While raspberries need plenty of water throughout the growing season for good fruit production, the most critical stages are from bloom until harvest. The plants need approximately 1-2 inches (25-51 mm) of water per week during fruit set and development (1). If the amount of rainfall does not cover these needs, the farmer must irrigate. Otherwise, there is a high risk of small and seedy berries. During the summer months, with higher temperatures and evapotranspiration, and usually fewer rains, it is crucial to increase the frequency of irrigation (up to 2 per week) and soak the ground to a depth of 10-12 inches (254-304 mm).
Water requirements vary based on plant maturity and soil type. For example, a 100-foot (30 m) row of young plants growing in sandy loam soils needs 18 gallons (68 liters) of water daily. On the other hand, mature plants have higher needs, requiring up to 27 gallons (102 liters) of water per day. These amounts should be adjusted in heavier or sandier soils (reduced and increased, respectively). Furthermore, growers using high tunnels for raspberries will find that water requirements increase due to higher temperatures and reduced air circulation within the tunnels.
Generally, irrigation should increase in spring as new growth begins and stay consistent until fruiting is complete. Toward the end of the season, a gradual reduction in watering helps harden plants for winter. In commercial operations, observing bee activity during flowering can also provide insights, as bees are less active if irrigation creates high humidity levels, indirectly affecting pollination and, subsequently, fruit yield.
Overwatering can cause nutrient leaching, especially in sandy soils, and lead to iron chlorosis in alkaline soils. This excess water can also promote root rot, as young roots are particularly susceptible to oxygen depletion in waterlogged conditions, with some roots potentially dying within 24 hours. Using soil moisture monitoring tools, like tensiometers or electrical resistance blocks, can help growers maintain optimal soil moisture levels and prevent over-irrigation.
How to irrigate raspberries? - Choosing the Right Irrigation Method
The two main irrigation systems used in raspberries are drip (or trickle) irrigation and overhead sprinkler systems.
The overhead sprinklers are usually placed at the top of the row in the upper wire of the trellis. However, due to the higher amounts of water and the wetting of the canopy, there are problems of leaf diseases, and root and fruit rot. The farmers are advised not to use this system in raspberries. On the other hand, some experimental data showed that micro-sprinklers placed below the plant's canopy and 1.5 m (0.4 in) apart gave good results.
On the other hand, drip irrigation is the most effective method for raspberries, offering targeted water delivery that minimizes foliage wetting. This system is especially advantageous as it can be combined with fertigation, allowing for the simultaneous application of water and nutrients. Typically, drip irrigation involves placing one or two lines of drip tape per row, with emitters spaced evenly to ensure uniform water distribution along the root zone. Subsurface drip systems are especially effective for reducing evaporation and improving water use efficiency.
References
- https://www.rhs.org.uk/fruit/raspberries/grow-your-own
- https://www.extension.iastate.edu/news/2009/jun/062401.htm
- https://extension.usu.edu/yardandgarden/research/raspberry-management-for-utah
- https://extension.umn.edu/raspberry-farming/irrigation-and-nutrient-management-raspberries
- https://extension.usu.edu/files-ou/publications/publication/Horticulture_Fruit_2008-04pr.pdf
- https://extension.usu.edu/yardandgarden/research/raspberry-management-for-utah
- http://whatcom.wsu.edu/ag/edu/sfc/documents/sfc2014/Bryla_RaspberryIrrigation_SFC14.pdf
- Muster, G., & Rupp, D. (2011, June). Irrigation in raspberries-with and without fertigation. In X International Rubus and Ribes Symposium 946 (pp. 367-372).
Further reading
10 Health Benefits of Raspberries
Interesting facts about Raspberries
Raspberry Plant Information and Variety Selection
How to Cultivate Raspberries Commercially
Raspberry Soil Requirements, Site Preparation and Planting
How to Grow Raspberries from Seed
How to Grow Raspberries in Containers
Raspberries Propagation and Pollination
Raspberry Irrigation: Best Practices for Healthy Growth and High Yields
How to Train and Prune Raspberries