Maybe your winter garden looked great for a few months and is now looking tired. Maybe your well-established landscape of perennial shrubs and trees was thriving a few months ago but today seems insect- and disease-ridden. Both of these issues could be related to plant stress.
Members of the plant kingdom become stressed when they lack adequate water and nutrition. This time of year, with less cloud cover and rain, the soil dries out quickly and our plants need extra water and probably a nutritional boost.
If you did not apply mulch around your plants in the fall, it’s not too late. Though our supply of local free mulch has moved away, you can make your own or go in with some neighbors and get a load delivered from the new location near Waikoloa.
To make your own mulch, start a passive pile of pulled weeds without seeds, grass clippings, prunings and leaves. Add shredded newspaper, cardboard and wood chips, if you have them. Turn the pile a few times and it should break down into a loose mass of shredded stuff in a few months. Apply it around your plants but not directly against them. This is to avoid “burning” plant material as the breakdown process continues. In the process, the organic material will house friendly microbes that feed the soil around your plants and protect it from drying out. Applying a 3- to 4-inch mulch layer should give your plants a winter boost.
Applying compost around your plants can give them nutritional help. Composting is a great way to use garden and kitchen waste. Finished compost, called humus, is a soil amendment that is dark and rich in nutrients that your plants can readily access. Side dressing with compost, especially under a layer of mulch can greatly enhance the health of your plants and relieve them from wintertime stress.
If you use compost and mulch and regularly water plants, but they still seem listless, you could have a more serious nutritional problem requiring closer evaluation and treatment. Yellowing leaves or uncharacteristic growth patterns can be indicators of a nutritional issue. Consider purchasing a balanced fertilizer containing micronutrients, if you haven’t applied any recently. Follow the application directions.
A simple, inexpensive University of Hawaii College of Tropical Agriculture and Human Resources soil test can help you figure out what is lacking or what toxicity may be present so that you can treat appropriately. It will also tell you the pH of your soil, which can have a dramatic effect on the availability of nutrients to your plants. Call the UH CTAHR office in Kainaliu for more information and read its publication on the topic at ctahr.hawaii.edu/oc/freepubs/pdf/AS-4.pdf.
Plants, like people, respond well to attention. Walk through your garden and inspect your plants regularly and carefully. A little seasonal pruning can revitalize your landscape.
Insects can often be controlled with a blast of water, followed by an application of soap and oil. Insecticidal soap and neem oil make a good combination for routing insects, such as aphids and scale. If caterpillars are eating your leaves, apply bacillus thuringiensis. If you suspect Chinese rose beetle, go out just after sunset and collect them.
Many plant diseases prefer warm, moist environments. When conditions are dry, some diseases become dormant. Powdery mildew, however, thrives when we have dry, windy weather and leaves that get damp occasionally but dry out between waterings. This fungus can be controlled by spraying affected leaves with the following combination of products. Mix them in a gallon of water and spray late in the day to avoid hot sun exposure on newly sprayed leaves.
1 to 2 tablespoons baking soda
1 to 2 tablespoons cooking oil or a light horticultural oil
1 teaspoon liquid soap or an insecticidal soap
Hopefully these tips help enliven your garden, bring your plants back to health and make you a happy gardener.
Tropical gardening helpline
Carole asks: A few weeks ago, your column had advice on ways to encourage flowering in tuberose. You suggested using 5-10-5 fertilizer. I can’t find it anywhere. Any suggestions?
Answer: Master gardeners have suggested trying some specialty stores to see if they carry 5-10-5 fertilizer. Check with Hawaii Grower Products, hawaiigrowerproducts.com; BEI Hawaii, beihawaii.com/contact_us.php; or Ohana Greenhouse and Garden Supply, ohanagreenhouse.com/#!big-island/cz6s, to see what they carry or suggest as a substitute.
Fertilizers designed to encourage flowering usually have more phosphorus than nitrogen or potassium. That means the middle number is higher than the other two as in 5-10-5.
The first number on a fertilizer bag indicates the percentage of nitrogen in that bag. Nitrogen encourages new growth. An oversupply, however, can encourage new leaf and stem production at the expense of flowers and fruit.
The middle number tells you the percentage of phosphorus in the fertilizer. Phosphorus encourages flower and fruit production; using a fertilizer with a higher middle number will help increase blooming.
Potassium is the third number on a fertilizer bag. Potassium is good for root growth and healthy cell formation.
If you can’t find a complete fertilizer with a high middle number, fertilize your tuberose with a balanced fertilizer and simply add an extra source of phosphorus. Two organic compounds that provide slow-release phosphorus are bone meal and rock phosphate. These should be easy to find.
Although both nitrogen and potassium move in the soil, phosphorus is less mobile. It will usually stay where it is placed. Add phosphorus in the root zone of the plants when planting them or by punching holes in the soil surrounding the plant and administering phosphorus through the holes to reach the root zone.
Email plant questions to firstname.lastname@example.org for answers by certified master gardeners. Some questions will be chosen for inclusion in this column.
Diana Duff is a plant adviser, educator and consultant with an organic farm in Captain Cook.