by Renato Ferretti

The establishment of a container plant nursery requires a hydraulic-agrarian arrangement that makes it possible to achieve the following objectives:

• availability of water for irrigation;

• possibility to drain away excess rainwater and irrigation water;

• prevention of weed growth;

• creation of a microclimate conducive to plant growth;

• recycling water for use in multiple production cycles;

• easy accessibility to means of transport without damaging the soil.

The cultivation area serves as the “soil base” in which container plants remain for a certain period of time, usually not less than one vegetative cycle.

We have seen that in order to facilitate container cultivation and allow for proper use of the soil, the latter must be prepared through various methods, some of which can be expensive, in contradiction to each other, and not always fully sustainable.

Covering the soil with black polyethylene sheeting is suitable for planting systems involving the recycling of infiltration water but it certainly does not ensure an efficient hydrological balance. With this method, the soil is levelled, arranged with an appropriate slope and covered with black polyethylene sheeting, which is held in place by concrete slabs placed in regularly spaced parallel rows. The polyethylene sheeting can also be secured by burying it at the edges of the plots. The lifespan of this covering depends on the thickness and characteristics of the black polyethylene and normally does not exceed four-five years.

Recently, the application of this method has decreased due to its drawbacks, such as short lifespan, possible tears during cultivation operations, and water stagnation. Moreover, being impermeable, it does not allow gas and water exchanges between air and soil, which is a significantly negative aspect for the agroecosystem and the potential reconversion to open field crops.

The need to avoid the disadvantages associated with the use of black polyethylene alone and to create systems that will maintain the hydrological balance has led to the development of cultivation areas using draining materials such as gravel, expanded clay, crushed stones, etc.

In this case, too, the plots must be levelled, providing the required slope for proper drainage of excess waters. The prepared soil is then covered with non-woven fabric followed by a layer of draining materials about 10cm deep. Although this system improves the agronomic conditions of the crop, it clearly has a heavy impact on the agricultural soil, making it difficult to reuse for its original purpose.

Agricultural land is a precious asset that must be protected, especially in the most fertile areas, such as those typically dedicated to ornamental horticulture. Therefore, the choice of soil cover must take this into account, using materials permeable to water and air so that the soil can perform its functions while at the same time preventing weed growth and allowing for future use of the land as an agronomic basis for cultivation. By replacing the black polyethylene film with an anti-algae mulching fabric, which is semi-permeable, the negative effects mentioned above are significantly reduced.

Plants in medium and large volume containers (from 25 to 100 litres) are placed directly on the levelled soil without any covering material. This is a simple and cost-effective solution that in some areas, such as in Angers in France, is also used for cultivation in smaller containers. Another alternative is vegetative mulching, which could reduce the negative effects of fixed covers on the soil, being highly effective in terms of protection against weeds and drainage from the container.

Container plants with a height exceeding 100-150 cm need special supports to prevent the wind from blowing them over. The anchoring systems can be of different types:

• anchoring each plant to a metal or plastic wire stretched between wooden/iron stakes or concrete supports. This system is suitable for medium and large-sized plants.
• tying the young plant to a thin rod (often made of coloured plastic) measuring 80-120 cm in in length, placed in the container. This system is more flexible than the previous one in terms of moving the plants within the cultivation area.

Small-sized plants are cultivated in pots that are placed closely together, while larger plants or those with a broad canopy are positioned individually at a certain distance from each other. As is to be expected, plants in the cultivation area are arranged according to species and container size, so as to have homogeneous cultivation sectors in the area.

Generally, plants are grouped into homogeneous sectors based on variety and container volume. For part of the production, some nurseries adopt the intercropping of various species with different vegetative habitus and special light requirements. For example, in the tall tree sector, shade loving shrubs in containers are placed in between the trees in the row. These solutions stem mostly from the need to make full use of the surface area destined to container cultivation, a surface area that requires significant investments in land. This also justifies the high degree of cultivation intensity typical of this cultivation system.