Fertilizing

    I wish I were more of an authority on fertilizing, but I can offer only its basics, and a few important or useful concepts.
    Fertilizing is sometimes incorrectly call "feeding". One doesn't feed a plant... one supplies it with required nutrients and the plant makes its own food, feeding itself. Feel free to use the term "feed" (everyone does), but understand the difference! This is more important than just being picky about words.  This is why one shouldn't fertilize a dormant tree. A tree without leaves on it cannot make food. An evergreen in the midst of winter is not active, is not making food, and so cannot make much use of fertilizer. Likewise, a sick tree is often fertilized, thinking that is its problem, but it ends up making things worse. A sick tree is not functioning properly to begin with; adding fertilizer to the soil may interfere with water absorbtion.
    Fertilizing isn't only for inducing growth --- it's important for normal health of any tree. Most bonsai soil mixes are coarse and contain little nutrient material; fertilizing is the only source of nutrients for many bonsai.
    What to use: almost any of the widely-available fertilizer mixes are good. Always use a fairly weak concentration, say for "houseplants", and use often, perhaps weekly. This is much safer than infrequent strong fertilizings. Liquids allow you to spray the foliage directly, commonly known as "foliar feeding", which is recommended by most growers; I suppose the nutrients are more directly and quickly absorbed directly into the cells where they are used, for quicker and more efficient usage.
    Pay attention to the percentages of nitrogen, phosphate, and potassium listed on the fertilizer package. They are listed as "N-Ph-Po" on the label; for example, 15-10-5 would indicate 15% nitrogen, 10% phosphorous, and 5% potassium.
    High nitrogen encourages growth; phosphorus and potassium are important to cell structure, root development, flowering, and probably other things. Look for fertilizers that contain "trace elements" also. These are various elements and compounds that plants need in small amounts ("micronutrients"), and the addition of these help prevent a deficiency that can interfere with normal functioning of the plant's processes. (A plant with an iron deficiency, for example, will have trouble making food no matter how much nitrogen you dump on it!) You can add supplements to fertilizer mixes. "Superthrive" and various seaweed extracts are examples of supplements you can add to strictly N-Ph-Po fertilizers to enhance the mix.
    Bonsai shops sell fertilizer "cakes" which are placed on top of the soil in the pot; these give a constant, weak fertilizing at every watering. I have experimented with breaking up large tree fertilizer stakes into small chunks, and placing these on top of the soil as a cheap, handy substitute. The only problem with these is that they are usually more concentrated fertilizer and you risk "burning" the roots if you use too much or at the wrong time. I've also used the smaller, houseplant fertilizer sticks, which appear to be a little safer.
    The best time to fertilize is in the spring.  Early spring, with high-nitrogen mix for those young trees in development, where you want fast, strong growth. Late spring  (after the initial growth surge) with low-nitrogen mix for trees at a more mature stage.  Fertilizing should continue into the summer until the point at which trees go semi-dormant due to hot weather.  Fertilizing should be resumed when the weather breaks, with very low-nitrogen mixes, until the onset of fall.


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