So what is fertilizer? To keep it simple, fertilizer is NOT food. The plants themselves make their own “food” –sugars, basically – through the photosynthetic process– sun (trapped by chlorophyll) + water + carbon dioxide going into the leaves = oxygen going out and sugars going down to the roots and to the rest of the plant.
FOR those of you that have seen the original or remade version of the movie “Little Shop of Horrors”, you will remember Seymour Krelborn’s quest to find just the right fertilizer to keep his other-worldly plant Audrey II alive. Unfortunately, it required dining on unsuspecting but seemingly deserving victims. Fortunately, most species of plants used for bonsai are not man-eating, but that doesn’t make our task of finding the right fertilizer any easier!
So what is fertilizer? To keep it simple, fertilizer is NOT food. The plants themselves make their own “food” –sugars, basically – through the photosynthetic process– sun (trapped by chlorophyll) + water + carbon dioxide going into the leaves = oxygen going out and sugars going down to the roots and to the rest of the plant. Fertilizer is actually a collection of macro and micro-nutrients that are required for plants to grow healthy. The nutrients act as catalysts to aid and support the plant as it develops its own food. Macro-nutrients include nitrogen, phosphorus, potassium, calcium, sulfur and magnesium. Micro-nutrients include, iron, copper, zinc, chlorine, Boron, cobalt, manganese, molybdenum and nickel. Some fertilizers may also include other trace elements and beneficial bacteria and fungi. In other words, using fertilizer is basically like us taking our vitamins and minerals.
Before we discuss fertilizing regimens, it’s important that we talk about the environment we will be fertilizing in. The bonsai’s environment is a small pot with limited substrate and not much margin for error. In my last article, I talked about modern bonsai substrate, which, for the most part, is made up primarily of inorganic materials that drain well, retain moisture and are watered very frequently. It is simple and consistent, and the perfect substrate for the fertilizing regimen we need for bonsai. This is the environment that I will be talking about in this article.
If you are using a slow draining, complex (that is, too many different ingredients) and/or a high organic mix, the many variables will make it more difficult to predict how certain fertilizers will perform. You will need to be very cautious and experiment with your own soils. That is specifically why I suggest using more modern bonsai substrates –it simplifies your work and provides consistency for your valuable trees that rely on you.
On that note, if we are using a modern substrate that both allows and requires us to water frequently, then we are moving nutrients through the soil quicker. Perfect. We have a great fertilizer delivery system that gets through all the soil quickly, and doesn’t build up because we are flushing it out all the time. This means we can – and need – to fertilize a lot.
That’s a good thing, particularly in areas that have a long growing season. Our plants take up nutrients at different rates throughout the year as they are growing at different rates through the seasons. If the nutrients are always percolating through the soil, the plants can essentially “pick and choose” what nutrients they need, when they need them, and how much. Therefore, the plant always has regular access to the nutrients, but not at unhealthy levels, because we are flushing out the fertilizer salts so they do not concentrate in the inorganic substrate.
Plants generally take up the least nutrients during dormancy, which is usually in the late fall and winter for most plants, and they take up the most when new growth is surging, usually in the spring and summer months. Throughout the rest of the year, they are taking up nutrients at varying levels, the timing of which the plants know best. Therefore, it is important that we fertilize frequently, at FULL recommended levels, so that the plant has access to the nutrients it needs. With primarily inorganic substrate, we can use liquid fertilizer on Sunday, the substrate will capture it in the porous materials, and the feeder roots will begin to take it up, as needed.
Come Monday, when we water again, we begin the fertilizer diluting process, and so on throughout the week’s successive waterings. Since most of what makes up fertilizer are soluble salts, this allows them to be flushed out, so they won’t concentrate in the substrate. We can also add a time release fertilizer as a backup, which will break down and flush out faster with our frequent watering schedule. And here is the bottom line –and the big payoff– as to why modern substrate and frequent fertilizing is important for maximum health and growth – when we keep the water and the nutrients moving fast through the soil and to the roots, the PLANT “decides” what it needs at any particular time in the growing period, and it is very unlikely that you will overwater or over-fertilize. Again, we meet our goals of simplifying technical aspects of bonsai culture so we can focus on the aesthetic.
