Using Grodan for Lettuce and Herbs

Using Grodan for Lettuce and Herbs 

In recent years there has been a worldwide increase in the consumption of lettuce and fresh herbs. Naturally this has led to an increase in production.  More and more growers are now opting to use GRODAN as their substrate.

The benefits of using GRODAN in the production process are:

• It is an inert and hygienic substrate
• The speed and uniformity of germination and growth.
• There is sufficient substrate volume to propagate to the desired plant size.
• Once it is placed in the gutter or raft system the propagation blocks provide further stability.

Inert and clean

GRODAN stone wool is an inert and hygienic substrate, so it provides your crop with a clean, disease free start. Furthermore, stone wool retains its structure throughout the cultivation cycle. Filters remain clean and free from blockages, cleaning between crops is easier and more importantly, faster, allowing less downtime between crops. The fact that it is also inert means that all applied nutrients and water are directly available for the growing crop. The combination of faster turnaround and faster growth adds to the possibility of extra cultivation cycles during the year.

Uniformity and speed of germination and growth

One of the most critical stages of cultivation is germination. Seed holes cut into the stone wool plugs provide the perfect air/water ratio around the seed which facilitates a high germination percentage. More importantly, as the stone wool substrate is uniformly saturated, each seed has the same germination environment, which provides uniformity in emergence and initial growth. The speed and uniformity of growth which follows results in a higher quality end product. It also provides a crucial opportunity for additional cultivation cycles during the year.

Substrate volume to propagate the desired plant size

There are two distinguishable stages in the production process; propagation and final production.

With the propagation of lettuce, a favorable microclimate is required. This is partly achieved by retaining a high plant density.  In GRODAN trials, we have seen that when the propagation period is extended (21-24 days), the microclimate created results in more speed in final production. Also, as larger plants are used, the production cycle is shortened, once again providing an opportunity for additional cultivation cycles during the year.

In order to extend the propagation period you also require a larger substrate volume (i.e. AO 36/40 or MM40/40). This larger volume allows more root growth and more stability.  Crucially, it also allows irrigation to be managed. Often in propagation, too much water is given. This results in weaker plants with greater susceptibility to disease. Having the right irrigation strategy with the right substrate volume will give you the possibility to be critical to the moment of irrigation. Having a precise irrigation strategy will also retain the roots within the plug and therefore result in less damage during transplanting.

To improve the irrigation strategy, we would suggest that you weigh the blocks or AO sheets to decide if irrigation is needed (table 1).

Table 1. Indicative weights to irrigate the blocks or AO sheets.
Grodan product	Approximate substrate volume	Indicative weight to base irrigation on (±60% WC)
MM 40/40	64 ml per block	40 gram per block
AO 36/40	40 ml per plug 3926ml per sheet	24 gram per plug 2.4 kg per sheet

Stability during use in gutter or raft system

Depending on the production system which is used, the GRODAN propagation component provides a certain degree of stability. For plants in gutter systems, suitable products are MM blocks or the AX plugs (figure 1). For plants in a raft system an AO plug is recommended, as its tapered base makes planting into the raft faster.

Figure 1. Left picture showing Grodan AX  plugs with basil seedlings, middle Grodan MM blocks with lettuce during propagation stage, right picture showing Grodan AO plug.

Conclusion

GRODAN stone wool will give you an inert, clean substrate which provides fast, uniform germination and growth. Whether you have a raft or gutter system, we have a plug or block that will fit your needs.

For more information contact Hort Americas at 469-532-2383 or customerservice@hortamericas.com 

Visit our corporate website at http://www.hortamericas.com