Caring for Plants

Learn how to care for the plants in your garden.

Water Conservation

by Donna Hanson

It is important that we all use common sense to conserve water. Water is supplied to the Keys through a pipe, originating from Florida City. In addition to conserving a valuable natural resource, avoiding water waste will lower your water bill.

In the home, check your water meter at a time when you are sure no water is being consumed. If the meter is running, you may have a leak. Running toilets and dripping faucets are easy repairs. Using low flow toilets and showerheads saves a lot of water. Remember that just one drop of water is a waste of 2,700 gallons per year!

Annual rainfall in the Keys is about 42 inches, with most rain occurring in the summer months. Outdoors, water can be collected in cisterns for watering plants or washing cars. Cisterns are built under homes, underground, or above ground. Also, the run-off water from window or central air conditioners can be collected and used for irrigation.

Homeowners should consider the use of what is commonly referred to as "Xeriscape" or low maintenance landscape plantings. First, consider using Florida Keys native, drought tolerant species requires less work in watering, fertilizing, and pest control, and will attract birds and butterflies to your yard. Plants native to the Keys are more adapted to the extremes of wet summer months and dry seasons during the winter. Second, group plants (native or non-native) with similar water requirements together for more efficient water use. Third, using free mulch from Monroe County will save water, time, and money.

For irrigation systems, rain sensor devices are required by Monroe County ordinance, that deactivate the system when enough rain has fallen. Also, water bedding plants and gardens with microirrigation, rather than the sprinklers used for grass. Another tip is to water early in the morning or late in the afternoon to prevent water waste through wind and heat evaporation.

Conserving water is the right thing to do, and will save you money. Encourage friends and guests to do the same!

Mulch

by Edward Bouton and Katie Davis

Mulching is a practice that has many advantages for anyone who grows plants. In simple terms, mulch is any material used to modify the soil environment. Benefits include moisture retention, weed control, and moderation of temperature changes in the soil. In addition, organic mulches help improve soil structure and provide essential plant nutrients.

Mulch can be used to cover garden beds, around trees and shrubs, in the yard in place of grass, in vegetable gardens, and on paths and driveways. The several types of mulch include organic, plastic, woven ground cloth, and rock-like materials such as gravel, pebbles and crushed stone. Each has its place, but the advantages and disadvantages of each must be considered.

Organic Mulch

Organic mulch includes pine bark, wood chips, straw, grass clippings, and shredded twigs and small branches. Any type of dry (aged) plant material, free of seed pods, can be used as mulch. Cypress mulch has been popular because of its color and longevity, but should be avoided because of the destruction of large areas of cypress swamp necessary for water conservation. Organic mulches decompose and must be renewed from time to time. As they decompose organic mulches recycle and return many essential plant micronutrients.

The recommendations for applying organic mulch around a tree or shrub are: 1) to keep it 2 inches from the stem, 2) apply in a circle 2 feet in diameter for every 1 inch of stem diameter, and 3) maintain a 2-3 inch settled depth, with repeat applications as it decomposes.

Rock Mulch

The inorganic mineral mulches such as gravel, pebbles, or crushed stone do not have all of the advantages of organic mulch and are difficult to remove once applied. Rock mulches have the disadvantages of providing easy escape for scarce water, and of reflecting solar radiation, which creates a very hot environment. Weeds are also a common problem in rock mulches. However, since they do not decompose, rock mulches do not require repeated applications. Rock mulch from native Keys sources also adds to the alkalinity of the soil and creates minor element nutritional problems for many landscape plants, especially palms.

Plastic Mulch

Plastic film, if black, is effective controlling weeds but is rather unsightly. Although plastic mulch prevents the escape of soil moisture, it also inhibits the penetration of rain and overhead irrigation water. Plastic mulch can be covered with an organic or inorganic mulch material, but because it is slippery, it is difficult to keep the other material in place. If uncovered, plastic mulch can absorb solar radiation causing high temperatures in the soil underneath, which is undesirable for plant roots.

White-on-Black Plastic Mulch

White-on-black plastic mulch is also available. This is a plastic sheet with a white top and black bottom. It provides the benefits of weed control, moisture retention, and avoids high soil temperature. However, the penetration of rain and overhead irrigation water is still prevented, and the reflection from the white surface creates a hot environment.

