Landscaping on the Rocks
Monroe County, which includes the Florida Keys, present some unique gardening challenges, even by Florida standards. While gardeners there have to deal with the heat, humidity, and the threat of hurricanes like the rest of the state, their location presents its own issues and opportunities.
Sense of Place
The first principle of Florida-Friendly Landscaping™ is to put the right plant in the right place. With this in mind, be aware that a plant grown in mainland landscapes may not work in the Florida Keys, including how it's planted and its maintenance. Your landscape will not succeed here unless you understand the Keys' specific climate, soil, altitude, water, and weather.
Climate
This part of the state falls into the USDA Hardiness Zone 11b, so this is a frost-free area! This opens up a number of sub-tropical and tropical plant options to gardeners in this part of the state that those of us farther north can only dream about. Over the course of a year, temperatures can drop down to lows around 41°F, with highs climbing to about 95°F.
Altitude
Beyond the temperature, there are other considerations that gardeners must take into account when selecting plants. Most are related to the area's proximity to the ocean. The altitude in the Florida Keys is anywhere from 18 feet above sea level, to right at sea level. Gardeners have to consider that plants may be subjected to salt wind spray and saltwater inundation into the root zone, storm surges, high tides, and over time, sea level rise. For locations near the shore line, or only a few feet above sea level, it's best to plant salt-tolerant plants.
Rainfall
The amount of water the area receives is another important factor to consider. The rainy/hurricane season runs from June through October, while the dry season goes from December to April. The upper Keys, closer to the mainland, receive about 40 inches a year, while the lower Keys and Key West may receive a little less, with most of that rain coming durin g the rainy season. To top it off, even during the rainy season rainfall can be sporadic.
Soil
The southern tip of Florida is made up of uplands hammock, pine lands, mangrove wetlands, and many areas with man-made fill dirt, commonly called marl. Many homeowners will have this marl in their landscape.
The soils of South Florida and the Keys are rocky, made from either old coral reefs or oolitic rock. This material tends to have poor structure, variable nutrient content, low levels of organic matter, and few beneficial microorganisms. Due to the influence of the limestone bedrock, soils are shallow and have a high pH (alkaline); they're also prone to compaction. While that is a lot to consider, what does it mean for your garden?
Having deficiencies in nutrients, organic matter, and microorganisms can potentially cause problems for your plants. In other parts of the state, a soil test would be a good starting place, but there are currently no soil tests that are effective for the Florida Keys. Even without a test, it's safe to say that enriching your soil with compost and using organic mulches can help improve the soil quality by lowering the pH and allowing more nutrients to be taken up by the plant root systems. With the Florida Keys soils being what they are, it's best to plant your acid-loving plants like hibiscus and ixora in pots.
Compaction is also an issue in the Keys. Soil particles get packed together, reducing the number and size of the spaces between the particles, leading to poor drainage and aeration, impacting roots' ability to penetrate the soil. Symptoms of soil compaction include: quality declines in ornamentals and turf, less plant growth than in other areas of the landscape, nutritional deficiency, drought stress, and roots growing above ground. Since compacted soil is slow to drain, standing water is another sign. Adding organic matter and using an auger to create small holes outside the plant drip line can help with soil compaction and the plants ability to anchor themselves.
With so many palms in South Florida, special considerations usually need to be made when selecting a fertilizer. Remember you should never use turf fertilizers within 50 feet of a palm. Instead, use "Improved palms special" 8-2-12 landscape fertilizer on turf and all ornamental plants in mixed landscapes.
Salts
Gardeners in close proximity to the ocean always have to take into consideration the role salts will play in their landscape. High levels of salt can be found in coastal soils; couple this with salty irrigation or well water, not to mention excessive fertilizer, and there's potential for some very salty soil. Leaf necrosis, plant wilt, and deficiencies in magnesium or potassium can all be caused by salinity issues.
If your landscape is 5 feet or more above sea level, you can try leaching salts out of the soil with rain and irrigation (of course, if your irrigation water is salty, this won't help). But the most effective way to deal with the persistent issue of salts is to choose salt-tolerant plants. Florida Keys native plants like mangrove, buttonwood, and Jamaican caper are the best choice.
Hurricanes
Wind and storm surge are the most destructive forces facing residents in Key West and Miami. During hurricane season (June to November), there is a 1 in 7 chance for hurricane-force winds in these areas.
When it comes to hurricane preparations for the landscape, pruning gets a lot of discussion. There is of course a right way and a wrong way to prune your trees. Over-pruning, "hurricane pruning," and topping are all examples of the wrong way to prune—these methods will ultimately end up harming your trees.
Hurricane pruning involves pruning palms so much so that only a few fronds remain, often resembling a 10 to 2 position on a clock. Palms are naturally able to withstand the high winds that hurricanes bring, so removing fronds isn't necessary. Using the same clock analogy, never remove fronds beyond the 9 to 3 position. Potassium is the most important palm nutrient and is located in the fronds--hurricane pruning robs the trees of this necessary nutrient. Topping is a method applied to other types of trees and is not an appropriate method of reducing canopy size. It uses "heading" cuts that result in decay and a weak structure. The new growth that sprouts after topping is weakly attached to the tree and can tear off during storms.
Pruning should be done well before a hurricane watch is issued and remember to always prune for good structure and strength. The benefits of pruning before hurricanes come is that new growth is light and will break way before large branches break up in a storm. Additionally, a less dense canopy may prevent trees from toppling in a storm; dense canopies will catch and hold the wind like an umbrella while a properly pruned canopy allows wind to go through the tree. Never remove more than 1/3 of the live canopy in a single pruning. When pruning remove dead, damaged, or diseased branches, water sprouts rubbing branches, branches that cross each other, suckers, and any vines that may be growing in your tree.
Our thanks to Kim Gable, Environmental Horticulture Agent with UF/IFAS Extension Monroe County for her guidance on this article.
UF/IFAS Extension Monroe County Resources
- Monroe County Lawn and Garden
- Native Palm List (PDF)
- Newcomers' Guide to Landscaping in the Florida Keys (PDF presentation)