How To Fertilize Orchids: Beyond The Basics

When you first start learning about how to fertilize orchids, using an all-purpose orchid fertilizer such as a 20-20-20 NPK mix with micronutrients will be suitable for many varietals. However, as the variety of orchids in your collection grows it will likely become necessary to learn some more advanced knowledge and techniques about how to fertilize your orchids. Different species of orchids may require different levels of nutrients. This will be apparent when you see that some of your orchids are thriving while some seem to struggle. Perhaps you have a very healthy plant, but it never puts out a flower spike, or the leaves on another type of orchid are going yellow.  While there may be other reasons, such as light or temperature, over or under watering that may be contributing to this problem, it is more likely be a macro or micro nutrient deficiency and we may need to adjust the fertilizing formula to remedy the deficiency. 

Water Basics

Let’s start with the first and most important part of our fertilizer mix and an often overlooked detail in how we fertilize orchids, and that is the water that we use to water/fertilize our plants with.  While our natural inclination is to use tap water to mix with our fertilizer, this can actually be detrimental to our plants. We don’t know whether we are using hard water or soft water and we don’t know the PH. These are important things to know before you start adding fertilizer nutrients. You have now reached a point in your orchid growing career where it is time to invest in a simple TDS (total dissolved solids) meter and a PH meter. These two simple tools will be used so that you can make adjustments to the levels of nutrients that you are giving your plants. If you have a lot of orchids, it would also be very helpful to invest in a reverse osmosis watering system. It is not only good for your plants, but it is good for you also. I never drink unfiltered tap water, and the taste of water from a reverse osmosis system is so much better than chlorinated and fluoridated water, and it also removes many other impurities from your water. If you do not have a reverse osmosis water system, the next two best choices are to use either distilled water, or to collect rain water for the purpose of watering your orchids.  

Total Dissolved Solids (TDS)

What are total dissolved solids and why is this an important factor to know when it comes to knowing about how to fertilize orchids? Total dissolve solids (TDS) are a measurement of the combined amount of metals, minerals, salts and other materials present in the make up of water. It may contain pesticides or added chemicals from run off or from municipal water treatment, such as the addition of chlorine and fluoride which are used by many water municipalities. It tells us how pure, impure, hard or soft our water is. Personally, I never drink municipally treated water, and the first thing that I install wherever I am living is a reverse osmosis water system. By using rainwater, distilled water, or reverse osmosis for watering our plants, we are starting at near a level of purity as a control basis point for fertilizer measurements. If you wish to learn more about total dissolved solids, there are many sources of more detailed information, you can visit the Safewater site here


Now that we have a basic understanding about TDS and why we should always use rainwater, distilled water, or reverse osmosis water, how do we apply this knowledge? In nature, an orchid would receive its nutrients in rainwater. Some studies have been done that show rainwater typically has between 20 and 50 ppm (parts per million) of total dissolved solids. This tells us that orchids would typically receive all their nutrients in low levels. We can be a little more generous with feeding our orchids in terms of the total ppm. A safe range to aim for is between 120 to 160 ppm of total combined nutrient content of macro and micro nutrients. We can use this guideline if we are simply using an all purpose orchid fertilizer or whether we are custom designing a fertilzer mix combination. For example, let's say that we were combining a Calcium Nitrate, Epsom Salts, Kelp, and a macro/micro nutrient combination, the total dissolved solids should never be more than 160 parts per million. With the aid of a TDS meter we can keep track of the amount of nutrients that we are adding. We only need to add a pinch or few drops of the various nutrients, a little goes a long way. Remember the old adage, water weakly, weekly. We go into more detail on mathematical calculations and ratios when combining nutrients in our upcoming eBook on orchid care. Knowing how to use a TDS meter will become very helpful when we need to vary the nutrients and the ratios for individual plants and species as we learn to diagnose nutrient deficiencies. 

PH And Its Importance

PH is a measurement of water alkalinity or acidity. It is measured on a scale ranging between 0 and 14.  A measurement 7 being neutral, below 7 is acidic and a measurement of above 7 is alkaline.  Rainwater can have a range of between 5 and 7 on average and typically has a mean average of 5.7. PH plays a vital role in nutrient uptake and is an important component in how we fertilize orchids. Most nutrient uptake occurs in the sweet spot PH measurement of 5.8. This measurement is a good target to aim for when mixing or fertilizer with water. After we have added the desired amount of fertilizer to our watering mix we can adjust the PH by using a hydroponic PH up or PH down solution. We only need a little of either of these solutions, a few drops will go a long way. Add a few drops, stir the water/fertilizer mix and test, add a few more drops if necessary. One note to keep in mind, is that while a PH of 5.8 is the ideal target for most nutrient uptake, it is ok and beneficial to vary the PH level between 5.5 and 6.5 on occasion to allow for better uptake of some macro or micro nutrients that might otherwise not absorb as well at PH 5.8. Other factors in determining what PH level we need to use include the type of medium that we are using and the species of orchid that we are growing. We may need to make adjustments in PH according to these factors. 

Putting It All Together

Our goal at Heavenly Orchids is to provide you with knowledge on how to make orchid care easy. In learning how to fertilize orchids there is no one size fits all guideline, because of the many factors involved, whether it be the species of orchid, the varietal, or the potting mix. However by following the guidelines on this page, you will be able to use more precise measurements to take care of a broad variety of orchids by using one of the recommended water sources, keeping the totals dissolved solids (TDS) to around 160 ppm per feeding and aiming for a 5.8 PH with most feedings. As you gain experience and learn to diagnose nutrient deficiencies, you can adjust the fertilizer ratio and vary PH level to target optimum nutrient uptake in the nutrient deficient element.