Foliar feeding dates back to 1844, and has become one of the most popular plant-feeding methods. It allows growers to offer plants essential nutrients and minerals, which aid in strong and healthy plant growth.
Rather than solely using a soil-absorbed plant feed, foliar feeding focuses on a plant’s leaves: its foliage, hence the name. This is carried out using a sprayer and suitable diluted liquid feed. The plant foliage is misted with this nutrient-rich spray, which the plant then absorbs directly through its leaves.
This precise fertilization method was originally used within the agricultural side of horticulture. In fact, it has many advantages over traditional soil-based feeding regimes. Interest in foliar feeding has been growing within the houseplant and horticultural world for some time now, so I thought we’d take a look at exactly what benefits this relatively new fertilizing concept brings to your own plants.
Essential Plant Elements
Before we get into “what a foliar feed is” and “how to” articles, let’s first get to grips with why we need the addition of extra nutrients to keep our plants at their best.
We all know that plants need nutrients to grow strong and healthy, as well as air and water. In fact, some of you may be surprised to know that a total of 16 elements are needed for plants to grow strong and healthy. I’ve have made a list below of these essential plant element,s along with each symbol they represent in the periodic table of elements. These are the symbols you’ll see on pretty much every fertilizer packet.
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
- Nitrogen (N)
- Phosphorous (P)
- Potassium (K)
- Calcium (Ca)
- Magnesium (Mg)
- Sulphur (S)
- Iron (Fe)
- Zinc (Zn)
- Molybdenum (Mo)
- Boron (B)
- Copper (Cu)
- Manganese (Mn)
- Chlorine (Cl)
Of all these elements listed above, carbon, hydrogen and oxygen are all crutial for plant growth, but not considered plant nutrients, unlike the further 13.
Some nutrients are needed by plants in large amounts, and these are known as macronutrients. These include Nitrogen, Phosphorus, Potassium, Calcium, Magnesium and Sulphur.
You’ll recognise the three most important (primary) nutrients: Nitrogen (N), Phosphorous(P), and Potassium (K). All fertilizers that you buy will have an N, P, K value, usually listed as three numbers with dashes in-between. The N,P, K values are always listed in this format. Take a look at the picture below, and you’ll see this has an N, P, K value of 10-10-10. This is known as a balanced fertilizer.
Why do we need to Fertilize our Plants?
Well, as a plant goes through its many growth stages, it extracts and absorbs nutrients from the soil. Outdoor plants have many natural organic nutrients, such as humus, well-rotted compost and manures. They also draw from decomposed animal remains, leaf mold, micro-organisms etc.
Plants that are pot-grown have none of these natural organic nutrients. Slow-release fertilizers are often added to potting mediums and composts, giving a balanced plant feed for a couple of months. As time goes on however, your plant grows and extracts necessary nutrients from the potting soil. At some point, these nutrients have to be replaced, which is where plant foods or fertilizers come in.
The great thing about plant foods is that you can add specific nutrients, based on both the growing stage of your plant and the plant itself. For example, a fleshy green foliage plant will need less potassium (K), than a fruiting plant, but more nitrogen(N), which aids in healthy green growth.
All plants benefit from being fed when they’re in their growing season—not just pot-grown plants.
Farmers originally used fertilizers to guarantee high yield crops, especially on fruit and vegetables. Many farmers also alternate growing green manure crops which act as a natural soil improver, around their standard crops. Green manures have many benefits, they improve soil structure, replenish spent nutrients, attract beneficial insects and improve soil fertility.
Primary Nutrients and What they Do
The Importance of Nitrogen (N)
Nitrogen is the element needed in the greatest amounts. It’s a mixture of nucleic acids, proteins, hormones. and a major component of chlorophyll. The latter is the compound that plants use to transform sunlight energy into usable sugars from water and carbon dioxide. This is otherwise known as photosynthesis.
Healthy plants often contain up to 3–4 % nitrogen in their aboveground tissues. Furthermore, nitrogen is a fundamental nutrient required in all life forms. Plants with sufficient nitrogen quantities show rapid growth rates and large amounts of succulent green foliage.
The Importance of Phosphorous (P)
Did you know that 3/4 the phosphorous consumed within a plant’s life cycle will be in the first quarter of its life? You’ll find the largest phosphorous concentrations in the plant’s developing partst, such as roots, growth shoots and vascular tissues. It’s another necessary element used for cell division, and encourages buds, fruits, and flowers to form, develop, and ripen.
The Importance of Potassium (K)
Potassium is another indispensable nutrient for correct plant development. Adequate potassium prevents vulnerable, soft plant growth, making plants more winter-hardy, with greater disease and nematode resistance.
It also plays a role in the plant’s water and nutrient transportation. Potassium aids metabolism, helps plant fibre quality and development, and assists in essential protein and starch synthesis. Too little potassium in the soil can cause plants to have excessive water losses, resulting in dry, wilted plants.
How Foliar Feeding Works
Now that we’ve covered plant nutrient basics, lets talk about how foliar feeding works, exactly.
