Using fertilizer spikes in planters is a simple, no-mess way to feed plants, whether the planters are indoors or outside. A variety of spikes are available to provide the best combination of nutrients for different kinds of plants. Fertilizer spikes provide continuous nutrients to the roots of plants for up to two months.
Feeding All Plants
Fertilizer spikes labeled as all-purpose, indoor plant or houseplant are suitable for any kind of plant. They may contain equal amounts of nitrogen, phosphorous and potassium, stated in a ratio such as 4-4-4 or 10-10-10. Spikes with a higher percentage of nitrogen, such as spikes with a 13-4-5 or 14-3-7 ratio, promote the healthy growth and rich color of foliage. Spikes with a higher percentage of phosphorous, such as those with a 6-12-6 ratio, are formulated to encourage root growth and more flowering.
Boosting the Blooms
Plants need large amounts of phosphorous to form buds and flowers. The percentage of phosphorous in fertilizer spikes designed for flowering plants is usually equal to or more than the percentage of nitrogen. The spikes’ percentage of potassium, which promotes strong stems and roots, may be less or more than the percentages of phosphorous and nitrogen. Some examples of fertilizer ratios for flowering plants’ spikes are 3-5-6, 8-9-12 and 10-10-4.
Treating Special Plants
Orchids, including moth orchids (Phalaenopsis spp.), need a balanced fertilizer, such as 10-10-10, and manganese and molybdenum for healthy foliage and stems and large blooms. Foliage plants that do not flower, such as Boston ferns (Nephrolepis exaltata) and parlor palms (Chamaedorea elegans), need considerably more nitrogen than phosphorous and potassium.
Fertilizer spikes with a ratio of 16-2-6 provide the large amount of nitrogen foliage plants need. Moth orchids, Boston ferns and parlor palms are hardy outdoors year-round in U.S. Department of Agriculture plant hardiness zones 10 through 12 and usually are grown as houseplants in colder zones.
Using the Spikes
The number of fertilizer spikes needed is based on the size of the planter and the kind of fertilizer in the spikes. For example, a flowering plant in an 8-inch-diameter planter requires four fertilizer spikes.
Make holes in a plant’s soil, spacing those holes equally around the plant and not closer than 3 inches to the plant’s stem, and insert one fertilizer spike in each hole.
The plant’s soil should be watered thoroughly after the spikes are inserted, and a regular watering schedule should be maintained. Replace the spikes every 30 days during spring and summer, and every 60 days in fall and winter.