How And When To Use Foliar Spraying

Not all growers may be familiar with it, but most will at some point encounter a scenario where they should apply a foliar spray to their cannabis plants. The reasons for this are various; from treating your plants with insecticides or fungicides, to addressing a nutrient deficiency in the fastest way possible.

While foliar spraying (or foliar feeding) your plants doesn’t really require any special growing skills, it can nevertheless be helpful to know how to do it right so you can get the best results. Let us take a closer look at foliar spraying; what it is and when you want to use it.

What Are the Benefits of Foliar Spraying and When to Use It?

Foliar feeding does not replace the normal process by which plants uptake nutrients. This happens through your plants’ roots that are embedded in soil or some other growing substrate. Foliar feeding, however, can be a very effective way of supplementing nutrients in the short-term. It is particularly effective if you want to provide your plants with secondary nutrients like magnesium or calcium. It is also a very beneficial way to provide zinc, iron, manganese and other micronutrients to your plants.

What makes foliar feeding so special and an excellent way to address any type of nutrient deficiency is that spraying is much faster compared to applying nutrients to the soil via irrigation. The majority of the nutrients that you spray directly on your plants' leaves will be absorbed in a very short time. The plants will also take in a much higher percentage of the nutrients this way. Studies have shown that foliar feeding is as much as 95% effective. This means plants take in almost all nutrients administered by spray, while they uptake a smaller percentage when fed through the soil.

In addition to speed, foliar feeding has also other positive effects. When the plant is taking in nutrients via its foliage, this causes it to give off more carbohydrates into their root zone. This is beneficial for the microorganisms in the growing substrate that help assist with nutrient uptake.

One other benefit of foliar feeding nutrients is that it entirely forgoes the potential problem of nutrient build-up in the soil. Accumulated minerals, salts, and nutrients is a very common problem with cannabis growing. When this happens, the pH of the soil is usually off, which leads to nutrient lockout.

Foliar Spraying for Fungicides and Insecticides

Foliar sprays are a common and effective way to treat your plants for many cannabis pests and diseases such as mites, powdery mildew and others. One popular substance that acts as both an immediate treatment and preventative measure is neem oil.

Neem oil has the advantage of being a natural insecticide that also has some fungicidal properties. Cannabis growers use a neem oil foliar spray together with aloe vera juice and some type of emulsifier like potassium silicate to dissolve the oil. Weekly sprays during the vegetative phase can strengthen plants and increase their resistance against pests and pathogens.

A foliar spray made with potassium soap (insecticidal soap) is an excellent option to take on and then take out various harmful insects. It is particularly effective against aphids, which are some of the most common cannabis pests. A mix of neem oil dissolved in potassium soap is doubly effective. The potassium soap gets rid of the pest on contact, and the neem oil helps prevent future attacks while strengthening your plant’s defences.

Many other natural ingredients, from cayenne pepper to nettle, cinnamon oil, and even plain milk can help combat powdery mildew and other fungal pathogens naturally, without causing any harm to your plants. If you look around on grower forums and websites, you can find many recipes for such natural foliar spray mixes.

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Foliar Spraying for Grow Boosters and Stimulants

Because of the fast-acting way that nutrients can be provided to your plants via foliar application, this also makes it effective for providing your crops with boosters and stimulants when they need them. There are a wide range of products out there, most of which require foliar feeding as the method of application.

Some growers make their own foliar growth stimulators, for example by mixing liquefied aloe vera leaves with water or by using any number of DIY foliar stimulant recipes that you can find online.

How to Foliar Spray Your Cannabis Plants

1. The best time for foliar spraying is either early in the morning or late in the evening. If you grow outdoors, buds getting wet can be a normal occurrence due to rainy weather. If a spray with some type of fungicide is the only way to save your precious outdoor crops from a mould infestation, use a natural, safe, and residue-free product only.
2. Do not spray in direct sunlight. The sunlight can not only burn your plants through the “lens effect” from droplets on the leaves, it can also degrade active substances and nutrients contained in your solution. In the evening, the plant’s pores are fully open, which allows for a quicker intake as compared to during the day. If you grow indoors, the best time to spray is at the beginning or the end of the dark period.
3. Avoid spraying when it is too hot or too cold. In hot temperatures, your plant’s stomata (the pores in the leaves) will be almost closed, making a foliar spray much less effective. On the other hand, when it is too cold, spraying could promote fungal growth. Spraying early in the morning can be best since this allows your plants to dry during the day, reducing the risk of mould.
4. Don’t spray when you expect bad weather. Rain can make your foliar spray a waste of time by washing away or diluting your spray solution. The same goes for strong winds. When you spray outdoors, wait for rain and stormy weather to pass. When you spray indoors, it can be a good idea to turn off ventilation fans for an hour or two. This allows the solution to be absorbed by the plants without any major disturbances.
5. Don't forget the undersides. When you spray, spray the entire plant - in particular the undersides of the leaves. There are at least two good reasons for this. Many pests, such as spider mites and other aphids are often located on the leaf undersides. This is also where more of the stomata are located.
6. Take note of the recommended nutrient strengths of your solution. Most of the time, foliar feeding requires a much lower nutrient strength than feeding your plants through soil. If the product that you are spraying doesn’t specify the proper amount for foliar application, start with half the recommended dose.
7. Test your spray first to ensure that your plants won’t get irrevocably damaged. Rather than going full-out and spraying your entire crop with an untested product you just got from the internet, perform a test on one single leaf first. Wait for a day to see whether the application caused any damage before moving forward with a full feeding regimen.
8. Avoid spraying during flowering. Spraying the buds can be bad for a number of reasons. Depending on your spray solution, this can lead to anything from a spoilt taste to an increased chance for mouldy buds.

⚠️ Safety is Key

Always follow the safety instructions. Some commercial sprays may be safer to use than others, but you should always follow the guidelines for safe use. You obviously don’t want to spray potentially harmful substances without adequate protection such as gloves, a face mask, and protective eye gear. Make particular note of how safe the product is to spray on something that you will consume after harvest. Some commercial insecticides or fungicides may work great for ornamental plants, but they can be harmful if not outright toxic for vegetables and of course, for your precious weed! So always read and follow the instructions carefully before you spray.

What is the Best Type of Sprayer to Use?

There are two main types of sprayers available that you can use for foliar sprays; both types are useful depending on the circumstances.

One type is a simple hand-sprayer that may take 500ml to 1l of spray solution. These small and handy sprayers are great if you only have a few plants or if you require a sprayer for some “precision work;” for instance, when you want to avoid spraying buds.

The other types of sprayers are garden pump sprayers. These come with different capacities and a shoulder strap so you can carry them around easily while attending to your plants.

These pump sprayers also come with an extended spray wand which makes them especially convenient so you can spray your plants easily from all sides, including the underside of the leaves where it counts.

The best is when you get both types of sprayers so you have them handy when you need them. There will always be times where the bigger pump sprayer will be better to use and then there are situations where you want the small hand-sprayer instead.

By foliar spraying your cannabis plants, you can effectively combat all sorts of problems like pests and mould. It also an excellent way to provide plants with nutrients or stimulants in emergency situations. With the tips in this article, foliar spraying your cannabis plants shouldn’t be a mystery any longer!