March has a lot of history, hope and lore associated with it. For some superstitious folks, “Beware the Ides of March,” a quote from Shakespeare’s Julius Caesar, brings a sense of foreboding.
Searching history, you can find yourself going down the rabbit hole seeking where it all started. The Book of Esther refers to the evil Haman’s plot to destroy all Jews in the days of Moses and the Pharaoh. This occurred in mid-March. Depending on which calendar you follow, mid-March is significant in the Quar’an where Haman’s ways are mentioned several times. He was not a good guy! Mid-March is also significant in Sanatana Dharma or Hinduism of India, but the focus is light overcoming darkness.
Needless to say, it is easy to get over your head in all of this, so let’s move beyond ancient history and focus on our gardens and the arrival of spring.
For most home gardeners, it means the joy of spring is just around the corner when grass, shrubs and trees begin active growth. This means hungry plants, so it is time to fertilize.
It has been a dry winter for many parts of the Island, but in the past few weeks, some localities have had heavy rains that have leached our soils of nutrients. This makes it difficult to make general recommendations that apply to all locations. Parts of the windward side received enough precipitation to remove nutrients like nitrogen and actual topsoil as well. West Hawaii received much less but with our excessively porous rocky areas, even an inch of rain can leach important elements essential to plant growth.
Where rains in some locations leached nutrients from the soil, farms, lawns and gardens may need fertilizer now. Warming temperatures and longer days cause active growth of coffee, ornamentals, macadamia and most other plants.
Active growth requires a good supply of nutrients to assure abundant crops and healthy plants. If you have not applied fertilizer recently, now is an important time. As a general rule, new plantings should receive fertilizer every three to four months.
Established landscapes may need less depending on the condition of the soil. Where rains and irrigation are sufficient, fertilizer applied now will perk up your garden. However, where there is insufficient moisture, fertilizing will aggravate the water stress condition so hold off unless you can irrigate.
Here are some additional fertilizer tips. Be sure not to over-fertilize, nor wait too long between applications. Of course, the correct amount to use depends on the formula. The higher the formula, the less should be used.
For example, a typical 20-20-20 is much more concentrated than an 8-8-8. Another thing to note is that the fertilizer may be a slow release or a quick release type. A formula that contains the three major fertilizer elements of nitrogen, phosphorus and potassium in a 1-1-1 ratio is a common one that is sufficient for many uses.
For example, you might use a 16-16-16 or 14-14-14 or 8-8-8 for shrubs and other ornamentals. Use according to directions on the label.
For the lawn, the turf specialists usually suggest enough fertilizer to give one pound of actual nitrogen per one thousand square feet. The formulation used for grass is usually high in nitrogen such as a 21-7-14, 16-6-8, and 28-3-5. The first number in the formula represents nitrogen. This nutrient is very likely to be deficient after heavy rains. Number of applications per year depends on type and grass and soil. Centipede grass does well with 2 or 3 applications, but hybrid Bermuda may need 6 to 12 if you want a golf course quality lawn.
Don’t be confused by the vast array of fertilizer brands and formulas available. Most plants are not so specific in their nutritional needs that they can’t use and thrive on the same or similar fertilizer mixtures. The numbers represent the percent of nutrients in a bag. A mixture with a 1-1-1 ratio is very satisfactory for the majority of plants including potted houseplants.
Some folks are upset when their garden supply dealers suggest a 10-30-10, 18-5-12, 20-10-10 or some other formula than a 1-1-1 ratio fertilizer. Plants will respond about the same for 18-6-12 as they will for 16-16-16. However, the middle number, phosphorus, is sometimes locked up in certain types of soils and is not available to plants. Phosphorus is the element that encourages strong roots and cell development.
Homeowners who use lots of fertilizer containing phosphorus may over a long period of time build up too much in the soil. They would do better to use a low phosphorus fertilizer, if it has been supplied year after year in high amounts. Plants like macadamia trees and their relatives the Proteas are particularly sensitive to too much phosphorus.
A formulation high in phosphorus and potassium like 2-8-10 has less nitrogen than most other formulations and has a tendency to stimulate flowering and fruiting of many plants. This type is commonly referred to as “bloom aid” or “fruit trees special.”
When citrus fruit are puffy and dry, it is usually a sign of too much nitrogen and water. A 21-7-14 or 28-3-5 is quite high in nitrogen and has a tendency to stimulate leaf development. This type is often used on ornamental shrubs, trees and grasses. The minor elements, magnesium, zinc, and iron are also important and should be included in a good fertilization program.
Chemical fertilizers are the most readily available and are the least expensive, but if you don’t mind the cost, organic fertilizers are often a better choice. Organic and other slow release sources of nutrients seem to have added benefits, since they last longer and do not over stimulate growth that may be more susceptible to insect and disease. Organics are also beneficial to the soil micro flora and fauna.
Many ornamentals need extra applications of the minor elements, especially acid soil loving plants like ixora, hydrangea gardenia, citrus and many palms.
Royal palms, queen palms, arecas and pygmy date palms in particular need applications of magnesium, manganese, zinc and other minor elements like boron each year. Without it, bleached pale green leaves may occur. However, these minor or trace elements can be toxic if applied too heavily, so be careful and apply according to manufactures’ directions on the label.
For further information on plant nutrition and fertilizers, contact the University College of Tropical Agriculture and Human Resources Master Gardeners. In West Hawaii, call (808) 322-4893 and East Hawaii call (808) 981-5199.
Norman Bezona is professor emeritus, University of Hawaii College of Tropical Agriculture and Human Resources.
