Updated 29 January 2010!
Fertilizing! Although numerous articles are written on the subject, I find myself with the urge of sharing my experiences and understanding on the subject with fellow enthusiasts. The material written on the subject seems sparse or vague, leaving the enthusiast with more unanswered questions than anything. A favourite saying in the bonsai community is to: “Fertilize weakly, weekly”. There is no doubt this practice will provide dividends, and it is safe to do so. On the other hand during the developmental stages, many will promote feeding aggressively, more importantly, feeding with the appropriate fertilizers at the appropriate time.
I guess the proponents in each camp have their reasons, but I believe perhaps some of these practices were created or established through misinformation and/or myths, or a combination of both. Many references contain a section on fertilizers, but few engage or recommend a feeding regimen. I believe the latter is probably due to geographical locations and product availability. I further believe these references air on the side of caution, which in itself is not a bad thing. With so much information out there on the net let alone in reference material, how do we separate the “chaff from the wheat”? I believe the biggest culprit for the obscurity of this subject may have surfaced during the exponential growth of growing medium components, whilst feeding regimens remained pretty much unchanged in the last decade or so. In the last decade, we have seen growing medium composition make leaps and bounds, going from almost totally organic towards totally inert material. What did not transpire during this growth, is a proportional understanding of a feeding regimen for our trees, or better yet a thorough understanding of how feed is important to the vitality of our prized possessions, under our “current” growing conditions.
A proper program of fertilization is important for the cultivation of all types of plants, but is of particular importance when growing bonsai. There are two reasons for this. First, bonsai are grown in containers. This means there is very little space available from which the roots can obtain nutrients. Secondly, the soil mixtures traditionally used for proper bonsai cultivation are made up primarily of drainage materials (sand, rock, haydite, turface, etc.) and do not contain large amounts of organic materials that would hold onto nutrients or decompose and release nutrients into the soil.
It is therefore important to place your bonsai on a regular feeding schedule during the growing season. The plants require nutrients when they begin to grow and push buds in the early spring, and will continue to require feeding throughout the summer and into the fall (although in the fall the type of nutrients you provide will change (see below)).(Randy Clark)
As some of you know I am partial to Persiano’s “Super-feeding Program” for developing pines and conifers. To some this program is labeled as “Super-feeding” whilst others will call this program just common sense. The key to this program and its subsequent maintenance program is an extremely fast draining soil. On the latter, most folks believe their soil to be adequately fast draining, but is it? A fast draining soil is a soil in which water drains out the bottom almost as fast as it is introduced at the surface. A good potting medium is one, which will readily shed unwanted water, but retain sufficient moisture until the tree is watered once again. Some do not easily achieve this delicate balance. I believe the chief component that hinders their progress is the use of too much organic matter in their mediums, or the belief that such a component is needed.
A tree that is properly fed on a regular schedule with all the macro and micro-nutrients does not need an organic component in its potting medium to survive. All the roots need is: oxygen, water and minerals (vitamins for humans), the latter is provided with feed. Although this conversation may seem to be leading or has the appearance of heading towards totally inert growing mediums, it is not the direction I wish to take. The direction I wish to take is the requirement of our trees to get the required nourishment from their growing mediums. Even trees grown in landscapes etc… in the ground, in the earth, may or may not receive sufficient nourishment from their surroundings to sustain health. Hey, fast food restaurants will sustain life but will also lead to ones demise, in short fashion. Having said that, an organic component uses nitrogen as it decomposes, which in turn may rob the tree of this nutrient and subsequently lead to other nutrient deficiencies as well. Although a somewhat necessary component, the extensive use of this component in retaining moisture in the composition vice using a suitable inert component, should be avoided. Collin Lewis wrote, “For added water retention it is best to avoid the temptation to add more organic matter, but to reduce the aggregate particle size of the grit or, replace some of this component with one of the proprietary granular soil conditioners on the market” ((calcinated clays or similar (Turface)).
It is far better to play with the inorganic components of potting mediums vice the organic one. Organics decompose over time, and thus will no longer retain their desired original properties in the soil’s composition. The decomposition of this component will lead to soil collapse over time and limit the free exchange of oxygen between the roots and its surroundings. To further exacerbate this dilemma, the Cation Exchange Capacity (CEC) of organic components exceeds that of any inert moisture-retaining component used in our growing mediums. This large retention can lead to the accumulation of unwanted salts in our mediums, leading to the inability of the root system to take up water and nutrients. Plant cells feed by osmosis, when the accumulation of unwanted salts occurs in the container, the process is reversed. The roots can no longer take up water and nutrients; rather the cells loose their moisture and nutrients to the soil.
