By Alissa MacMillan
Q: I’ve just started gardening and someone told me about mulching, especially in this weather. It had me thinking about healthy soil and its role in the climate crisis. Is mulching important? And is there anything else I should know about the soil?
A: You’ve hit on one of the more under-researched but utterly essential aspects of climate health. “Soil is super-important in regulating global climate,” explains Dr. Richard Nair, assistant professor in plant ecology at Trinity College Dublin, soil being one of the main sites for carbon storage. “Carbon that would be held in the atmosphere otherwise is held in soil,” he says.
As Nair reminds us, plants take carbon out of the atmosphere through photosynthesis and, while plants hold some of the carbon, the majority of it is held in soils of all kinds and, “while it’s in the soil, it’s not doing anything.”
Plants are the bridge between the atmosphere above and soil below, but there are whole ecosystems underground, with micro fungi, micro fauna, and innumerable microbes, this ecosystem holding on to carbon over the long term.
But soils have their secrets: “We know a lot less about soil and below-ground parts of the ecosystem than we do about above ground,” Nair explains, mostly because “it’s a lot easier for us to see things above ground and soils are super, super complex.” What the soil itself is doing is complicated, as are the various pressures on soils, some global, some very specific to Ireland, including large amounts of nitrogen over-pollution from agriculture.
Heat and flooding also bring major risks.
“Right now we are in a heat wave and this is not something that historically happens that often but it’s likely to happen more and more frequently in the future in Ireland,” Nair says. Ireland’s soil isn’t used to being very dry, which is one concern.
“Dry soils are more likely to erode, in particular if we have a dry period and then a sudden intense rainfall,” he says, the rain washing nutrients out of the soil. The microorganisms are especially vulnerable to drought because they are so small and have a relatively short generation time.
As for plants themselves, because it was so wet earlier in the year, “everything is going crazy, apart from things like grass,” Nair says, but we’re hitting the point where drought is having a negative health effect, the plants unable to do any more photosynthesis without access to water. Many plants are “not able to grow roots into deeper parts of the earth fast enough to keep up with decreasing soil moisture.”
Soil health, which “is a bit like human health” in its complexity, “is not doing that well anywhere in the world,” he adds. The EU is currently interested, as it’s become an obvious worry, soil health being the foundation for the health of ecosystems, producing food, shelter, and all of the things we need.
On your own plot, as many gardeners know, soil health is key. To your question about mulching: yes, mulch away. “It’s really good because it helps trap water in the soil and prevents evaporation coming off the soil,” he says, and better to do it proactively rather than reactively. “In a heat wave the number one thing to do is reduce the amount of bare soil to preserve the microbes underground and keep water in the soil, which helps the plants out.”
As for watering (if there isn’t a hose-pipe ban), water deeply, Nair advises, so when it comes the day that it’s especially hot, the soil is deeply watered. But do limit the amount you water in one go, and don’t do anything that involves disturbing the soil if you can help it, like digging. You might also notice that longer grass stays greener – allow grass to be a little bit higher, as “having slightly more stuff above ground will help trap a layer of moisture in the soil.” With shorter grass, so more bare soil, more water will evaporate and it will likely leave a relatively shallow root system.
Nair also suggests holding off on fertilizing anything now, “even if you think you should. It’s much more important to let flowers cope with the drought rather than let them grow more,” so wait until it gets a bit wetter. He also suggests you try and avoid walking all over everything, as it compacts the soil, reducing its ability to hold on to water.
While soil erosion – when soil dries out and the top soil blows off – isn’t the biggest problem in Ireland, you might have some worry if you have raised beds which are disconnected from the earth.
And soil loves an organic gardener, whose focus is necessarily on the health of the ground. Organic is best for long-term soil health, in particular water retention and the support of those beneficial microbes, and for offering a stable structure with air and pore space in the soil.
“If you are farming or producing in a conventional way, where you’re not restricting the fertilizer, if you think your soil is degrading, you slap on a load of fertilizer and it’s solved in the short term.” But with properly done organic producing, you are managing the soil’s long term health and allowing it to do the things is should be doing anyway.
It might then seem like the best solution is to let the soil fend for itself, but Nair argues otherwise. “Doing nothing is not the same as doing something with intent; leaving it to take care of itself is probably not the best strategy, especially with increasing extreme events like droughts and chronic pollution, which push soil systems away from being healthy.”
And, he adds, we have passed that point. “We need to accept the fact that we live in a world that is extremely managed by humans,” he says. “We have harnessed all of the natural forces in the world that allow us to have complicated lives. We can’t just leave things like soil, which is so fundamental for life, and expect it to stay healthy and useful for us when we change so many other things.” Key to this are taking steps to better understand soil health and engaging soil policy nationally.
Because the heatwaves and floods will come. “There are going to be things like this that happen in the future,” he says, and it’s good to accept that, “as an enormously successful species, we have a bit of responsibility.”
A good place to start is with mulching.
