How to

26 March 2021

How to Foliar Feed Marijuana Plants

When walking into the grow room first thing in the morning, you can always tell if a cannabis plant is happy. A flourishing cultivar will have branches spread wide, leaves tilted toward the light source, welcoming the new day. Other times, a particular plant in the room might look limp and weak as yellowing leaves begin emerging on lower branches.

Many variables could be causing the marijuana plant to look so sad. Under or over-watering could be a possibility, especially with down-turned leaves. Droopy leaves also reveal stress-induced from excessive temperature, humidity, or pH imbalances.

Discolouration of leaves is also indicative of improper watering techniques as lower leaves begin turning a light yellow. Often, nutrient deficiencies or build-up due to chemical overload are the culprits for leaf colour changes. growers must then determine what nutrient imbalances are affecting the plant.

A quick way to help the struggling cannabis plant overcome the sickly state is to apply a foliar spray directed towards the plant’s ailment to boost recovery. Spritzing the plant with some much-needed nutrient support may do the trick, depending on severity.

Even when they are not showing signs of distress, foliar feeding marijuana plants is a beneficial method of applying nutrients for quick up-take. As the fine mist showers over the plant, elements absorb rapidly through stomata pore openings on leaf undersides.

Cannabis plants generally flourish with foliar applications. Today we’ll take a closer look at how to foliar feed marijuana plants.

How Marijuana Plants Uptake Nutrients

Feeding cannabis plants the essential nutrients required for prime plant growth is mainly done through root drench applications. A well-rounded formula consisting of the big three – Nitrogen, Phosphorus, and Potassium (NPK), in addition to secondary and micronutrients, is sufficient for plant development.

Foliar spray nutrient doses, on the other hand, enter the leaves on a cannabis plant through tiny openings called stomata. These pore-shaped vessels open and close in response to light. As the morning dawns, stomata open wide and subsequently close during dark periods.

Stomata’s Role in Cannabis Plant Growth

Small guard cells are responsible for opening and closing stomata, expanding and contracting depending on different factors. Stomata are triggered to close by atmospheric conditions such as Vapor Pressure Deficit (VPD), excessive temperature, and humidity levels. Additionally, stress from pathogens, lack of water, and nutrient deficiencies signal stomata to close in response.

These tiny openings have several duties in their contribution to plant growth. First, stomata are responsible for the intake of the gaseous exchange of carbon dioxide during photosynthesis. During light hours, cannabis plants are highly active in synthesizing energy exchange. Stomata open the door for this essential function.

Stomata also play a vital role in regulating water movement through transpiration. The absorption of water is controlled through the tiny pores, closing if necessary to protect the plant from extreme conditions. If stomata remain closed for long periods, the marijuana plant cannot function properly, and the result is often not favourable.

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How Foliar Feedings Benefit Marijuana Plants

Foliar spray applications are particularly beneficial when specific nutrients, such as secondary elements Calcium, Sulfur, and Magnesium, are needed to boost a deficiency. They are an excellent method of supplying micronutrients such as Zinc, Iron, and Boron to aid in cannabis plant development. Foliar applications offer secondary support for NPK, coming to the aid during critical growth stages.

While foliar feeding is good practice in cannabis cultivation, and plants generally respond favourably to it, recognize it as a supplemental additive. Supporting the busy microbial environment within the rhizosphere with regular root feedings is essential to marijuana plant development. 

Mixing the Nutrient Recipe for Foliar Feeding

pH

As with everything else in cannabis cultivation, pH is a necessary component for healthy plant growth. If pH levels are not within ideal parameters, plants cannot absorb the vital nutrients required to grow.

Marijuana plants prefer a slightly acidic environment, performing well in pH ranges between 6.0 to 7.0 in soil and 5.5 to 6.5 in hydroponic and soilless substrates. When mixing foliar recipes, always check the solution’s pH to ensure it falls within these parameters.

