Dave wrote:In reading some advice on raising habaneros and Scotch Bonnet peppers, I learned that these varieties of peppers have a great need for calcium and phosphorus in the soil in order to grow properly. Without enough calcium the leaves develop a wrinkled appearance. The writer strongly encourages adding a handful of bone meal to the soil on a regular basis to provide these critical nutrients. Fish emulsion or blood meal can be added as well, and the whole combination watered into the soil.
Capsaicinoid levels in peppers is partly determined by genotype, and partly by environmental factors. There's not a lot that you can do to a pepper plant to change the former; you just have to hope that you planted a variety that has the potential level of spiciness that you want. There isn't really much that you can do to make a mild genotype produce very hot fruit.
You
can mess around with the environmental factors, however, to increase or decrease whatever default level of spiciness your pepper has. The spicy capsaicinoid chemicals are first made after the flower has fully blossomed, and are produced by an enzyme called capsaicin synthase (CS) putting together various other chemicals that are floating around in the fruit. After a bit of time, a bunch of other enzymes such as peroxidase start to break down the capsaicinoids. The amount of activity shown by each of these two groups of enzymes varies over the course of the fruit's forming and ripening: the ones making capsaicinoids are more active towards the early days, the ones tearing them apart are more active later on. If you want a spicy pepper, you want to increase the ability of CS to make capsaicinoids and also decrease the ability of the enzymes that break stuff down. As a general rule, causing stress to the plant while it is forming its fruits tends to increase the concentrations of capsaicinoids.
The exact specifics of how much and when to do whatever is really hard to pinpoint, however, because different types of pepper plants have different tolerances and react in different ways. What will cause a relatively drastic change in capsaicinoid levels in one type might not have any impact on a different one, which might need more or less of whatever change you made. So the only real way to determine the best amounts of what to change to make your plants spicy is to experiment with several generations of them. If you don't have a clue as to the pedigree of your plant, then it's all going to be guesswork.
Water stress is a relatively easy way to increase concentrations of capsaicinoids in the pepper. What you do is keep the plant well watered while it is growing and blossoming. As soon as the flowers fully open, though, you water the plant as rarely as it can survive. This will probably be somewhere around once every eight or nine days. Some types of pepper can handle longer periods, some shorter. The right amount of time should result in a horribly wilted looking plant that will fully revive within four to six hours of being watered. Once you get to the point where it doesn't revive, then you'll know that you've exceeded the plant's limit. . .
This will
greatly cut back on the number of fruit that will ripen on the plant. As in, you might get a quarter of the normal yield if you are lucky. The lack of water will also hinder the ability of CS to produce capsaicinoids. The most important result, however, is that it will far more hinder the ability of the enzymes that break up the capsaicinoids. The fruits will produce the spiciness slower, but will build up greater levels of it. You'll have less peppers, but they'll be hotter.
The breaking-up enzymes will still eventually make inroads on the capsaicinoids, however, so if you let the fruits ripen too much then you'll start to lose spiciness. Again, it's a matter of trial and error to figure out just the right time to pick them. Generally, it will be somewhere around 45 days after flowering.
The presence of salicylic acid has been shown to potentially boost spiciness by increasing the amount of the building-blocks available for CS to put together into capsaicinoids, but those tests were all done with specimens of cells removed from the pepper fruit and dumped into petri dishes or whatever rather than with a whole intact plant. I have no idea of how to go about trying to add it to a growing plant with ripening fruit, or even if that would be a good idea. The closest you could get to duplicating the test conditions would be to inject the stuff straight into the epidermal cells of the interlocular septum, but that just seems like it would be kind of a weird thing to do. Perhaps you can just bury some aspirin in the soil.
On that subject: preparing the soil properly can also help, not so much in increasing spiciness but more in helping to offset the lower number of fruits that stressing the plant causes.
Red soils are usually high in iron compounds, and pepper plants don't do as well in those. Something with a lot of organic material mixed in is best. Applying the right amounts of the right fertilisers also helps, of course. With a typical N-P-K fertiliser, the nitrate part of it is the one known to be most important in making lots of flowers and fruits. A fertiliser that will have about a 15mM concentration of N in the form of urea seems to give the best results. The K is actually pretty irrelevant to pepper plants, and might even have a negative impact at anything more than low concentrations. As far as I know, nobody's done much research on the P levels, so you're on your own there. Maybe that's something that you can let the kid experiment on, and then you two can publish a paper in some scientific journal on phosphate influences on spiciness. “Inky, D. and Spawn. 2016. The Influence of Phosphate Levels on Making Bleh Peppers into Tasty Mini-Apocalypses of Spicy Doom. Journal of Culinary Catastrophes: 40-2079.”
To take up the nitrogen, though, the plants need to have the right bacteria glomped onto their roots.
Azotobacter chroococcum (I think that I got all the o's and c's in the right places there) seems to be a really good one for pepper plants. You'll need to dip the roots of the young plants into the stuff to get a good inoculation. A good root culture of that can boost your pepper harvest 250% compared to just using a bunch of chemical fertiliser.