Case 1: The Miracle Fruit

Behold the miracle berry, Synsepalum dulcificum. A coveted fruit in South Florida, it is best known for the "miracle" it produces when the fruit is consumed. Miraculin, the chemical contained in its fruits causes sour foods (i.e. citrus) to taste sweet. Miracle fruits are small shrubs in South Florida, often 2-4 feet in height. They are a favorite among fruit tree collectors and can easily be grown and maintained in pots. The picture above shows a healthy miracle fruit that I started from seed two months prior. The leaves are a dark green and glossy. I keep my miracle fruit seedlings in an acidic potting mixture and I fertilize them regularly with a balanced fertilizer. I was once forewarned that miracle fruit seeds often die (via "dampening off") but I've kept all of mine outside in a shade house. So far, its been a hot and very wet summer on the west coast of Florida and all three of my seedlings are doing just fine.

Now here is a picture of a not-so healthy looking Miracle fruit. It was transplanted from a garden where it was planted next to a hedge. It received partial sun and was probably fertilized at regular intervals (although that is not certain). So you might be thinking, what happened?

If you look at the other plants around this miracle fruit, you will notice the leaves are pale and yellow. if your first instinct screams, "Nitrogen," you are on to something. Most plants when deficient in nitrogen have what we call chlorotic leaves- leaves that do not produce sufficient chlorophyll (the chemical responsible for photosynthesis).  Upon closer inspection, we can also see other visual cues.

When looking for nitrogen deficiencies, there are a couple of important considerations: one, is whether the leaves are chlorotic (nitrogen deficiency begins at the tip and extends along the midrib- notice the green in the veins above), two, is it affecting older or younger leaves or both (nitrogen deficiency affects the older leaves first), and three, are there other symptoms (a nitrogen deficiency often means other nutrients can be limited). Looking at the above photo, one can see at the tips of some of the leaves, there are large red spots. If this plant was just missing nitrogen, then there wouldn't be red spots. This leads us to one of two conclusions: a) a nitrogen deficiency has also caused another ailment (i.e. another deficiency) or b) this isn't a nitrogen deficiency after all. It seems like we haven't gone far from where we started, but with all diagnoses, it is or it isn't, simple as that.

Here's what we know: miracle fruits are believed to have originated from the West coast of Africa and belong to the Family Sapotaceae. The soils of west Africa are predominantly alfisol (they have a good balance of moisture and nutrients) or oxisol (highly weathered; acidic). And luckily for us, a quick Google search will show that many fruit growers in the US have grown miracle fruit and can vouch that these plants prefer acidic soils an that they are sensitive to high levels of nutrients (over-fertilizing) and chlorine (often added to our water).

Here's what we don't know: when the last time this plant was fertilized and with what nor do we know if it was irrigated regularly with tap water (we do have water quality tests performed monthly that include chlorine). We do know that the cause of these ailments wasn't its location (partial sun was fine and it wasn't crowded), and that for the last three months its rained almost daily (salt/chlorine accumulation shouldn't be a problem if this plant was irrigated with tap water). 

Here's how we begin to tackle this problem: one, we check the soil pH. We know these plants prefer acidic soils (most likely oxisols of Africa). If the soil isn't acidic, we transplant into a potting media that is acidic or use a 50:50 mixture of perlite and sphagnum moss and we fertilize it. Two, we visually inspect the plant (including the roots)- this is both necessary and a precaution (we may find insects or root problems) and it allows us to assess the plant above and below the ground. Word of caution: if you look for problems, you're going to find them.

How to interpret the problem: use logic and connect your knowledge of soil science and plant processes to arrive at a conclusion that makes sense. For this plant, I tested the soil and found it wasn't acidic, so I already know this plant wasn't happy where it was planted originally. Secondly, I can see visually looking at the leaves, that the leaves are chlorotic. Chlorosis can be associated with a number of nutrients including nitrogen and iron, so I must try to examine for further clues. Since iron is a fixed nutrient in plant leaves, new leaves will emerge chlorotic whereas in nitrogen deficiency, younger leaves will emerge green. I inspect the plant to find all the leaves look the same. This leads me to conclude that iron is likely deficient. However, I also know that high-pH soils can cause complex deficiencies in micronutrients (including iron). I already know that this plant was in an alkaline soil so I conclude that the alkaline pH caused severe nutrient deficiencies (including the micronutrient iron).

To make things seemingly more difficult, when under severe nutrient deficiencies, plant leaves may turn red because they accumulate anthocyanin. This occurs because metabolic processes (photosynthesis) have been disrupted.  Most likely, this is what is causing the red, burnt-looking spots on the leaves, not a nutrient deficiency.

The best conclusion and recommendations we can make here are to target the most obvious problems: correct the soil pH and fertilize the plant. On the side of caution, I'd move the plant to a shade house or cover it with shade cloth to reduce the sunlight it receives while it recovers. I'd also avoid using chlorinated irrigation water (the plant did show minor visual symptoms of chlorine and/or overfertilization by displaying necrotic/dead edges on some leaves as seen below).

Although my diagnosis doesn't seem very specific, without a laboratory and with little to no budget for analyses, its a bit of a guessing game. You have to use logic to make sense when the number of possibilities seem limitless. Oftentimes, I am wrong about the specifics, but my instructions for recovery are spot on. It seems impossible because plants don't speak but knowing about their general processes, we can make educated guesses.

Till next time, happy planting!