Why Are My Lettuce Tips Burning? A Grower’s Journey into the Science of Tip Burn

It always starts the same way: your lettuce looks healthy, vibrant, crisp. Then, just as the leaves begin to form that satisfying crown, you spot it—browning at the tips. The inner leaves, the most tender parts, turn scorched and unsellable. It’s disheartening. You think: kulang sa calcium. But is that really the problem?

This is the story of nearly every grower who has faced tip burn. And it’s more than just a nutrient issue—it’s a lesson in plant physiology, environment, and management.

The Misconception: It’s Just Calcium, Right?

Tip burn is commonly misunderstood as a simple calcium deficiency. However, experienced growers know that it’s not always about what’s in your nutrient tank. It’s about whether calcium is actually reaching the parts of the plant that need it the most.

Calcium is an immobile nutrient—it travels with water and only to parts of the plant that are actively transpiring. Young, inner leaves transpire less than older, outer ones. That’s why tip burn often begins right at the crown of the plant, where the tender, newly developing leaves are left underserved [1].

How Tip Burn Really Happens: A Closer Look at the Chain of Events

Let’s explore how multiple factors interact to cause tip burn. Each one plays a role in cutting off the calcium supply line.

First, consider the tropical climate in the Philippines. High temperatures combined with high humidity may seem like the perfect condition for plant growth. But paradoxically, this combo slows down plant transpiration. When the air is already saturated with moisture, the plant doesn’t release water vapor as actively. The older leaves, which can still transpire effectively, absorb most of the calcium. The younger leaves—especially those in the center—end up calcium-starved, leading to burnt tips [2].

Second, poor air circulation compounds the problem. When the growing environment lacks air movement, moisture clings to the surface of the leaves. This stagnant air layer acts like a barrier, slowing down transpiration even further. Without good airflow, nutrient movement within the plant is sluggish [3].

Third, low dissolved oxygen (DO) levels in the nutrient solution weaken the roots. Roots rely on oxygen to absorb water and nutrients effectively. When oxygen is deficient, roots lose their strength and efficiency. Even if your solution contains adequate calcium, weakened roots can’t deliver it where it’s needed [4].

Fourth, high Total Dissolved Solids (TDS) can throw off the plant’s internal nutrient balance. In a crowded solution, ions compete for absorption. Because calcium is immobile, it loses the competition to other, more mobile nutrients. The result: calcium is present but functionally unavailable [5].

Fifth, incorrect pH levels can cause nutrient lockout. Even if calcium is present in the solution, it becomes inaccessible when the pH is outside the ideal range. Lettuce thrives best when pH is between 5.5 and 6.5. Go outside that, and calcium becomes locked away from the plant’s roots [6].

Lastly, overly rapid growth due to high temperatures or excessive nitrogen can outpace the plant’s ability to deliver calcium to new cells. The newly formed leaves have weak cell walls and quickly dry out or burn—especially at the tips [7].

Managing Tip Burn: Practical Solutions from the Field

Prevention is possible—but it requires more than just adding nutrients. It demands a well-balanced environment and close monitoring of plant signals.

Start with Vapor Pressure Deficit (VPD), the difference in moisture content between the leaf interior and the surrounding air. This is what drives transpiration. A VPD between 0.8 to 1.2 kPa is considered optimal for lettuce. If VPD is too low, transpiration stalls; if it’s too high, water evaporates too quickly, leaving calcium behind. Managing VPD helps keep calcium flowing to where it’s needed most [8].

Next, improve air circulation. Use oscillating fans or natural ventilation to keep air moving throughout your grow area. Good airflow prevents moisture buildup, encourages steady transpiration, and ensures nutrients circulate efficiently through the plant’s vascular system [3].

Keep your reservoir well-oxygenated. Use air stones or oxygen diffusers to maintain high levels of dissolved oxygen. Healthy roots are the foundation of effective nutrient uptake. When roots are strong, they can keep up with the plant’s nutritional demands—even under stressful conditions [9].

Closely monitor your TDS and pH levels. Maintaining balanced nutrient concentrations and an ideal pH (5.5–6.5) prevents nutrient competition and lockout. Think of this as keeping the door open for calcium to enter and move through the plant [5][6].

In situations where environmental stress impairs root absorption, consider foliar feeding with CalMag. Spraying calcium and magnesium directly onto the leaves provides an immediate nutrient boost. Products like NutriHydro’s NH Bio CalMag are designed for this role. They combine calcium and magnesium with bio-stimulants to improve absorption and support cellular development during high-stress periods—without overselling or promising miracles [10].

A Grower’s Takeaway

Tip burn is more than a nutrient problem—it’s an environmental and physiological challenge. Understanding how calcium moves (or fails to move) through the plant can save your crops and your bottom line. From climate control to reservoir management and foliar support, preventing tip burn requires a grower’s full attention—not just a quick fix. 

References

1. https://www.pthorticulture.com/en/training-center/tipburn/

2. https://www.researchgate.net/publication/228493209_Tipburn_of_Lettuce

3. https://extension.psu.edu/preventing-tipburn-in-lettuce

4. https://www.sciencedirect.com/science/article/pii/S2214514117300123

5. https://www.simplot.com/agriculture/blog/understanding-tds-and-plant-health

6. https://www.nutrien.com/blog/why-ph-important

7. https://journals.ashs.org/hortsci/view/journals/hortsci/30/5/article-p1092.xml

8. https://www.arguscontrols.com/resources/white-papers/vpd-and-plant-growth/

9. https://maximumyield.com/definition/74/dissolved-oxygen-do

10. https://nutrihydro.com/products/nh-bio-calmag