I believe the biggest myth that surrounds our chosen hobby is to feed at half strength. It is completely safe to feed your trees in accordance with the manufacturer's recommended dosage. Having said that, if the schedule calls for 10-10-10 and all you have available is 20-20-20, then you would indeed cut the recommended dosage in half. What you wouldn’t and shouldn’t do is to reduce 10-10-10 by half and feed twice as often than the recommended intervals. The other one is to use a balanced fertilizer, in general terms this practice is acceptable and safe to do so, until one has grasped an understanding of what the major components in fertilizers actually do, how and when playing with these ratios will benefit our trees.
I know it has been discussed before, but I believe I need to go over the basic ingredients of fertilizers in providing a better understanding of their use and the role each plays in bonsai culture. The understanding of the basic chemistry will allow us a better understanding of altering ratios of these key components as the growing season progresses right up until dormancy. The nutritive requirement of our trees varies with the seasons, and this is the key area I wish to discuss, understanding the basics will lay a platform for the reasons we may wish to alter these ratios.
Nitrogen is responsible for shoot development and foliage production, in short, for growth.
Too little nitrogen results in the plants failure to thrive and will have small possibly distorted leaves and a washed out insipid appearance. With no nitrogen at all, a large plant could die within the year. Too much nitrogen by contrast causes rapid growth, with large leaves and plump shoots that are full of water and consequently, are easy to snap.
Phosphorous is essential for the development and proper functioning of roots. It is commonly used in high concentrations for newly potted stock plants and commercial root crops. Phosphorous also encourages the fattening of woody trunks and branches. It helps establish appropriate conditions for the production of foliage and flower buds. It also enhances the resistance of plant stress and disease. Weak growth and a pale colour may be the result of an oversupply, or even a lack of phosphorous.
Potassium is the main ingredient in the production of fruit and flowers. Increasing potassium in the diet of bonsai apples and azaleas which fruit or flower poorly, will greatly improve their performance the next spring. Potassium also helps in hardening off late growth in preparation for winter. Insufficient potassium in non-flowering trees, results in winter die back. A cheap way to add potassium to the soil is to throw a few handfuls of hard wood ash onto the surface.
Now that we refreshed ourselves with the purpose of each component let’s look at the different seasons and how we can better apply each of these components to provide better dividends. In most parts fertilizing starts to late in the season. When reference material calls for resumption of feed in “early spring” this is meant to be March in the Northern Hemisphere. This original feed is like a cup of espresso after a long winter’s nap. It is meant as a quick “pick me upper”. The component ratio of this initial feed is very important.
This initial feed is normally of the following ratio 30-10-10. It is a quick nitrogen boost that is given once in the month of March for flowering & fruiting trees, evergreens, conifers and deciduous trees. It is not given to pines and I will explain later. Depending on the winter this can be carried out any time from mid month on. The exception to this rule is with pines. Pines have a very peculiar growth pattern and do not benefit from this high nitrogen boost. As a matter of fact it is strongly discouraged. With pines low nitrogen feed is recommended in spring whilst high phosphorous feed is recommended in late summer/autumn. This will encourage small needles and prolific back budding. The high phosphor administered this late in the growing season is stored for the lack of a better word and hence, the tree does not require a cup of espresso upon awakening, it is already wired for sound when spring rolls along. To provide pines with high nitrogen feed in spring will reverse what we are trying to accomplish.
This high nitrogen boost is continued during the month of April right up until the first week of May for all trees with the exception of pines and flowering/fruiting trees.
Flowering/fruiting trees receive a balanced fertilizer during the aforementioned time frame, whilst a feed high in phosphorous will prove beneficial during the growing season. The feed schedule is applied right up until the tree is in bloom and discontinued while in bloom. The regimen is resumed once the tree has finished blooming.
For pines slow release "fertilizer cakes" are sufficient in providing the necessary nutrients for health and growth. In order to keep the needle length short and promote back budding, a feed high in phosphorous is chosen during the growth period. There is a direct correlation between top and bottom growth and that is why Michael feeds the roots aggressively during the growing season.
Some proponents will recommend the discontinuation of feed during the summer months (July-August), whilst others continue during this time frame. I am with the latter camp and feed right up until mid-November. Having said that our trees are preparing for dormancy around mid-August and this is where we as enthusiast must assist them into their winter slumber. We no longer feed as aggressively and the component ratios are switched to a low nitrogen high potassium feed, to harden off our trees for winter. Regardless of the species all feed is discontinued from mid-November until the end of February.
