This past winter and spring, more rainfall has been recorded than in previous years. This has posed significant challenges for many tree nurseries and existing green spaces, such as city parks and gardens. Overflowing waterways and saturated soils are not just a temporary inconvenience; they have long-lasting effects on the health and growth of trees and plants.

Saturated soil: an invisible enemy

One of the biggest problems resulting from extreme rainfall is soil saturation. When the soil is fully saturated with water, it can lead to several negative effects. A healthy soil contains enough tiny air pockets around the plant roots to prevent suffocation. Suffocation can lead to root rot, a condition that can spread quickly and significantly impact the growth and health of trees.

Additionally, saturated soil can lead to subsidence. When the soil absorbs too much water, it becomes heavy and compact. This not only reduces the soil’s porosity but can also endanger the stability of trees. Shallow-rooted trees and plants, as well as young saplings, are at the greatest risk of falling over due to insufficient anchoring.

Root rot and delayed growth: major impact for tree nurseries

For tree nurseries, root rot is one of the most feared consequences of a wet period. This fungal disease, known as Phytophthora, thrives in wet conditions and can quickly infect an entire nursery. Affected trees show symptoms such as wilting, discoloration of leaves, and in severe cases, the death of a tree.

Moreover, soil saturation causes delayed growth. Trees and plants need a good balance of water and air in the soil to grow optimally. Excessive water disrupts this balance, preventing roots from functioning properly, resulting in slower growth and reduced vitality. This means growers have to wait longer for marketable trees, which incurs additional costs. The financial impact on businesses is substantial.

Effects on city parks and gardens

Tree nurseries are not the only to suffer from excessive rainfall. It impacts existing green spaces, such as city parks and gardens, as well. In urban areas, where the soil is often already compacted due to construction and human activity, extra water can lead to serious problems. The soil is so compacted that water drains away with difficulty, quickly causing water saturation. As a result, plants and grass fields stand with their roots in water for too long, effectively drowning. Bare spots and dying vegetation are the visible consequences. Municipalities and park managers must take extra measures to mitigate damage and carry out restoration work, such as improving drainage and replacing damaged plants. This does not come cheaply.

Resilient soil is essential

Given the expectation of more extreme weather conditions in the future, having a resilient soil is crucial. A resilient soil is characterised by a healthy structure with both good water retention and good drainage. It also contains sufficient biodiversity above and below the surface. All these factors contribute to better handling of excess water and maintaining soil structure.

To prevent waterlogging, tree nurseries can invest in drainage systems that quickly and efficiently remove excess water. These can range from underground pipes to ditches that carry water away from the root zone. Another preventative measure is the creation of raised plant beds, which usually have good aeration, ensuring the plant roots continue to access oxygen.

Organic layers and innovative soil solutions

To address the effects of heavy rainfall in the future, two key components need to be considered. The first is improving the soil’s buffering capacity. This requires maintaining and increasing the organic matter content in the soil. Adding organic materials like compost and mulch can improve soil structure and its ability to retain water. Organic matter promotes healthy soil fauna, which in turn enhances aeration and drainage. These layers are vital for the water system and play a significant role in providing nutrients for the growth of trees and plants.

Additionally, professionals are looking ahead and adapting to changing climatic conditions by investing heavily in soil improvement. Using advanced and innovative technologies such as soil moisture sensors can help growers obtain real-time information about soil moisture levels, preventing the soil from drying out so much during droughts that water runs off rather than soaking in.

Targeted research: innovation in practice

An example of a successful adaptation is a nursery that, after several wet seasons, invested in an advanced drainage system combined with sensor technology. By using soil moisture sensors, they now have precise insights into when the soil is becoming saturated. This allows the grower to activate the drainage system early to remove excess water. This approach has significantly reduced root rot and improved growth results. An additional benefit is the reduced incidence of diseases and pests.

What should nurseries and green space managers do?

The extremely wet winter of 2023/2024 has exposed the vulnerability of our soils and green spaces. For tree nurseries and green space managers, it remains crucial to take proactive steps to make their soils more resilient. Investing in good drainage, organic layers, and innovative technologies will help mitigate the impact of future water challenges. Only by taking measures now, can we ensure that our trees and plants remain healthy and that our green spaces will flourish, regardless of weather conditions. The challenges are significant, but with the right approach and dedication, tree nurseries and green space managers can help build a sustainable future where both trees and people can thrive.

Experiences from GrootGroenPlus participant Laurens van Haperen of the conifer and shrub nursery from Wagenberg.

Laurens: “After two consecutive wet winters, the effects are clearly visible on our fields. Chamaecyparis species, in particular, have suffered.” We asked Laurens if he was able to remedy this.

Laurens: “Intervening during cultivation is difficult, so we try to optimise conditions before planting by growing cover crops, levelling the ground in summer (levelling is fine-grinding ploughed ground and levelling the land to ensure good water drainage), digging drainage ditches, and adding extra organic material. Maintaining the topsoil, where most root formation occurs, is crucial. We notice that water does not drain away in some parts of the field, which affects soil structure and negatively impacts soil life due to a lack of oxygen. This leads to poorly developed crops due to reduced rooting during the growing season.”

We asked if good drainage would be the solution. Laurens: “We increasingly more often consider installing controlled drainage to regulate water levels in winter and summer. The use of measuring instruments offers great advantages, because moisture measurements allow for more targeted actions. This reduces ‘cultivating by feel’ and can be well substantiated with a pF curve. In conclusion, we believe the green industry must take proactive steps. Soil resilience is essential, and everyone can contribute to better soil quality in their own way.”

We also posed these questions to Huib den Dunnen of the H. den Dunnen field nursery of ornamental shrubs in Zundert.

Huib: “Let me start by saying that we have never dealt with so much water as we did last season. On our field nursery, where we grow challenging deciduous ornamental shrubs with root balls, it has been a significant challenge to get everything through this wet season properly. Overall, this has gone reasonably well because we take several measures prior to each cultivation.”

What measures have you taken? Huib: “Our plot is drained and lies quite high relative to the main brook in Zundert, where the water eventually flows to. For each crop, we re-grade everything to a slope and thoroughly loosen the subsoil. The use of compost is also starting to pay off. Additionally, growing on beds is a great advantage during such a wet winter. Excessive rain can also flow off the land via the paths. To prevent all the water from immediately flowing into the ditch, we sow a wide grass lane that also serves as a path. We also do not bring heavy machinery onto the land during cultivation, keeping the beds nicely airy.”

All’s well that end’s well? “In hindsight, it is easy to talk, and we have also worried about whether everything would survive, but when we look at the crops that are to be delivered this year, we see good crop development.”

The KwekersBode also asked the Water work group of the Coöperatieve vereniging Treeport for a response:

“The topic of water has two aspects for us: quality and quantity. We have been working on quality for years with the Brabantse Delta Water Board (WSBD, waterschap Brabantse Delta). The project ‘Schoon Water voor Brabant’ (clean water for Brabant), that we have created together, has allowed us to make great strides in improving water quality. We also work closely with WSBD on the quantity issue. They help us manage excess water, but they also understand and recognise the water demand for our crops. A common comment this winter was, ‘It’s not unlikely that we will be begging for water in four weeks.’ This illustrates how difficult it will be to adapt the entire water system for the future. Fortunately, Treeport has many members willing to share their knowledge and invest their time.” 

On behalf of trade fair GrootGroenPlus: David Bömer, Chairman

“Water is crucial for the nursery stock industry in many ways. It is therefore good to see that several specialists with knowledge of both quality and quantity are present at the trade floor. Their expertise is as welcome as a refreshing glass of water on a sunny day!”