Wetting Agents 

Surfactants are a beneficial addition to a foliar spray solution to help drive nutrients into cellular mobility. Without a wetting agent, foliar spray mixtures bead up and run off waxy leaf tissue. These active agents break the surface tension between the spray and the leaf surface, opening the door for nutrient-ready transport into the plant.

Start Low and Slow 

Always follow the manufacturer’s recommended dosing for foliar sprays. However, some product labels do not provide this information. A good rule of thumb is to lower concentrations of soluble nutrient formulas. This formulation helps the cannabis plant absorb elements easier and reduces the risk of nutrient burn.

When first starting, lower the parts per million (ppm) measurements of the nutrient recipe to see how the plant responds, gradually increasing ppm with favourable results. When unsure of a new nutrient recipe, it is always good practice to try it on a single plant before spraying the whole crop.

How to Apply Foliar Sprays on Cannabis Plants

The topside of cannabis leaves languishes in a cool-mist applied by foliar application. However, treatments to the underside are critical for nutrient uptake and pest eradication. Good spray coverage on the bottom side of the plant’s leaves encourages nutrient mobility through stomata’s open-door policy. Make sure the entire plant including undersides are fully covered when applying foliar nutrient applications.

On that same note, most invasive cannabis pest species seem to thrive on the bottom of the leaves, hiding their insatiable reproduction. Spray both top and bottom surfaces thoroughly when applying foliar sprays of either nutrient or pesticide inputs.

Cannabis grower foliar feeding a marijuana plant

When to Foliar Feed Marijuana Plants

The most effective time of day to apply foliar sprays is in the morning. When the sun begins to rise, or the grow lights come on in an indoor set-up, stomata open wide to get the day’s activities started. Just before the lights go off or as the sun sets is another good time of day for foliar applications.

Avoid spraying in direct sunlight during peak times of the day. Stomata will often close during intense heat halting activity. Instead of being absorbed, nutrient residue sits atop the leaf structure, frying in bright light and high temperatures. Nutrient burn is detrimental to cannabis plant growth, and this type of stress may take a long time to overcome.

Foliar Feeding at Different Growth Stages

Fresh cuttings, trying to establish a root system, often respond positively from low concentration spritzes of a light nutrient recipe. Start with a minimum dose on a few cuttings to see how they respond. Side-by-side trials at this stage are good experiments to learn more about nutrient dosing and plant response.

Young cannabis plants in the vegetative stage respond favourably after an early morning misting. Their leaves turn a dark, earthy green as they reach for the light. Weekly foliar sprays during this early growth stage support and encourages healthy plant development.

As the marijuana plant develops into the pre-flowering stage, however, transition off foliar applications. Sprays applied after flower development leave residual properties stuck in sticky trichome resin. Nutrient and pesticide particles can affect the taste, smell, and smoothness of the final product.

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Other Foliar Uses

Some cannabis insecticides and fungicides are administered through the root system to combat root dwelling infestations such as fungus gnats and root aphids. Other cannabis-loving pests prefer destroying leaf tissue, invading plant life above ground. Foliar sprays for these types of bugs directly target the infestation.

Spraying cannabis plant leaves with neem oil or insecticidal soap is a frontal attack on spider mites or aphid populations. While it seems impossible to defeat these nuisance pests, sometimes continued treatments are necessary to combat their destruction. Foliar applications are a beneficial means for pest control, directly hitting these pesky nuisances hiding under the leaves.

Foliar Spraying a Particular Cannabis Cultivar

Experienced cannabis growers and cultivators know that thick-leafed indica strains can be a challenge to achieve good foliar spray coverage over the mammoth leaf structures. Often inter-node growth is short and compact on these varieties, making it difficult to reach all leaf surface areas on the plant.

Fast-growing sativa cultivars, on the other side, grow tall and wide. Time spent treating these beauties to a nutrient treatment takes some time – but they will love you for it afterwards.

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Post author
Charle Thibodeau
Charle’ Thibodeau is a freelance writer with almost a decade´s experience, specializing in cannabis content for the past two years. A strong motivation to educate, inform, and promote the culture surrounding this miraculous plant is her earnest mission.
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