Fruitless Attempts in the Garden

Spending lots of time and money in the garden with no results?  One solution is to build raised beds, and in some instances, this may be the best approach. But before building an expensive raised bed, a little investigation and a few changes may produce the desired bountiful garden.

First, efforts need to be directed toward modifying the soil.  Here are some important considerations: 1. The pH could be too low for good growth, a common occurrence in Hawaii. In this case, an application of lime will rectify the situation.  If the pH is too high, common in many areas, sulfur or sulfur products would be advisable. 

 2. Soil nutrient levels may be deficient; common elements that may be lacking include nitrogen, potassium, phosphorous, calcium and magnesium.  These can be corrected with the addition of the proper fertilizer. Both pH imbalances and nutrient deficiencies can and should be diagnosed with a soil analysis. 

3. The soil may be contaminated by plant pathogenic fungi. In this situation, planting resistant varieties to the disease is most important. Crop rotation is another approach. See the article, "Replanted Vegetables Continue to Die" at this website.

  

Additional inquiries should include learning the proper planting dates.  Failures in the garden are occasionally caused by planting cool season vegetables such as lettuce, broccoli and cabbage in the summer, or warm season crops such as peppers and tomatoes in the winter. Moreover, the wrong varieties are often planted. Reading the publications available on the CTAHR website, http://www.ctahr.hawaii.edu/site/info.aspx, will reveal which varieties do well in Hawaii. In other areas, check the local University Cooperative Extension offices or website.

These are a handful of factors that may assist you in developing a green thumb and a lush garden.  Don’t give up! First obtain a soil analysis, then educate yourself: read about the plants you want to grow. Take gardening classes. Use the CTAHR and other Extension websites along with www.gardenguyhawaii.com 

Using Soap to Kill Insects

 Is soap good to kill insects in the garden?  

 Yes it is, in fact, gardeners have been using soaps as an insecticide since the early 1800’s.  But there are some qualifications.  An insect wears its skeleton on the outside – called an exoskeleton.  This is the hard shell we see on many insects like beetles, grasshoppers and cockroaches.  Soap will breakdown this exoskeleton, causing desiccation and thus killing the insect.  But soap has no residual affect and therefore must be sprayed directly on the pest.  Soaps will not kill insects that land on plants after they have been sprayed.

The other problem with soaps is that some plants are very sensitive to them and could exhibit some burning on the leaves - called phytotoxicity.   This is especially true if you are mixing your own concoction.  Use only a mild dishwashing soap with no additives. Purchased products are well refined and would have fewer problems with phytotoxicity.    

Here is a University of Hawai`i recipe for a good oil and soap mixture:  Make a concentrate of one tablespoon dishwashing liquid and one cup of vegetable oil.   When ready to use, shake well and mix 1 – 2 ½  teaspoons of the this mixture into one cup of water.  Spray plants thoroughly, every 5 – 7 days as needed.  Don’t spray in the heat of the day.

Why Leaves Turn Yellow

 

When the leaves of a plant begin to turn yellow, determining the cause will take some investigation. There are several possibilities:

         The first consideration is a lack of nitrogen, especially if a number of plants are affected and there has been no recent application of fertilizer.  Apply a high nitrogen fertilizer, and if after a week or so the plants begin to turn green, the problem is solved.

          If the plants don’t turn green, the problem could be a disease.  Plants can become infected with a fungus, especially when over watered, causing a root or crown rot.  Inspect the roots and the crown of the trunk.  Scratch into the bark of the trunk at the soil line and also into a piece of root.  If the tissue inside is brown or black, rather than light colored, a root or crown rot is evident.     

         Another common reason for a general yellowing is a lack of oxygen in the root zone.  This is due to too much water – over irrigation or too much rain.  As long as the soil drains well the problem is minimized.  But in clay soils, water does not drain well, resulting in a waterlogged condition.  Without adequate oxygen in the soil, roots cannot function properly, and the plant turns yellow.  If the condition continues, root rot will develop and the plant will die.  That is why so many planting instructions suggest to plant in a well-drained soil. 

         If plants are yellow and lack vigor, a soil analysis can identify nutrient deficiencies and/or a pH imbalance.  The pH reveals the acidity or alkalinity of the soil. Most plants have a definite acid/alkaline range in which they will properly grow.

         Although not common, there is always the possibility of persistent chemicals in the soil.  A soil sterilant or preemergent herbicide may have been applied to the soil.  These compounds can persist for many years.  Preemergent herbicides are those that are sprayed on the bare ground and become incorporated into the top few inches of soil.  At label dosages they affect only the target weeds and last from several months to a year.  But if an overdose is applied, the chemical will be there for many years and adversely affect many plants. 

         An infestation of microscopic round worms called nematodes (example, root knot nematode) can also cause plants to yellow and be stunted.