Why LED Interlighting Is Important for High-Density Vine Crops in Greenhouse

Cucumbers and tomatoes are two common high-value vine crops grown in greenhouses. Although they are different varieties, both are considered high-density crops. As these crops grow, especially during the later stages of vegetative growth and beyond, they tend to shade each other.

Many growers use trellises, scaffolding, or similar supports to encourage vertical growth. However, these measures alone are not sufficient to eliminate or significantly reduce the mutual shading effect, which can impact crop yield.

Why Not Just Increase Plant Spacing?

You might wonder: why not simply increase the spacing between high-density crops to reduce shading? That’s a reasonable thought. But whether through personal experimentation or insights from established planting practices, the reality is that every crop has an optimal spacing range that maximizes yield. Blindly increasing planting distance may actually reduce yields and increase horticultural investment risks.

The Rise of LED Grow Lights and Interlighting

So, what other methods can help boost production?

In fact, light intensity for high-density vine crops like tomatoes, cucumbers, and peppers decreases as canopy height increases. Younger leaves at the top absorb most of the light, leaving lower leaves shaded. As a result, productivity falls short of its full potential. In other words, if we can improve light penetration to the lower canopy, it’s highly likely that crop yields will increase and production potential can be fully realized.

To achieve this, interlighting grow lights are crucial for high-density vine crops. These lights provide sufficient illumination to the lower canopy, enabling more effective photosynthesis in shaded leaves.

The issue of insufficient lighting in the lower canopy was recognized by greenhouse growers long before LED grow lights were introduced, back when traditional HID and HPS lamps were widely used. Growers attempted to improve light penetration by reducing the distance between the lamps and plant tops, but the results were disappointing. These lamps emitted too much heat, damaging the crop leaves when placed too close.

The development of LED technology marked a turning point, making it feasible to place lighting closer to plant leaves without causing heat damage.

Combining Top Lighting and Interlighting for Optimal Results

Initially, during the rise of LED grow lights, the focus was on increasing lamp power rather than adjusting the distance between the lamp and the plants to improve light penetration to the lower canopy. Growers were often advised to use high-power top LED lights as supplemental lighting for greenhouse vine crops.

There were three main reasons for this recommendation:

1. To ensure crops could perform full photosynthesis.
2. To compensate for lower canopy shading by assuming a positive correlation between light power and penetration.
3. To achieve uniform illumination with a single light source, reducing costs.

While it’s true that higher power can improve optical penetration, the benefits are limited. The lower canopy of high-density vine crops still doesn’t receive adequate light.

In general, interlighting alone isn’t used as the sole supplemental light source for greenhouse crops. Instead, a combination of top lighting and interlighting offers the most effective solution for high-density vine crops.

If only the top canopy is illuminated, whether by sunlight or LED grow lights, our previous analysis confirms that the lower canopy remains underlit. Conversely, relying only on interlighting isn't ideal either. While the plants still receive sunlight through the greenhouse’s skylight, it’s not enough for complete photosynthesis. Evidence shows that plants benefit significantly when artificial light is added to supplement natural light.

By using interlighting, light intensity in the lower canopy increases, allowing older (but still productive) leaves to continue photosynthesis, which boosts fruit yield.

Is Interlighting Worth the Investment?

Ultimately, the decision is yours. Everything comes down to budget and whether the investment in additional interlighting will yield enough profit to justify the cost.

That said, several large greenhouse operations have already adopted interlighting to boost yields, like RIAT, an innovative agribusiness in Russia, Le Jardin de Rabellais and Tomwest in France, Wim Peters Kwekerijen in the Netherlands, and Fri-El Greenhouse in Italy.