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Index : Container Plants & Patio Gardening
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- 14. Fertilizing Potted Plants - Top
- Potted plants are, in a sense, held captive in their containers and are totally dependent on the care we give them to survive and hopefully thrive. Besides water, the most important thing we provide these plants are the nutrients they must have to grow.
Potting soils, for the most part, are void of nutrients. Yes, it's true that some bagged soils tout the addition of nutrients, but in such minute amounts as to be essentially useless! So, don't rely on what's in the bag to grow your plants.
Fertilizer has to be supplied on a regular basis. It's especially important as the weather warms in the springtime. New growth on many plants begins in mid to late March, and sufficient nutrients, in the form of fertilizer, need to be present at this time.
Many home gardeners like using the water-soluble fertilizers such as Miracle Gro, Peters, or Shultz. These fertilizers are mild and have the advantage of not burning plants, as stronger fertilizers might. If there is a disadvantage, it comes from the fact that these quick to dissolve nutrients are also quick to leave the soil and thus must be applied frequently, usually every 2 weeks.
Becoming more and more popular are the timed-release fertilizers. They are sold in small-sized bags and bottles and container fertilizer beads coated with a plastic polymer that causes the slow, timed break down of the fertilizer into the soil. They have the advantage over water-solubles in that they feed constantly and over a longer period.
The rate of break-down of timed-release products is temperature related. For instance, if the fertilizer is advertised to feed for 3 months, that's based on temperatures in the low 70's. That works for most of the country where growing temperatures, Spring to Fall, average in the low 70's. But here in the desert, our spring temps alone can exceed 90, and with sizzling summers, these timed-release products just don't last as long. Expect them to feed for only half the amount of time indicated on the package label. If the package advertises a 4 month timed-release, plan on only 2 months here!
Timed-release fertilizers can be mixed into the soil at the time of planting, or put on the top of the soil after planting. The amount to be applied depends on the size of the container, and is listed on the product label. After evenly applying the fertilizer, scratch it into the top inch of soil. The insures an even distribution over the soil that will resist movement even when the pot is heavily watered.
As for the type of water-soluble or timed-release fertilizer to use, let the fertilizer analysis be your guide. Match it to the type or types of plants you are growing.
The fertilizer analysis tells you the comparative amounts of nitrogen, phosphorous, and potassium that are in the package. These are the 3 numbers listed prominently on the label. For instance, a product labeled 12-15-10 contains: 12 percent nitrogen, 15 percent phosphorous (phosphate) and 10 percent potassium (potash).
If your growing green-leafy plants, nitrogen is critical in their development. An absence of nitrogen results in a cessation of new growth and a yellowing of foliage. Fertilizers high in nitrogen are great for tropical foliage plants like Philodendron and Ficus. They're also excellent for other potted plants like Ivies, Pittosporum, Asparagus Ferns and other leafy plants.
If your growing plants who's interest comes from flowering or fruiting, phosphorous is critical. It stimulates flowering, fruiting and seed development. In addition, phosphorous encourages the development of new roots; especially important for young, developing plants.
Potassium, the third number on the label, is important in a number of critical plant functions. It imparts general hardiness and vigor.
For most potted plants, a balanced fertilizer with roughly equal parts of nitrogen, phosphorous, and potassium is best. The exception would be annual flowers like Petunias, Geraniums, Marigolds and others. They benefit from fertilizers higher in phosphorous, relative to nitrogen and potassium.
In addition, plants that are to be grown in pots for year-round and for multiple years benefit from fertilizers which contain additional nutrients such as: sulfur, magnesium, manganese, iron, copper, zinc, boron and molybdenum.
"Growing Citrus" will be the topic for this week's garden demonstrations. They will be presented on Wednesday at 9 a.m. at the Pima County Extension Center, 4210 N. Campbell Ave (central); and at 1 p.m. at the Wilmot Library (east), and on Friday at 1 p.m. at the Oro Valley Public Library (northwest).
The Desert Gardener on KUAT FM
Listen to my daily gardening tips, on the "Desert Gardener", on KUAT FM, 90.5 on the dial. A new gardening tip is aired every weekday at 12:11 p.m., on a variety of timely gardening and landscaping topics.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161. - Updated: March 14, 2004
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