Ground Cloth

Woven ground cloth, whether plastic or fabric, allows air and moisture to move through, but does little to conserve soil moisture. For aesthetic purposes, it should have another mulching material on top. If an organic mulch is used on top of the ground cloth, soil moisture can be retained. Ground cloth also suppresses weeds.

Using Seaweed

by Edward Bouton

In the Keys, we have available almost unlimited rich resource for gardening. It has been estimated that there are 10,000 square kilometers of seagrass in the Gulf of Mexico and 85% of that is in the waters of Florida, primarily in Monroe County. There are few, if any, resources as valuable to gardeners for plant production on this limerock and capstone that make up Keys land. We have a seemingly endless supply, which can and should be utilized.

Turtle grass (Thalassia spp.), shoal grass (Halodule spp.), manatee grass (Syringodium spp.) and Sargassum (Sargassum spp.) are the most common seaweeds, and can be found year-round. Seaweed should be collected from areas where it has washed ashore. Do not gather living seagrass and seaweed from the waters.

Seaweed will improve the soil by increasing the organic matter and by adding nutrients essential for plant growth. Nutrient concentrations are available and vary by species, but in general, seaweed will have near neutral to slightly alkaline pH, with a nutrient value of 1.5% nitrogen, 0.1% phosphorus, and 1.3% potassium or a little higher. In addition, it will contain 5% calcium and 1.3% magnesium, plus it is a great source of essential micronutrients. Sponges are also an excellent source of plant nutrients.

Seaweed can be used in a variety of ways, such as in a compost pile, as a soil amendment after composting, or leveling low areas of fill or caprock rather than peat moss before planting. Also, seaweed works well as mulch, providing the same advantages as any other organic mulch.

Another use of seaweed is as a component of soil for vegetables or container gardening. Build a box, no bottom, about 18 inches high, and fill it with a mixture of 1/3 screened limerock, 2/3 seaweed preferably chopped, plus some synthetic slow release fertilizer. Let the soil mixture sit over the summer keeping weeds pulled, and by the fall you will have an acceptable growing medium. As the level of soil drops each year due to decomposition, more seaweed can be added. By the second year you will have a wonderful, well-aerated organic soil, high in nutrients, and perfect for growing any vegetable or other plants.

When used as mulch, fresh seaweed can be applied in a thin layer around most salt tolerant plants. But be warned- seaweed must be washed to remove salt for most uses. You can leach it in thin layers by watering for one hour per inch of seaweed, or letting the summer rain leach it for one full season. Also, it is best to chop it into small pieces using a shredder-grinder or lopping shears to hasten decomposition, and to check it for oil globs and other debris.

Composting 

by Edward Bouton and Katie Davis

Compost is the product resulting from microbial organisms decomposing organic matter (OM), resulting in a nutrient rich, dark, friable material that is ideally suited for growing plants. Compost can be incorporated into the soil, improving soil structure and water holding capacity. In addition to these physical characteristics it contains nutrients nitrogen, phosphorus, potassium, and micronutrients essential for plant growth. And soil compost can also be used as mulch around plants to moderate soil temperature and conserve water.

Plant material, paper, and food scraps (except meat and dairy products) can be used in the compost pile. Plant material includes grass clippings, leaves, seaweed that has been washed with clean water, wood chips, sawdust, twigs, and branches, but keep in mind that twigs and branches should be put through a shredder-grinder to increase the surface area before trying to compost. Remember composting depends in the action of soil organisms on the OM and the more surface area exposed the quicker the compost is produced.

Soil organisms need carbon, nitrogen, air, moisture, and heat for decomposition. Carbon is found in woody plant parts, dead leaves, and paper. Nitrogen is contained in grass trimmings, living leaves, seaweed, and food scraps. Carbon and nitrogen must both be present and in proper proportions (30:1 carbon:nitrogen). Most composting problems occur from a poor balance of carbon and nitrogen.

Moisture, air, and temperature are also important in the compost process. All can be adjusted by turning the compost. For moisture, the compost mixture should be damp, but not soaking wet. Composting occurs under aerobic conditions, so the pile should be packed, but not compacted. Temperature of the middle of the pile should be 122-131°F to kill weed seeds and plant diseases, but should not exceed 140°F or the microbial organisms will die. The temperature can be monitored by a compost pile thermometer, and used to determine when it is time to turn the pile.

