The lush foliage and sweet fruit of the banana (Musa acuminata) are not only found in the tropics. Bananas can be grown in home gardens in U.S. Department of Agriculture plant hardiness zones 8 to 15, and can flower and produce fruit wherever they can receive 10 to 15 consecutive frost-free months. While it can require some creativity and planning to meet a banana's heat requirements in some climates, starting with soil, that meets the plant's needs lays the groundwork for a plant healthy enough to survive when temperatures dip.
While bananas can survive brief stints down to 28 degrees Fahrenheit, or may grow back from their roots if cold causes them to die back, they grow best at temperatures between 53 and 80 degrees F. Planting bananas near the house or pavement, where they benefit from reflected heat, helps keep the plant warm, but these areas can have poor soil. Bananas need rich, well-drained soil and plenty of nutrients to thrive. Feed plants monthly during warm weather with a balanced fertilizer spread 4 to 8 feet from the plant's trunk. In order for the plants to access the nutrients you so diligently apply, the soil must have the appropriate pH level.
What is pH?
This unusual looking acronym stands for "power of hydrogen." Positive and negative hydrogen ions in the soil determine how other elements, like the nitrogen, phosphorus and potassium in fertilizer, react in the soil and at what levels they are available to be taken up by plant roots. The number of positive hydrogen ions, or H+, and negative hydroxyl ions, or OH-, in the soil is expressed through a 14-point pH scale. Soil with a pH value below 7.0 has more H+ ions and is called acidic, soil with a pH above 7.0 has more OH- ions and is "alkaline." A pH of 7.0 is considered neutral. Below or above a certain level, some elements and minerals form solids that can't be absorbed by plant roots or break down and become soluble, sometimes at levels toxic to a plant. The levels at which plants thrive is their preferred pH range.
Optimal pH for Bananas
Bananas prefer a slightly acidic to neutral soil, ranging from 5.5 to 6.5 on the pH scale. Test your soil with a home pH test kit -- or send it to a soil testing laboratory for the most accurate reading -- at least a year before planting bananas. In some states your county cooperative extension service can do the test for a small fee, but in most instances they can at least recommend the most accurate home tests or direct you to a reputable testing service. Take several samples from different parts of the area where you plan to plant your bananas. Pull your samples from the root zone, not the surface of the soil. Mix all the samples together. About a pound of soil is necessary for a professional test.
Changing Soil pH
If your test results show a pH in the banana's preferred range, you can plant as soon as weather allows. If not, you aren't stuck with the soil conditions your garden presents. Just as you can add compost to moderate the consistency of a clay or sandy soil, there are amendments that can make your soil more acidic or more alkaline to better suit your bananas, but the amendments don't change your soil overnight. Raise pH -- make soil less acidic -- by adding ground limestone. Apply it in the fall before planting bananas in the spring to give the amendment time to take effect. About 5 pounds of ground limestone per 100 square feet raises pH by 1 point in loam soils. Clay requires slightly more and sandy soil less. Lowering pH, or making it less alkaline, can take one to two years. Add elemental sulfur, a powdered material, at a rate of 1 pound per 100 square feet to lower pH by 1 point, again the specific amount depends on soil type. You can decrease pH even more slowly by adding acidic organic material like shredded leaves, peat moss or pine needles into the soil.
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