My products of choice are produced by Plant Products. They do not endorse me, nor have I any interest on promoting their use. The reason I use these products is because they are a Canadian firm, making their products readily available in Canada. Furthermore, when this article was originally written it was aimed at a Canadian audience.
10-52-10 Known as transplant fertilizer. There are many products sold under that name at exorbitant prices. If you were to check the ingredients in transplant fertilizer, you would come to the conclusion that the ratio is 10-50-10. Because I use this product extensively, I buy it by the tub. Every tree I acquire is bare rooted. I believe as others, the sooner you can get the tree established in the proper growing medium the better. I have yet to have a failure in doing so. What I do, that is perhaps out of the norm to increase my chances of success, is that I remove the soil with a water hose vice combing out the roots. I believe that combing out the roots on nursery-acquired stock is extremely stressful to the tree not to mention the damaged caused to the fine feeder roots in the process, ridding the soil from the roots with water is gentler approach in my opinion. The roots will receive very little in form of work carried out with the exception of removing the taproot should it still be present. The tree is fed with 10-52-10 at half strength, with a repeat dose at full strength 2 weeks later. After 4 weeks, the tree is placed on a normal feeding schedule. The innocuous feed is also carried out during re-potting in spring. In this case because the trees are in good growing medium the hose is not required. Shaking the tree and gently combing the roots is all that is required to rid the tree of old soil.
This particular fertilizer ratio is also part of Persiano’s Feeding regimen as seen in the charts below.
20-20-20 As I could not get my hands on 10-10-10 I use this product at half strength.
15-30-15 “Rose or tomato” fertilizer. This fertilizer is used to feed all my flowering and fruiting trees during the season as specified in the chart below.
15-15-30 “Tomato” fertilizer is the only one I could find as a low nitrogen high potassium fertilizer to use in the fall. This fertilizer is used at 1/3 of the recommended dosage or 5-5-10.
Maxicrop manufactures the following fertilizers. The reason I chose this firm is the availability of their products in order to mimic Persiano’s recommended elements and schedule. A point to note, their fish emulsion is odourless which makes it an ideal candidate for use inside the home. Furthermore, for those who manufacture their own fertilizer cakes, the use of this particular brand of fish emulsion in the composition will not drive you out of the house.
5-1-1 Fish emulsion
0.1-1.0-0.1 Liquefied seaweed and liquefied seaweed with iron. Replaces “Roots Liquid” and “Roots liquid with iron”
0-0-3 “Pro-Tekt” is manufactured by Dyna-Grow. It is a silicon-based solution that supplies high potassium to help plants build stronger cell walls. The stronger cell walls provide a protective barrier against piercing-sucking insects and invading fungi. Applying on a regular basis will minimise or eliminate the need to use pesticides and fungicides. Additional benefits include increased stem strength, and leaf positioning of plants, which improves photosynthesis; increased heat, drought and cold tolerance, plus longer lasting leaves and blooms. Used as a supplement to provide protection against fungal and insect infestations.
Slow release “fertilizer cake” recipe
3 cups “kelp meal”
2 cups “garden lime”
1 cup “bone meal”
1 cup “blood meal”
Full strength 20-30-20 diluted with water (manufacturers recommended dosage)
1 oz fish emulsion per lb of dry ingredients. In this case 4 oz
Mix dry ingredients well. Add liquid and further mix to the consistency of oatmeal. Flour can be used as a binding agent. Place on a flat tray, score to form squares, and set out in the sun to dry. Place in a well-sealed container for future use. The mixture can also be formed into balls if one so desires.
The charts below demonstrate the use and frequency of various fertilizers during the growing season. A point to note, plant product fertilizers do contain 2% chelated iron in their formulation.
I hope I was able to shed some light into this obscure subject. This is the feeding regimen for my outdoor trees and was compiled from various sources. This feeding regimen has been in use for 3 years now and I have personally seen the benefits of such a program. As stated earlier. To some this is super-feeding, to others just a good common sense feeding program.
I was informed that Persiano's feeding regimen included a key ingredient (Roots2), which was extremely hard to come by and, definitely not available in Canada. This key ingredient if omitted would pretty much nullify any super-feeding that took place. Perhaps nullify is too strong a word in this context but, a definite reduction in efficiency would transpire. Complete article
Although it is perfectly safe to dilute fertilizers, doubling the manufacturers recommended dosage should not be carried out. The latter can be compared to many cooking recipes where doubling does not achieve the same result and thus, should be avoided at all cost.
The italicized print at the beginning of the article is an excerpt from Randy Clarks article at Knowledge of Bonsai.
Bonsai a care Manual: Colin Lewis