Soil, the bedrock of terrestrial life, is a dynamic blend of minerals, organic matter and living organisms shaped by millennia of geological and ecological processes. Nowhere is this more evident than in the unique landscape of the Florida Keys, where a delicate balance of limestone bedrock and ancient coral reefs gave rise to an ecosystem unlike any other.
The story of Keys soil begins with a chain of limestone islands, remnants of ancient coral reefs in the Upper Keys and sandbars in the Lower Keys. Over eons, sea-level fluctuations exposed these formations, allowing them to fossilize and form the distinctive limestone bedrock that underlies the region. Today, the Keys are underlain by two dominant rock formations: Key Largo limestone, which dominates above Big Pine Key, and Miami Limestone (Miami oolite), which begins in Big Pine and goes down to the Lower Keys.
So, why is there so little soil in the Florida Keys? The answer lies in the region’s relatively young geological history. While the Florida Keys have been forming for over 100,000 years, which may seem like a long time in human terms, it is relatively short in geological terms. In contrast, the nearby Appalachian Mountains, which contribute much of the parent material for Florida’s soils, are more than 480 million years old. This vast difference in geological age accounts for the scarcity of soil in the Florida Keys compared to other regions.
In the Florida Keys, soil is alkaline, with pH levels ranging from 7.2 to 8.4. This alkalinity challenges plant growth, as essential nutrients like iron, manganese, zinc and boron are often deficient. To overcome these deficiencies, gardeners must choose landscape plants suited to the natural pH of their soil. They may need to supplement with chelated iron, such as EDDHA, which is most effective at pH levels above 7.
Furthermore, incorporating compost, a nutrient-rich organic material made from decomposed plant and animal matter, can significantly enhance soil health by increasing its organic content and microbial activity. By carefully selecting plants, incorporating native plants that have evolved to withstand the unique soil pH of the region, and implementing soil amendments, gardeners can overcome the challenges of high pH soils and create vibrant, resilient landscapes in the Florida Keys.
Always test the soil before trying to adjust the pH. No adjustment is needed for home gardens and landscapes if the pH falls between 5.5 and 7.0. Most landscape plants can thrive within this range, except for “acid-loving” plants, which may require special attention. In such cases, it’s best to grow these plants in containers with tailored pH levels. Ultimately, if your plants are thriving, it’s wise to avoid unnecessary pH adjustments that could disrupt the delicate balance of the soil ecosystem.
Soil salinity is another concern in coastal areas like the Florida Keys, where salt accumulation can occur due to coastal flooding, poor-quality irrigation water or excessive fertilizer use. Managing soil salinity requires selecting salt-tolerant plants and implementing proper irrigation practices to prevent salt buildup in the soil.
Understanding the intricacies of Florida Keys soil is essential for successful gardening and landscaping in the region. By recognizing the challenges of alkaline soil and nutrient deficiencies, gardeners can make informed decisions about plant selection and soil management practices. They can unlock their landscapes’ full potential while preserving this unique ecosystem’s delicate balance. For assistance with your soil inquiries in the Florida Keys, contact the Monroe County Extension office at 305-998-9580. We can provide personalized advice and support for your gardening needs.
