One of the most common questions we get from hobbyists and commercial growers alike is about inner tip burn and how to combat it. It is characterized by necrosis of the innermost leaf tips and occurs most often several weeks after transplant. The problem is exacerbated when the cultivar has a tightly packed growth pattern, especially lettuces (and sometimes even cabbage too).
This is caused by a calcium deficiency in the fastest growing part of the plant so it would seem to make sense that you need to supplement calcium in the nutrient solution. Unfortunately it is not quite that simple, and here’s why:
Calcium is an immobile nutrient; this means that plants are unable to reallocate it if a deficiency occurs. Nutrients like nitrogen and potassium, on the other hand, are highly mobile. This explains why a general nitrogen deficiency will manifest primarily in the older growth, because the plant pulls it away in order to keep the growing tips as healthy as possible. The main way that plants move immobile nutrients, like calcium, is by cycling water up from the rootzone and then transpiring it into the atmosphere. If atmospheric conditions aren’t balanced transpiration is limited. In hydroponic systems, and especially in indoor environments, conditions are generally optimized for rapid growth. This can be problematic because if one variable is out of range it can quickly cause havoc on crops through something like inner tip burn.
Having really powerful lights might seem like a great way to boost your crops and minimize the time from transplant to harvest but if you have insufficient airflow or VPD (Vapour Pressure Deficit) is too high/low, you’re going to run into problems quickly. A good system is a balanced system. RH (relative humidity),EC/PPM of nutrient solution, NPK ratios, pH levels, VPD, light intensity, airflow, CO₂ … all these variables need to be in harmony to grow healthy crops and not see issues like inner tip burn.
We’re starting a new series of blog posts that will aim to focus on these sorts of topics. If you don’t know how some of the acronyms listed above affect plant growth (or what they stand for!) , or would like to learn about in more detail then YOU are our audience. Let us know if there are specific things you’d like discussed, and check back frequently as we plan to be releasing new topics over the coming months. Some things we’ve got coming up include pest management, plant nutrition, mixing and dosing fertilizers, hydroponic system maintenance, plant tropisms, nutrient deficiencies (don’t worry we’re going to look at inner tip burn in more detail, including how to avoid it) to name just a few. Hope to see you around The Farm.