There are many compost bins available through retail stores and catalogs. Home-made bins work fine also. Small amounts of compost can be made in a drum or barrel with holes cut out to allow air exchange as the barrel is rolled or turned over. For composting large amounts of OM construct a bin not less than 3 feet wide and 3 feet high. Corner posts supporting vinyl coated wire mesh makes a good compost bin. The 3 feet provides enough material so that the pile can heat properly.

When building the pile, add your carbon material and nitrogen material in alternating layers 3-4 inches thick. To insure enough nitrogen is in the mix, a handful or so of high organic nitrogen fertilizer can be added to supplement the nitrogen material if needed. Next, add enough water after each 2 layers to maintain a moist but not wet pile. Finally, add a shovel full of soil to introduce microbial organisms.

Maintenance is easy with periodic turning and mixing. To determine when the compost pile should be turned, monitor the temperature in the middle of the pile. When the pile cools to a consistent temperature, it is time to turn. In the Keys, piles are usually turned once per week. You will know when the compost is ready when turning the pile does not cause an increase in temperature. If properly built and maintained, the compost pile will produce a finished product in 6-8 weeks.

Fertilizers

by Edward Bouton, Katie Davis, and Carrie Smith

Plant nutrition requires a basic understanding of fertilizers, plant growth, irrigation, and rainfall. Controlled release fertilizers from organic matter such as grass clippings, leaves, yard trimmings, and manure are excellent sources of plant nutrients.  When these decompose, essential nutrients for growth are released.  It's the easiest, least expensive, and most environmentally sound way to fertilize. (See sections on Mulch and Composting).  You may then supplement with store-bought nutrients or fertilizer if your plants show signs of deficiency.  They are made with materials such as ammonium nitrate, superphosphate, and potassium sulfate.  They may be available in granular, liquid, or powdered form.

The Essential Elements

Plants require minerals for growth and health. The plant will not grow or complete its life cycle if any one of these nutrients is missing. The 12 minerals absorbed from the soil by the root are:

  • Macronutrients- nitrogen, phosphorus, potassium, magnesium, sulfur, and calcium
  • Micronutrients- manganese, iron, boron, copper, zinc, and molybdenum

Macronutrients are needed in larger amounts than micronutrients.

The Fertilizer Label

By law, all store-bought fertilizer, must be labeled with a guarantee of the contents. The numbers ( 10-10-10-4, for example) represent the % nitrogen, % phosphorus % potassium, and % magnesium, respectively, in the package. When comparing products, keep in mind that 20-20-20 is more concentrated than 6-6-6, and can cause fertilizer burn if over applied.

Choosing the Right Fertilizer

An important characteristic of slow-release form fertilizer is that part, or all of the nitrogen, potassium, and magnesium are provided in slow-release form. Slow-release means that the fertilizer granules dissolve over time, rather than all at once. This is especially important in the Keys because heavy rains can wash fertilizer into nearshore waters surrounding the Keys. The package often advertises slow-release, timed-release, sulfur-coated, polymer-coated or osmocoat.

If your plants show symptoms of persistent micronutrient deficiency, choose a fertilizer that contains micronutrients or simply purchase the individual nutrients.  Plants grown in alkaline or poorly aerated soil frequently show signs of iron and manganese deficiency.  Iron should be supplied in a chelated form. A chelate is a molecular structure around a metallic element that prevents the metal from becoming tied to the soil in a form unavailable to the plant. If the iron is not chelated, the plant will never benefit. One example of a good synthetic fertilizer for the Keys is “Improved Palm Special”, which can be used for all landscape plants, but any product having the described attributes is a great choice. Acid-loving plants such as Ixora, Gardenia, and Hibiscus need to have special fertilizers.  It will be an uphill battle, however, to keep them looking healthy in our high pH, alkaline soil.

Rainfall and Irrigation

A dry season normally occurs from December to May, with the rainy season from June through November. Many plants will go into a drought-induced dormancy during the dry season. The dormancy is desirable because plants do not need water. During dormancy, plants should not be fertilized or they will become stressed.

