harvest increases the likelihood for aesthetically-pleasing produce.

Conclusions

In her research, Dr. Kubota found that short-cycle production avoided tip burn with a decrease in annual yield relative to full-cycle production. However, short-cycle production requires higher density planting in order to match the annual yield of full-cycle production.

There is a draw-back to high density, short-cycle production growing: Overhead. Additional space is needed for higher-density planting, as well as a cost increase in labor and seeds. The short-cycle crops also had a shorter shelf-life which poses as a risk to marketability and profitability.

  Watch Dr. Kubota’s full presentation