The Common Mistake To Avoid When Using Liquid Fertilizer On Your Leafy Greens

In theory, gardening is quite simple. With healthy soil and an eye for watering needs, you'll likely enjoy the fruits, vegetables, or blooms of your labor. However, for a garden to fully thrive, you need to go above and beyond, like adding soil amendments and of course, applying fertilizer. Liquid fertilizer is often used to boost plant health and quickly replenish nutrients, and many gardeners spray the fertilizer straight onto the leaves. But this method can damage leafy greens, so it's best to avoid it.

While there are seemingly endless techniques for fertilizing your plants (as seen in the many TikTok fertilizer hacks), only two types of products are commonly found in gardening stores: liquid fertilizer and dry or granular fertilizer. Granular fertilizer is most common. But liquid fertilizer is gaining popularity because it's easier to apply, delivers nutrients more quickly, and provides more consistent nutrients in every drop. For heavy feeders like leafy greens, those benefits can be particularly helpful.

But how you deliver liquid fertilizer matters, especially for the tender leaves of leafy greens like lettuce. It's tempting to spray fertilizer on leaves; if you see the mist on the leaves, there's peace of mind that the fertilizer is on the plant, versus pouring liquid into the ground and hoping that it reaches the roots. However, a bit of faith is needed here, since foliar application — if done inappropriately — can lead to burnt leaves, a reaction from showering your plants with nutrients. 

If foliar application has been your go-to technique, don't panic. Your leafy greens are likely still benefiting, but possibly not to the extent that you'd like. First, let's talk about plant biology. Just like the pores we have on our skin, leaves have microscopic openings called stomata and minuscule micropores in the waxy layer of the leaf surface. Combined, these openings absorb only about 15% to 20% of any substances applied foliarly, due to the placement of the stomata on the undersides of the leaves and the waterproof nature of the micropores. 

For this reason, liquid fertilizer can be less efficient when applied to the leaves and, from a financial standpoint, is largely wasted. More importantly, leafy greens are at risk of leaf burn if they're foliar fed, especially in intense sunlight, on a hot day, or if the fertilizer is sprayed too heavily. Applying fertilizer during the warmest times of the day also can cause the liquid to evaporate before the leaves have any chance to benefit.

Foliar application, however, can be effective for delivering nutrients quickly to plants that are showing signs of deficiency and need immediate TLC. Otherwise, for most leafy greens, applying liquid fertilizer to the soil (such as this DIY fertilizer for leafy greens) around the base will more effectively deliver what the plants need and reduce the risk of leaf burn.