Essentially, this method is mostly used in fruit and vegetable production, where water-dissolved fertilizers are sprayed directly onto the leaves. The efficiency of nutrient uptake using this method is said to be 8-9 times higher than the traditional method, in which nutrients are applied directly to the soil.
Many people believe foliar feeding produces higher crop yields and better fruit quality. This method allows nutrients to penetrate the outer leaf cuticle. It then passes into the plant’s vascular system through direct leaf and stem absorption. At this stage, nutrient absorption by plant cells is similar to the absorption through the plant’s roots.
That said, it doesn’t take the place of good soil management, especially when it comes to using organic soil improvers. These include garden compost, leaf mold, and humus. All these are nutrient-rich, easily available, and priceless to any gardener—hobbyist and professional alike.
Foliar Feeding Benefits
Foliar feeding is particularly useful in specific growth stages. Remember that plants need different amounts of nutrients at different points in their life cycle. Foliar applications of essential nutrients at these stages can improve overall plant growth, yield, and crop quality.
Diverse environmental conditions cause many plant ailments by limiting root nutrient uptake. Additionally, flooding, drought, pest presence, wrong pH value, root disease, imbalanced soil nutrients can all affect root nutrient absorption. Foliar feeding is a powerful ally in these conditions.
Keep an eye of for nutrient deficiency signs so you can correct them quickly with a suitable foliar feed spray. Treating plants in this way respond rapidly, giving you time to deal with any necessary soil treatments. Soils can also have iron and zinc deficiencies, which foliar feeding corrects.
Of course, we all have to take into account the cost of fertilizers. Foliar feeding uses very small amounts of fertilizer, so it’s a low-cost alternative to traditional plant food,
Disadvantages of Foliar Feeding
Older plants, or those under stress conditions (such as drought and extreme heat or cold), have a thicker leaf cuticle. Remember that in foliar feeding, nutrients are absorbed through the leaves. As a result, these plants won’t be able to absorb nutrients properly.
Only a soluble nutrient mix can be absorbed by a plant’s leaves. Some fertilizers aren’t really soluble enough for use in a foliar feed situation, especially in cold water. Problems such as phototoxicity and leaf burn can be an issue.
Your feed’s pH levels can also have an affect on nutrient solubility, as well as the way the nutrients react with other water components. As a general rule, a feed with a slightly acidic pH value will improve nutrient penetration through the leaf’s surface.
Spraying your plants will increase humidity, which is fine when the plants are in a vegetative growth stage. It could, however, cause a problem at flowering time when humidity is already pretty high.
This can be a problem, and is caused by high nutrient and salt concentrations being left on the leaf cuticle once the water has evaporated. Always over-dilute your foliar feed solution a bit to avoid leaf burn issues.
Spraying your Plants
Once you have decided to give foliar feeding a go, there are a couple of factors to keep in mind.
When to Foliar Feed your Plants
We’ve touched upon a plant’s different growth stages and listed the overall importance of each primary nutrient. Foliar feeding is particularly beneficial through the vegetative growth stage and the bud/bloom production stage. Just don’t feed in this manner once your plants have bloomed, as it can cause bud mould and browning pistils. Not pleasant.
Throughout the growing season, it’s perfectly okay to foliar feed your plants once a week, ensuring you’ve diluted your fertilizer mix well. As mentioned, it’s best to over-dilute it to begin with.
What time of Day to Feed?
Choose either an early morning or late evening period when the leaf stomata are open. Try to leave as much time as possible for your plant to absorb the fertilizer spray, before daylight. When spraying indoor plants, always give them half an hour after lights out, enabling them to relax and their stomata to open. Don’t spray them under artificial lights, as the liquid will act as a lens and cause leaf burn.
I don’t recommend foliar feeding when temperatures are above 80 degrees F/27 degrees C. Your plants open and close their stomata to deal with extreme heat, release water, gases etc. and this could cause unnecessary problems.
Take good look round at suitable sprayers, before you invest. You really need one with a fine spray head, as you need to keep the fertilizing droplets small. Smaller droplets cover a larger foliage area and increase the efficiency of foliar feeding. It’s worth researching all-angle spray bottles, as their flexibility comes in quite handy.
Your spray volume should sufficiently cover your plants, but not leave them dripping. Cover all of the leaves and stems with a light spray. Too much feed will run off and be of no benefit at all.
It’s that easy!
Once you’ve sprayed your plants, just sit back, relax and notice the difference.
I’m sure you too will be converted to adding foliar feeds to your plant’s fertilizing regime. I’ve worked in tropical nurseries and we always used to use a seaweed foliar feed, once a week. Seaweed is one of the most popular organic feeds, high in trace elements and natural growth stimulants. The results were simply amazing, especially with the Spathiphyllums, Philodendrons and Marantas.
I wouldn’t completely swap to foliar feeding. That said, used alongside soil conditioners and traditional soil-fed fertilizers, it can make a big difference to our plants. After all, happy plants, happy you!