Soft fruits in tunnels: how to plan irrigation

The root systems of raspberries and strawberries are sensitive to problems when the substrate they are cultivated in doesn’t fit their needs. When selecting your substrate for tunnel cultivation, it’s important to keep an eye on the airiness and permeability of the blend.

Airiness and structure in substrates

To reach the right air content and permeability it’s important to use materials that offer some coarseness to the mixture. In addition, when using mechanical planters, it’s relevant to make sure that the substrates are compatible with the machines.

Kekkilä Professional’s Fruit and Berry Mix (FBM) product portfolio is composed to match all the important criteria of modern strawberry and raspberry cultivation.

The FBM substrates contain high-quality raw materials like peat, moss, cotton grass, wood fibre, and perlite. Due to their high water retention, peat-based mixtures are rather forgiving when it comes to minor irrigation errors and problems. Even if something goes wrong within your irrigation cycle your soft fruit plants will still have access to some moisture, so they will not wither immediately, endangering your yield.

Irrigation of peat-based media during the growing season

In the early stages of cultivation, special attention should be paid to the amount of water used for irrigation. When using Kekkilä Professional’s FBM product line, or other peat-based growing media, we’d advise growers to start off with smaller, frequent irrigations. That way the substrate has time to absorb the water and build up a moisture buffer. Complimentary raw materials like moss make it easier for growers to wet the substrate evenly and quickly.

Root development

At the start of cultivation, the root development might be slow. It can be especially slow on the top of the pot, with bare-root plants. Water is mainly absorbed by the youngest tips of the roots. The roots need oxygen to be able to absorb water. The plant finds the oxygen within the pores between the particles within the substrate mixture. As the root system grows and the root mass increases, the need for water rises as well. This makes it even more important to use a structurally stable substrate that doesn’t compact.

Weather conditions

It’s also important to keep an eye on the temperature levels in the tunnels, as the temperature of the growing medium may affect the water uptake. In spring cultivation for example the core temperature of the substrate can drop a lot during cool nights. Although the temperature outside may appear quite warm, it takes hours for the substrate to warm up to the level of the air temperature.

Changing weather conditions during the season ask for adjustments of the irrigation strategy, as your plants will need changing amounts of water.

Plants “breathe” by exchanging gasses through small openings in their leaves. These openings are called “stomata”. If the leaves are exposed to bright lights or high air humidity, the stomata open wider, causing evaporation by the plant to increase. For the exchange of gasses to work optimally, the air in the vicinity of the stomata must neither be too dry or too humid. If plants evaporate more water, they will inevitably need more irrigation water to ensure the continuity of growth.

Water retention within the substrate is highly important when your plants are exposed to high levels of sunlight.

Calculation irrigation volumes

The amount of irrigation water required can be calculated according to the volume of substrate the plant is growing in.

Smaller irrigation volumes, like the ones you want to give at the start of cultivation, would be around 2-3% of the substrate volume. Medium irrigations amounts should be around 4-5% and large irrigation volumes should match 6-8% of the substrate volume.

Over-irrigating to fix problems

Usually, only small and medium irrigation volumes are required, but in some cases, over-irrigation may be required to equalize the humidity in different parts of the tunnels. Over-irrigating can also be used to correct a heightened EC level within the substrate. If the EC level is too high, roots won’t be able to adequately take up water.

Monitoring your irrigation

The moisture level within the substrate can be monitored with various meters. Different brands of meters use different methods and therefore give different results in moisture level. This is especially noteworthy on coarse growing media.

Read our related article:
How to check the moisture content within the substrate

to learn more about performing these checks by hand.