1. Indoor-Plants-led-grow-lightOne of the common questions that customers ask is how to fertilize plants grown in Sunshine Advanced (SSA) mixes. Many are confused by all of the information about fertilization available on websites, in magazines, or product guidelines that may contain conflicting advice and opinions. The approach to fertilization should not be that difficult. We want customers to succeed when using our high-quality products, and part of that success relies on knowing the basics when it comes to ‘nutes’ (nutrients) and indoor growing with SSA mixes.

    Let’s start with some clarifying facts about Sunshine Advanced products—beginning with a summary from SSA Tech Sheets and Product Labels:


    Sunshine Advanced Mix #4 - OMRI-listedSunshine Advanced Mix #4:

    Ingredients: Canadian Sphagnum Peat Moss, Perlite, Coir, Dolomite Lime, Gypsum, Organic Fertilizer, Proprietary Blend of Endomycorrhizae, and Organic Wetting Agent. Plus RESiLIENCE®!

    Fertilization: Start your own feeding program within 7 days of planting or seedling emergence.


    Sunshine Advanced Rain Forest Blend - OMRI-listedSunshine Advanced Rainforest Blend:

    Ingredients: Bark, Coir, Perlite, Compost, Earthworm Castings, Organic Fertilizer, Proprietary Blend of Endomycorrhizae, and Organic Wetting Agent. Plus RESiLIENCE®!

    Fertilization: Start your own feeding program within 14 days of planting or seedling emergence. (14 days rather than 7; the earthworm castings give a little extra nutrient boost.)


    7106sunshine-mix4-myco-resilience-frontSunshine Advanced Mix #4 with Myco

    Ingredients: Canadian Sphagnum Peat Moss, Perlite, Dolomite Lime, Low Phosphorus Fertilizer, Proprietary Blend of Endomycorrhizae, and Wetting Agent. Plus RESiLIENCE®!

    Fertilization: Start your own feeding program within 14 days of planting or seedling emergence. (14 days rather than 7; the earthworm castings give a little extra nutrient boost.)

    Sunshine Advanced Ultra Coir - OMRI-listedSunshine Advanced Ultra Coir:

    Ingredients: Coir, Canadian Sphagnum Peat Moss, Perlite, Proprietary Blend of Endomycorrhizae, and Organic Wetting Agent. Plus RESiLIENCE®!

    Fertilization: Start your own feeding program within 7 days of planting or seedling emergence.


    Sunshine Advanced Mixes are formulated to have an acceptable pH and low level of all the necessary nutrients for plants or seedlings to get a great start. But these starter nutes are not for the long haul. After 7 to 14 days and at least 2 to 3 waterings (seedlings usually require more), the grower will need to begin a feeding program.

    When it comes to fertilization, it’s safe to assume that fertilizers will be dissolved in a grower’s irrigation water. These fertilizers can be bought in a liquid or powder form. Powder forms are often called “water soluble fertilizers.” So, let’s dig in by covering the five most common things that can go wrong with fertilization regimes, followed by ways to overcome these common problems.

    The five most common fertilization problems:

    1. Not considering the water quality (Poor water quality can derail even the best fertilizer choices.)
    2. Getting too wrapped up with ppm, EC and translation into percentage N (Electrical conductivity (EC) or parts per million (ppm) is usually a measure of the “strength” or the concentration of fertilizer put on your plants.)
    3. Thinking that all fertilizers have the same basic ingredients (Different fertilizers may have different ingredients, which is important.)
    4. Fertilizing with the wrong formulations
    5. Over-fertilizing or fertilizing too often

    Water Quality

    This is probably the most important issue in growing. Greenhouse growers are very aware of the impact of water quality on the success of growing crops. Water that has a high amount of dissolved lime (i.e. high alkalinity or bicarbonates) or a high amount of salt (i.e. high EC) will create a challenge for growing plants. Having water tested by a reputable lab, will tell a grower what he or she is dealing with.

    Once water issues are resolved, one can effectively choose what type of fertilizer to use. But it’s also smart to think about what type of mix is best for a given water situation. For example, at Sun Gro we usually recommend a more porous mix when dealing with poor water quality – like our Sunshine #4 Mix or our Sunshine Super Hydro where the built up salts at plant root zones can be “leached out.” This will be covered in more detail later in the article.

    EC or PPM 

    Forget about “ppm’s” and EC for right now.  There are so many methods used to figure out these two numbers, some right and some, well, not so right. This is where some growers make things more complicated than they need to be. They throw the baby plant out with the water by getting too analytical.

    The problem is that electrical conductivity (EC) or parts per million (ppm) is used to measure the amount of salts or specific nutrients in water, fertilizer solutions and soil (using some type of soil extraction method). They are not often interchangeable, but some growers treat them like they are, which leads to lots of misconceptions.

