The best way to fertilize is to have a complete soil test done first, then supplement with a fertilizer that will compensate for any nutrient deficiencies. Otherwise, a fertilizer program becomes a lot like adding fuel and oil to a car without ever checking the gas gauge or the dipstick.
Frankly, most of us aren't able or willing to take the time and effort to become soil/nutrient experts. We just want our bamboo to grow healthy and beautiful! With that in mind, I recommend a conservative approach, using the following guidelines to minimize negative impact to our environment:
- Use "organics" whenever possible. They are less likely to be over-applied, or leach nutrients into surrounding areas. Also, it's a productive way to recycle organic waste (i.e. well-composted livestock manures, recycled garden compost, recycled biosolids).
- Apply chemical fertilizers conservatively, especially if your bamboo is doing well already.
- Forget about high phosphorous/potassium fertilizers in winter to encourage root growth, unless you have a soil study in hand showing a deficiency of these two elements. For average garden soil, nitrogen is the nutrient supplement your bamboo will most likely benefit from.
- Fertilize during the growing season only. Around here, that's April 15 - October 15. After that, soils cool, light levels diminish, and plants are mostly dormant. Unused nutrients that are mobile in the soil (i.e. nitrogen) will wash out over winter. This is less a problem with well composted manures than with hot manures and most chemical fertilizers.
For bed preparation prior to planting, use a 6"-12" layer of composted "whatever" (I used horse manure, and urine-soaked shavings which I obtained free from a local stable). If you have very clay or very sandy soils, go thicker rather than thinner. Ideally, you should till the compost into the soil, but you can plant directly into well-composted manures, and still get great results.
For established plantings, apply a 3” top-dressing of composted "whatever" once per year, usually in spring before shoots emerge. Established groves create a large amount of their own leaf litter which should be left to enrich the soil and suppress weeds.
There are a multitude of fertilizers that can be used on bamboo, including granular, slow release pellets, and quick release, water soluble crystals. Regardless of the form, each will have a three-number rating that refers to the amount of nitrogen, phosphorous, and potassium (respectively) per 100 pounds of fertilizer. For example, a 100 lb. bag of 20-20-20 fertilizer would contain 20 lbs. each of nitrogen, phosphorous and potassium; these are the big 3 macronutrients most likely to cause problems if deficient in the soil, however, many fertilizers contain other macro and micro nutrients as well.
Water soluble fertilizers
may be the best choice for residential applications because they are readily available, have easy to calculate rates, and are easy to mix and apply (i.e., in a sprinkler can or garden sprayer). I have used Miracle Grow All Purpose 28-8-16 and can vouch for their claim that it won't burn if used according to directions, even in hot weather, and with new divisions. Plus, the plants seem to thrive, even in soilless mixes that do not contain any of their own nutrients. Be sure to follow the directions regarding application rates to avoid wasting and minimize environmental contamination.
Whichever fertilizer you use, fertilize early enough in the growing season that your bamboo can use up the nitrogen before going dormant in late fall. With any chemical fertilizer, be sure to follow the directions for application rates. And watch your bamboo for indicators of what it needs. If the foliage is a lush green and the plant seems vigorous, chances are it will perform well with very little or no fertilizer at all.