With all the variations in rainfall this year, it is sometimes hard to know whether your garden is thirsty or overly wet.
Hawaii Island has received abundant rain this fall, with periodic dry spells in between. Where soils drain excessively, garden plants might experience stress. Heavy soils high in clay and organic matter will retain moisture longer.
In general, East Hawaii has not suffered serious drought. On the other hand, parts of West Hawaii have had good rains lately but we are heading into the dry season. There is still a restriction on water use. We must not waste water but give our landscape enough water so we don’t lose valuable trees and shrubs.
We have had several calls asking why some palms in West Hawaii appear suffering in makai landscapes. The answer seems fairly obvious if one notices the brown grass and wilted shrubs nearby. As long as we had sufficient summer and fall rains, our landscapes stayed green.
Since irrigation has been restricted, and once the rains stop, the entire region experiences drought conditions. Thus, hundreds of shrubs and trees could be on the verge of dying unless we get another drenching storm like last month.
If one considers the cost of purchasing mature palms and other trees, this is a waste of valuable landscape material. Our landscapes, when added all together, are worth millions of dollars. At a deeper more spiritual level, its almost like having pets and suddenly deciding not to give them water or food.
This might be a bit of a stretch, but there are many cultures that revere animal and plant life, so perhaps it would be a good idea to love our trees like we do our pets.
Torrential rains in some locations last month leached nutrients from the soil, so farms, lawns and gardens might need fertilizer now. These rains 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, established plantings should receive fertilizer every three to four months. Where rains and irrigation are sufficient, fertilizer applied now will perk up your garden. However, where there is insufficient moisture, fertilizing would aggravate the water stress condition, so hold off unless you can irrigate.
Here are some additional fertilizer tips.
Be sure not to overfertilize, 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 20-20-20 is much more concentrated than an 8-8-8. Another thing to note is that the fertilizer might be a slow-release type or a quick-release type.
A formula that contains the three major fertilizer elements of nitrogen, phosphorus and potash 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, turf specialists usually suggest enough fertilizer to give 1 pound of actual nitrogen per 1,000 square feet. The formulation used for grass is usually high in nitrogen, such as a 21-7-14, 16-6-8 or 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, grass and soil. Centipede grass does well with two or three applications, but hybrid Bermuda might need six 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 might, 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 is supplied year after year in high amounts. Plants such as macadamia trees and their relatives, the Proteas, are particularly sensitive to too much phosphorus.
A formulation high in phosphorus and potassium, such as 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 often is used on ornamental shrubs, trees and grasses.
The minor elements, magnesium, zinc and iron also are important and should be included in a good fertilization program.
Chemical fertilizers are the most readily available and least expensive, but if you don’t mind the cost, organic fertilizers often are a better choice.
Organic and other slow-release sources of nutrients seem to have added benefits since they last longer and do not overstimulate growth that might be more susceptible to insect and disease. Organics also are beneficial to the soil micro flora and fauna.
The soil should be moist when fertilizer is applied, and the fertilizer should be watered in immediately after application. Also, care should be taken to ensure the fertilizer material is applied over the entire root zone of the plant. Allowing clumps of fertilizer to stand in spots under the plants or against the stems might cause excessive burning.
Many ornamentals need extra applications of the minor elements, especially acidic-soil-loving plants such as ixora, 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, such as boron, each year. Without it, bleached pale green leaves might occur. However, these minor or trace elements can be toxic if applied too heavily, so be careful
Remember, take care of your garden like you would your pets, family and neighbors. Plants have feelings, too.