    Sunshine Advanced mixes have been formulated to achieve an acceptable starting pH and nutrient content, so growers should be okay with simply choosing a fertilizer. There are many fertilizers to choose from. We usually recommend using either a water soluble or liquid concentrate fertilizer for indoor growing – either will work. We don’t recommend slow-release prills because these are better for outdoor growing.

    Fertilizer Ingredients

    One very important thing that a lot of people don’t think about is the ingredients or actual compounds that make up a fertilizers. The first thing to know is that all fertilizer labels tell the makeup and ingredients in the product. This is called the Guaranteed Analysis. The major nutrients reported are nitrogen (N), Phosphoric acid (P2O5) and Potash (K2O), typically referred to as Nitrogen, Phosphorus and Potassium (N-P-K), and they correspond with the three numbers on a fertilizer label (e.g. 4-1-5). It’s always important to read the analysis.

    Nitrogen, the ‘N’ number, can be provided in various forms. The major nitrogen forms in most water soluble or liquid fertilizers are Nitrate (NO3-N), Ammonium or Ammoniacal (NH4-N) or Urea (NH2)2CO. Urea usually converts to Ammonium N in the soil, so most experts consider this an Ammoniacal source of Nitrogen. Plants respond differently to these different sources of N. Nitrate is much slower to assimilate, whereas Ammonium is the more readily assimilated in the plant. Too much Ammoniacal N is not necessarily a good thing, and for indoor growing it is best to have a “balanced’ ratio of nitrate to Ammoniacal Nitrogen or one that is higher in nitrate.

    What a lot of people don’t know is that using fertilizers high in Nitrate (NO3 – N) tends to increase growing medium pH, and high Ammoniacal (NH4 – N) fertilizers tend to decrease media pH. As mentioned, many fertilizers will have both types of Nitrogen in the right proportions so as not to affect the pH of the media. Bear in mind that this process is a slow one, taking weeks or even months.

    The lime charge blended into Sunshine Advanced mixes keeps the pH from dropping too low. Residual lime in media (if lime has been added to the mix at some point after planting) can also counteract the acidic effect of Ammoniacal Nitrogen.

    Choosing the Right Formulations

    Nitrogen is important to crops during their vegetative growth stage. When moving into the flowering and then fruiting stage, the amount of nitrogen can and should be lowered to avoid forcing vegetative growth. Phosphorus (P2O5) is necessary for the development of roots, and as plants mature Phosphorus moves into the flower bud and then into the fruit (seed). The key here is to provide an adequate amount of P. (Adding more P does not necessarily mean bigger or more flowers and fruit!)

    Most fertilizer formulations do not have a higher percentage of phosphorus as compared to Nitrogen or Potassium. In fact, we recommend a low percentage of Phosphorus. This is because the mycorrhizae in the Sunshine Advanced mixes do their best work (extending out into the mix to grab nutrients and water for the roots) when the Phosphorus level is low, providing an adequate amount of P to the plant. We recommend a middle number lower than 10, such as 4-1-5 for vegetative growth, or 1-4-5 for flowering.

    Potassium, usually expressed as K2O (soluble potash), is good for all stages of growth. It is usually added to increase a plant’s resistance to stresses and is essential to the development of chlorophyll. It also is integral in transpiration by regulating the opening and closing of plant stomata, which allows plants to make better use of light and oxygen.

    Secondary Nutrients (such as Calcium, Magnesium and Sulfur) and Micronutrients (such as Iron, Manganese, Zinc, Copper, Boron and Molybdenum) are also included in a good fertilizer, which means that no additional products are needed. You don’t have to break the bank once you find a well-formulated fertilizer. Generally speaking, very clean waters, or using reverse osmosis (RO) water, will usually require a fertilizer containing Calcium and Magnesium. The use of Dolomitic limestone as the liming source in Sunshine Advanced products helps provide needed Calcium and Magnesium.


    It’s always better to under-fertilize rather than over-fertilize. Never make the dilution stronger than recommended on the package. If deficiencies are noted along your growing timeline, have a media analysis done as well as a tissue analysis to get a clear picture of what is going on. Then the correct additional nutrients can be applied. Guessing almost always leads to mistakes!

    Bear in mind that plants get to a point where they can’t take up any more nutrients, and so the fertilizer is wasted. This can also cause problems, such as clubbing and the encouragement of unwanted microorganisms.

    Hopefully, this information will help indoor growers make better decisions when it comes to nutes and growing with Sunshine Advanced mixes. Those looking for even more good information should pick up the reference book Water, Media and Nutrition for Greenhouse Crops, edited by David William Reed. It’s a great resource.

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