A Play-by-Play on Plant Nutrition

Regardless of whether the ingredients in your fertilizers are from organic or synthetic sources, all fertilizer programs have at least one thing in common: nutrients. The term nutrient has started to blend fluidly into the vernacular of the hobby grower, meaning it has come to stand for more or less anything added around the base of plants to improve growing conditions.

For the sake of this article, the term nutrient is used to describe any chemical element essential to plant growth. Additional products that don’t meet the parameters of the aforementioned are generally considered supplements. Supplements are categorized similarly to nutrients, but for some products there are sometimes grey areas as to where certain products fit in.

When building a high-yield fertilizer program, it is common to use both nutrients and supplements. The parameters of the garden, such as nutrition levels, root health, TDS, pH and EC, must all be closely monitored when deciding what will go into your nutrient solution, as these often change throughout the duration of the plant’s life cycle.

Email Newsletter

Join thousands of other growers who are already receiving our monthly newsletter.

Nutrients for Seedlings

Unless you are starting with a clone, plants begin their life cycle in the seedling stage, when roots and leaves begin to sprout from the seed as a result of germination. During this initial phase, you should start your plants off on a light fertilizer program. You should aim to keep your pH relatively constant throughout the life cycle, usually somewhere between 5.4 and 6.5 in hydroponics, as the nutrient regimen you use typically has a target pH range that provides plants with the greatest potential of nutrient uptake ability.

As soon as you start adding ingredients to your media, it is important to monitor your solution regularly. EC, or electrical conductivity, measures the potential of a given solution to conduct electricity, typically displayed in μS/cm (microSiemens/cm). EC is considered the most universal method of ion measurement, but some growers prefer to monitor their solutions in TDS (total dissolved solids), which is displayed in ppm (parts per million). The difficulty with measuring TDS is that different scales are used around the world, so these readings aren’t universal.

Generally speaking, the relationship between EC and TDS is fairly linear in dilute and moderately concentrated solutions, but tends to drift in more heavily concentrated solutions. Total dissolved solids can be anything in the solution producing a charge, including the nutrients and supplements you do (or don’t) add, impurities in the water, or any other organic and inorganic substances present. These numbers serve as reference points to help you make decisions based on the needs of your specific crop. For ease of explanation, I will focus on how EC affects fertilizer programs, specifically in hydroponic systems that use soilless media.

You don’t want to shock young plants with an overload of product, so you should keep the EC low, between 0.5 and 1.0 μS/cm. A large percentage of that reading should be composed of nitrogen, since the main goal during this stage is to encourage vertical growth and generate foliage. In organic fertilizer programs, nitrogen may be present in various natural forms, which must undergo one or more processes to convert it into a usable form through the work of micro-organisms. However, the nitrogen present in synthetic or inorganic fertilizers is usually in a form that is readily available to plants right out of the bottle, such as nitrate (NO3) or ammonium (NH4).

Nutrients for Mid-to-late Veg

As plants continue to grow, their demand for a diverse blend of critical nutrients begins to increase. This blend should be comprised of some balance of the three primary macronutrients (nitrogen, phosphorus and potassium), and the three secondary macronutrients (calcium, magnesium and sulfur). Plants will also require six micronutrients: iron, copper, boron, molybdenum, manganese and zinc.

Keep in mind that macronutrients are not necessarily any more important than micronutrients; the term macro is simply an indicator of the quantities of these nutrients required for prolific growth. Macronutrients tend to be present in plant tissues as tenths of a percent and higher, while micronutrients are more commonly quantified in terms of parts per million. Think about this in terms of a multivitamin.

Some of the vitamins in multivitamin formulas for humans are present in smaller quantities than others, but they all play a part in working together to be beneficial. Plant fertilizers are designed in much the same way.

Nutrients for Early Bloom

As plants progress, their needs are steadily shifting. The likelihood of a nutrient imbalance is highest during transitional phases, as there are multiple factors influencing the changing environment. One shortcut to identifying a potential deficiency is to pay close attention to how your plants react to their environments. Once things like lighting, humidity and temperature are ruled out as the cause of any strange symptoms, you can begin to consider a possible nutrient imbalance.

Certain nutrients such as nitrogen, phosphorus, magnesium and potassium are all considered mobile nutrients, meaning they move freely within the plant to areas where nutrients are needed most. In the case of early blooming, this is the new growth and youngest leaves. If older growth appears to be stressed, the plant might not be getting enough nutrition to supply all its parts. Look for deficiency symptoms in the older leaves to determine if there is a shortage of mobile nutrients being supplied, and then look a little further to identify which mobile nutrient appears to be lacking.

If you are seeing symptoms of stress on the new growth, it might be that plants are deficient in immobile nutrients, such as sulfur, calcium, iron and copper. During the early blooming stage, it is important plants get adequate amounts of all of these to promote continuous strength-building and structural growth, as well as prepare the soon-to-be transitioning plants for the flowering stage.

Similar to the transplant period in early veg, tread lightly when altering your feed schedule for changing conditions, as plants tend to adjust best when changes are made gradually. The target EC level for late veg through early bloom should be between 1.3 and 1.6. The composition of these numbers should begin to shift steadily away from high levels of nitrogen to higher levels of phosphorus and potassium.

Full Bloom and Maturation

If you’ve made it to the flower and fruit production stage, your main concern at this point is likely going to be maximizing your yields. Root health is particularly important here. The roots of plants are largely responsible for respiration and the uptake of nutrients and water for the entire plant. Encouraging robust root growth is especially encouraged because as the surface area of healthy roots increases, plant processes will be more optimized leading to high-yield plant production.

Organic hydroponic growers often use micro-organisms such as mycorrhizae to help promote robust root development, while non-organic growers may turn to products such as hypochlorous acid, which has visually similar effects on plant roots as do beneficial micro-organisms. Using one of these methods is recommended to increase root health when used in conjunction with a high-yield fertilizer.

Once your plants reach full bloom, it is recommended to keep your EC between 1.8 and 2. Their demand for phosphorus and potassium is at an all-time high right now. Look out for deficiencies in the mobile macronutrients and adjust your recipe accordingly to help plants through the rigorous reproductive phase they are going through. After 6-8 weeks of flowering, you will notice your plants have stopped reproducing. Now is the time to wean your plants off their high-yield fertilizer program in preparation for harvest. During the final 2-3 weeks of flowering, the target EC should also be decreased to between 1.5 and 1.7.

Flushing the System

More experienced growers like to flush their entire system with plain water, or plain water plus a flushing agent, during the final 7-10 days before harvest to help remove any residual mineral buildup in the system and the plants. An accumulation of these salts has been known to cause a bitter taste in the subsequent harvest.

Descaling agents such as hypochlorous acid can also be used to help aid in the flushing phase, as it breaks down calcium and magnesium salts that have built up over the course of the grow cycle. To ensure as much residual salts as possible are removed, it may be necessary to flush more than once before harvest.

Responding to the reactions of your plants is one of the best ways to achieve maximum yields. You can follow these guidelines or other feed schedules exactly, but depending on the crop and a variety of other circumstances, the demands of your plants will vary.

There is no universal recipe out there that will satisfy the tastes of all plants, making it difficult to design a one-size-fits-all fertilizer program. Using these tips, along with the latest technologies available to creatively and resourcefully guide your plants through their journey, will be your key to creating the ultimate fertilizer program.