Fertilizer Amount and Frequency

The amount of fertilizer needed for a plant depends on the type of plant, plant size, growing environment, and how often the plants are fertilized during the year. For highly maintained, irrigated plants, fertilize four times per year (spring summer, winter, and fall). For plants that are rarely irrigated during the dry season, apply three times per year (late spring, summer, and fall).

In a typical year, the little rain received during February and March promotes early bloom and flush of growth, particularly on tabebuia, mango and citrus. Do not fertilize or prune at this time as both will stimulate succulent growth and will require irrigation until the June rain to prevent plant stress and pest attack. Remember that potable water is an extremely valuable resource in the Keys, so conserving it is wise.

Pruning: The Cutting Edge of Landscape Maintenance

by Elizabeth Johannsen Meadows

Snip, snip, clip, saw, buzzzzzz….familiar sounds of yard work. Proper pruning is essential to maintaining a safe and healthy home landscape. And, do not forget that pruning can be dangerous, so arm yourself with knowledge before you arm yourself with pruning tools.

Pruning is the selective removal of plant parts (usually shoots or branches) for a specific purpose. The goals of pruning are: 1) to create and shape plant form, 2) to promote plant health and longevity, and 3) to ensure the safety of people, 4) control growth, enhance flowering and fruiting. Before you take tool in hand, remember that some trees, such as mangroves, and other native trees are federally protected, and require a permit before you trim.

The two general methods of pruning are the thinning out cut and the heading back cut. The thinning out cut removes branches at their point of origin. Thinning is used to reduce the height and the spread of a plant, while retaining its natural shape. The heading back cut removes the tips of branches to a bud or node, leaving a stub. Also called pinching and tip pruning, heading back is used to train young trees and shrubs by stimulating growth of lateral shoots.

When starting a pruning job, first prune dead, diseased and damaged wood, crossing branches, and growth cluttering the center of the plant. Pruning cuts should be made at a lateral bud, crotch or trunk of plants. Cuts should be smooth and made with sterilized pruning tools. Tools can be sterilized with alcohol or diluted bleach.

Tree Pruning

When tree pruning, prune with the natural shape of the tree. When cutting limbs (thinning out cuts), be careful not to cut too close to the trunk. All tree limbs have a branch collar, which is often visible or feels like a very slight swelling. Prune just past the collar at an angle, making sure that the collar is not cut so that the tree will heal naturally. Pruning seal products are not recommended because they are not needed, and may actually harm the tree by trapping disease into fresh cuts. This situation may be more inviting to wood rotting organisms than one with no wound cover. However, treatment with a fungicide may be beneficial.  Also, be aware that different trees should be pruned at different times of the year, depending on when they flower and whether flowering occurs on the current or previous season's growth. Structural pruning and light pruning can be done anytime. However, no more than 20-30% of the canopy should be removed in one year.

Other types of tree pruning include crown raising cuts and drop crotch pruning. Crown raising cuts are cuts that remove lower branches. This is usually done to increase visibility under a tree for traffic or safety purposes. Drop crotch pruning reduces the length of the main branch by cutting it just above a lateral branch that is large enough to assume the role of leader. This is only done in cases where the original leader goes through power lines. (Planting trees under power lines should be avoided.) Never top or hatrack a tree: this is heading back all the branches to an indiscriminate height.

Palm Pruning

When pruning palm trees, prune only dead fronds. Prematurely cutting palm fronds, often referred to as “hurricane” or “feather-tip” pruning starves the tree, and causes chemicals that attract insects to be released from the palm. In addition, excessive pruning causes the trunk to constrict, creating an ugly pucker and weakening the trunk that ultimately causes the trunk to snap at the weak point.

Shrub Pruning

Shrubs are pruned by either heading back or thinning. Shrubs pruned as a solid hedge should be trimmed so that the base of the hedge is slightly wider than the top. This ensures maximum light exposure for the lower leaves; otherwise, the top of the hedge casts a shadow on the bottom leaves, which then fall off due to lack of light.

Safety

Lastly, and most importantly, a few words on safety. Wear protective eyewear and gloves. Do not work alone. Never trim a tree near a power line; call the electric company to prune or call a certified arborist. If a ladder or chainsaw is required, call a professional certified arborist.  Sterilize cutting equipment after each use to prevent spread of diseases.