As with my discussion on soils in my last article, I’m not going to list all the fertilizer “recipes” and brands, or delve into organic verses inorganic argument, because, as with soil recipes, it’s not important. Any basic, balanced fertilizer will do. My research and personal experience has shown the following:
- Organic and inorganic fertilizers are taken up a little differently by the plant, and they both have things that the other doesn’t –I use both.
- Liquid fertilizing is a back-up for pellet fertilizer, and visa versa –I use both.
- When picking an organic fertilizer, whether pellet or liquid, use ones that include beneficial bacteria/fungi cultures and humates (humic acid) whenever possible. Humates are basically the distillation of the composting process and have been scientifically proven to enhance the plant’s metabolic process, and can be found in many organic fertilizers.
- Because we water a lot, we can use the fertilizer at the regular strength stated for any potted plant. There is no science behind the “feed at half strength” we have heard for years. If a fragile, non-woody annual veggie or houseplant can take it, so can your bonsai.
- Because we are watering a lot, we are flushing a lot, so we can feed frequently. Used at recommended levels, there is no reason why we can’t liquid fertilize at least every two weeks (I personally fertilize every week for about 35 weeks of the year), and add fine, pelletized fertilizers at the recommended levels and time periods suggested for potted plants on the fertilizer label.
My actual fertilizing regimen (in Fremont, California) is as follows:
I start liquid fertilizing in early-March with organic Grow More Seaweed Extract (0.1-0.1-1.5). Two weeks later, I use inorganic Miracle-Gro Nursery Select All Purpose fertilizer (20-20-20). Both are used at full strength, using a hose end sprayer. After that, I alternate between both, every other week, so that I am liquid fertilizing every week. This goes through October. I hit all the foliage as well, as I do EVERY time I water, on ALL my plants. Watering leaves and needles helps wash off dust and some pests, and plants do take in some of the fertilizer this way, particularly when they are stressed. Just for the sake of myth-busting, since we are on the topic of watering, foliar watering does NOT cause burn spots on Maple or other tender leaves (the drops evaporate too quick and do not focus the sun like a magnifying glass –the “sunburn from mid-day watering” myth has been scientifically debunked for years) and watering pine needles does NOT make the needles grow longer– needle length control is a function of the timing of the decandling process. Conversely, holding back fertilizer and water will not create healthy shorter needles– however, it will likely create unhealthy, stunted growth throughout the tree.
- In early April, I add Dr. Earth All Purpose Organic Fertilizer (which has humates and beneficial bacteria/fungi) at the suggested levels for potted plants. It is a fine granule that blends in, does not smell and does not attract animals. I reapply every 4 to 6 weeks throughout the growing season. This covers mid-summer growth surges and into late-summer when the plants start to redirect growth to trunks, branches and roots prior to dormancy.
- In November, I switch to a 0-10-10 fertilizer, at recommended levels, once a month through winter. This focuses nutrients for the trunk, branches and roots, not so much for use during the dormancy period itself, but rather as a store for when the plant surges the following spring.
- The regular fertilizing program begins again the following early-March
I use this regimen for all my bonsai, including “acid loving” plants. My personal opinion is that the organics and the humates (humic acid) take care of the acid “craving”, and I have no complaints from the plants, as evidenced by their health and growth.
I admit that I am relatively “aggressive” about fertilizing, and so far it has paid off. For the more squeamish, fertilizing every two or three weeks may feel more comfortable. However, my plants are lush and green, and I have found that rapid growth allows me to get more development out of a growing season. I have not personally witnessed the anecdotes I have heard about, such as plants shutting down, “burning” or having brittle spindly growth. My personal opinion, as well as the opinion of many bonsai artists, is that most bonsai enthusiasts are not fertilizing enough, to the detriment of their plants and at the cost of slow development.
So, go ahead, Seymour –“FEED” your plants! Audrey II needs to look her best for the next Bonsai show!
Copyright 2013 by Vernon Smith – All rights reserved.