Water bombs and gardens: managing rainwater to combat drought
on Aug 31 2022
The climate change we are witnessing today has completely altered the rainfall patterns our plants were accustomed to. Drought deprives the green lung of our territory of a great deal of vital sap, and on those rare occasions when precipitation does arrive, it appears sudden and abundant. However, in addition to causing considerable damage, these downpours are not enough to provide our gardens with the right amount of water when they are struggling for the rest of the time.
The defining feature of this new climate, with its more tropical extreme weather events and very infrequent rainfall, is precisely months of drought, followed by all the rain arriving at once in just a few hours. Gardens, trees, plants, and especially soils are unable to absorb all the water they need in such a short time. It is therefore a good idea to make use of rainwater for irrigation by devising strategies to conserve large quantities of it within the soil itself.
Expert advice: Botanical Dry Garden techniques
The philosophy of Botanical Dry Garden is to always work in full harmony with nature, making use of its resources without damaging it. It is based on this principle that Luca Agostini, founder of the botanical garden and expert in low-water-use plants, together with his team, devised various useful strategies for making use of rainwater in the garden. What we will illustrate to you is the result of years of research and experimentation, with all techniques put into practice within the park and the gardens created and maintained by Botanical Dry Garden.
Rainwater management
What climate change is presenting us with is a fundamental problem for which a solution must be found: it rains less and less, and when it does rain, the precipitation is very abundant—downpours that we are not prepared to manage. That water, which should be made use of, is easily wasted, and once the rain stops, the garden is left dry.
This problem obviously does not only affect our gardens, but is a common dilemma across all sectors of the country. The only way to adapt to the new climatic conditions is to collect rainwater upstream and use it gradually throughout the rest of the year. Implementing strategies designed for this process is necessary not only for the country's large economies but also for small-scale operations such as our gardens.
In the past, people's concern was solely to remove excess water from their land to prevent waterlogging and root suffocation. While we used to tend to eliminate it completely, today it would be more useful to better manage this water, which arrives in an increasingly uneven manner. The right strategy is to leave it in certain areas of the garden as much as possible, so that it can slowly penetrate deep into the ground and be absorbed by the soil, instead of letting it flow directly downstream.
We are obviously talking about sloping gardens. In flat gardens, water flows slowly, already penetrating the ground, and in that case, on the contrary, it will be useful to raise the plants off the ground to avoid waterlogging problems. In sloping gardens, however, water runs off quickly, also causing significant erosion and carrying nutrients away from the soil. What can solve many of our gardens' problems and extend the life of our plants during the many weeks of drought is a more careful management of rainwater.
The three management techniques: terraces, reverse beds, and raised beds
The idea behind the first technique is the same as the terraces that were built in agriculture in the past, when the land was worked by hand or with livestock, and it was difficult to manage on slopes before the spread of powerful tractors.
Terraces make it possible to work on level ground, using contour farming, by cultivating the slope transversely and creating steps made of flat surfaces or slightly reverse slopes. An example of contour farming can be seen in our botanical garden, in the cypress area. With this technique, the flow of water downstream is slowed, reducing erosion and runoff problems.
Where there are no significant slopes, we need to create what we colloquially call reverse beds, which are level areas where water pools slightly and drains more slowly. On gently sloping land, depressions are created at intervals, where water flows slowly, penetrating these hollows. They can be planted with moisture-tolerant plants, such as oleanders, which thrive in both wet and completely dry conditions, rushes, which grow well in very wet areas, all types of reeds, and some grasses adapted to living in marshy areas. On the sides of these hollows, all types of drought-tolerant plants can be planted.
Furthermore, if the soil has a significant stony skeleton and contains large quantities of stones, these can be buried to create a water-filled chamber. This is a technique typical of rain gardens: creating raised beds. Raised beds are generally used to dispose of wastewater, but in this case, they can be used in reverse: by allowing water to flow into these underground spaces filled with air, important water reserves are created, and that water will reach greater depths, and consequently the roots of the plants.
The drainage system
However, it is also necessary to talk about the drainage system, because at some point the excess water must be drained or collected in any case. At Botanical Dry Garden, we have designed fairly invisible systems. For example, we created false walls at the boundaries of the garden, pits within which we placed very large drainage pipes, which were then covered with stones that look like the walls of ancient Etruscan or Roman cities, but are actually water channels. The result is a beautiful and distinctive landscape feature that is functional to the health of the garden and will not require major maintenance to clean the ditches, thus allowing excess water to be disposed of without causing damage. This drainage system could then channel the water into very large cisterns.
These techniques are nothing more than a small-scale application of what should also be done on a large scale. All of Italy, which is made up of rugged terrain, must make an effort during this period of change and severe drought to collect water upstream. Only collection, and then careful use throughout the year, will allow us to avoid running dry. And the same applies to our gardens, where we can begin, on our small scale, this process of conserving water resources.
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