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How Saharan sand affects gardens in Costa Rica

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Published on Friday, June 9, 2023

By Victoria Torley

From time to time, in Costa Rica what you are taking delight in the air is filled with Saharan Air Layer (SAL) or just Saharan dust.

Despite the occasional allergic reaction, that’s a good thing because we live in a rainforest environment.

While the Amazon rainforest is the most studied, the rainforests of Costa Rica are beneficiaries of Saharan dust, just like those of the Amazon.

What is Saharan dust? We aren’t talking about just the sandy stuff here, we are talking about the dust from the Bodélé Depression in Chad. 

The depression is an ancient lake bed rich in dead microorganisms which are, in turn, rich in phosphorus, an essential element for plant growth. Add to the Bodélé dust the rest of the Saharan dust – rich in silicates, carbonates and iron – and you have the perfect mix for speeding growth in rainforests. 

A “perfect storm” of winds sweeping through narrow gaps in mountains lifts the dust in Bodélé and begins it on a journey that will take it six kilometers (about 19,700 feet) into the troposphere and waft it across the Atlantic. 

June, July and early August are the months most likely to host this SAL the air that carries the dust.

Why is it so important? Well, our tropical rains wash phosphorus and nitrogen out of the rainforest soil every year. Unless there was a source replenishing those vital nutrients, our rainforests would whither. At present, about 90% of rainforest soil is low in phosphorus which is why we add fertilizer to our garden soil.

If you’re a gardener here in Costa Rica, you know the issue. People look at our rainforests and think, “Wow, that must be rich soil!”  It isn’t.

The rainforest leaves, which often have a waxy coating to discourage predation, decay to release stored nutrients very slowly.

Growers who mow down Amazon forests to plant crops find that they deplete the soil very quickly and have to move on.

Ancient indigenous tribes were constantly composting and re-enriching the soil to maintain it and we do the same now.

Then there is the climate effect.

A year with a lot of dust storms can slow the development of hurricanes. The nutrients in the dust also provide nourishment for plankton which produce half the world’s oxygen and take up half of the world’s carbon dioxide.

It’s not all upside, though. All those tons of dust – 27 million tons to the Amazon alone – can do some damage. The dust has been linked to the death of coral in Caribbean reefs and there is that allergy thing. On the whole, however, I’m grateful for the dust storms.

Plant of the week.  It’s been a long time between orchid pictures but they are some of the most beautiful flowering plants to be found in Costa Rica, although this Coelogyne is an Asian import.  I bought this one in a pot at a feria and was told that it was a ground orchid.  Instead, it should be displayed where the long flowering stems can hang free so I will be moving it shortly.

For more information on this article or about gardening, Ms. Victoria Torley can be reached at 

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