...for the plants that is. Veronika and I have taken the past couple of days to fertilize all the plants on the grounds, using a number of different nutrient mixtures tailored to different groups of plants such as palms, grasses and banana plants. Although we don't often think of plants needing to eat, they certainly do need to, just in a way different than we are used to thinking about it. Plants use sunlight to make their own core sustenance but they also need other supplemental nutrients from their surroundings (usually from the soil) to keep them healthy. This is similar to humans needing to eat more than just sugar or white bread to live healthily. The Keys are predominantly coral stone bedrock with a thin layer of largely nutrient-poor soil, which makes it difficult to grow healthy plants, especially plants not native to the Keys, without adding rich soil and fertilizing. In addition to general fertilizing, we responded to any special nutrient deficiencies plants on the grounds were showing. It is convenient that plants will almost always show a certain type of stress in their above-ground vegetation that can help us diagnose what the plant needs before it is too late. For instance, it is likely a Thrinax is experiencing a potassium deficiency if leaves develop many light-yellow spots, so if we found this (as shown below on one of our Thrinax), we applied a potassium mix.
Unfortunately, diagnosis is not always easy and different nutrient deficiencies can look similar. Additional complications arise with plants that are picky about the amounts of nutrients they need. Hibiscus is a good example; too much nitrogen and the leaves will turn brown or "burn," yet too little and the plants will do poorly. Hibiscus is also interesting because it is often grown for its flowers, yet it does not tolerate phosphorus in levels anywhere near what is found in most bloom-enhancing fertilizer mixes. Absorption of nutrients is also dependent upon the concentration of other nutrients/ions/compounds in the soil or water. For instance, iron absorption is often inhibited by high levels of calcium in the soil or water.
Like humans, some plants make do with whatever food you give them or can live with very little, but others have much bigger appetites or specific "eating" requirements that are more difficult to accommodate, like Hibiscus. It's a little scary, but I can imagine people in the near future picking up vitamin packs much like our fertilizer packs as their main source of nutrition because of convenience and not having to eat "healthy" foods that many people would quickly do without if they could, although I personally think they are quite tasty. We really aren't that far off with people I've seen eating a donut for breakfast, but making it a "healthy" and "complete" breakfast by taking multi-vitamins with it. Yikes.