Wicking beds are great for growing strong, healthy plants, allowing for efficient use of water and nutrients. They comprise a water reservoir at the bottom of a container, with soil and plants on top, which are irrigated through capillary action.
UrbanVeg.com.au have installed hundreds of wicking beds in and around Sydney, and have learned many lessons along the way. While wicking beds are generally low-maintenance and productive, there are some common problems that can occur. In this article, we will discuss the most common issues with wicking beds and how to solve them.
One of the most common problems with wicking beds is poor drainage. If the water is not draining properly from the bottom of the bed, the soil can become waterlogged, leading to root rot and other issues. There are a few potential causes of poor drainage in wicking beds:
Clogged drainage holes
The drainage holes in the container can become clogged with soil or other debris, preventing water from escaping. To fix this issue, remove any soil or debris from the holes and ensure that they are clear
Improperly sized drainage holes
If the drainage holes are too small, water may not be able to escape quickly enough. Consider drilling larger holes or adding more holes to improve drainage. It is important that the liner is correctly sealed around the overflow though to eliminate leakage.
Insufficient reservoir layer
The gravel or reservoir layer at the bottom of the wicking container is essential for proper drainage. If the layer is too shallow, water may not be able to drain effectively. Aim for a layer that is at least 10cm deep. Urbanveg.com.au always use recycled plastic wicking cells in the bottom of their beds, which are fit-for-purpose and ensure a good water depth, whilst maintaining an air gap to prevent smelling.
Overfilling the water reservoir
If the water reservoir is overfilled at a faster rate that water can drain out, the bed may become saturated, giving rise to plant issues. Ensure that the water level is kept below the top of the gravel layer to prevent this issue by using a sufficient width drainage pipe that is kept unclogged.
Another potential problem with wicking beds is uneven wicking. If the soil is not evenly moist, some plants may receive too much water while others receive too little. Uneven wicking can be caused by a few factors:
Uneven soil depth
If the soil depth varies across the bed, some areas may have a longer distance to wick water from the reservoir, leading to uneven moisture levels. Ensure that the soil depth is consistent across the bed.
Uneven soil texture
If the soil texture varies across the bed, some areas may wick water more effectively than others. Aim for a consistent soil texture throughout the bed.
If the bed is not watered evenly, some areas may become too dry or too wet. Water the bed evenly and regularly to prevent this issue.
Algae growth can sometime be an issue in wicking beds. Algae can grow on the surface of the soil, preventing water from reaching the plants and competing with them for nutrients. There are a few strategies for preventing and treating algae growth:
Cover the soil
Covering the soil with mulch or a layer of stones can help to prevent algae growth by blocking out light.
Use a shade cloth
If the bed is located in a sunny area, using a shade cloth can help to reduce the amount of light that reaches the soil.
Treat with an algaecide
If algae growth is already present, treating the bed with an algaecide can help to eliminate it. Follow the instructions on the product label carefully.
Over time, salts can accumulate in the soil of wicking beds, leading to plant damage and reduced productivity. Salt build-up can occur for a few reasons:
Hard water contains high levels of dissolved minerals, such as calcium, magnesium, and potassium. These minerals can accumulate in the soil over time and lead to salt buildup. To prevent this, you can use a water softener or filter to remove the excess minerals from the water.
When you apply too much fertilizer to the soil, the excess salts from the fertilizer can build up in the soil and lead to salt build-up. It's important to follow the recommended dosage of fertilizer and avoid over-fertilizing the wicking bed.
Lack of Flushing
Flushing is the process of emptying excess salts from the soil by applying large amounts of water to the bed. If the wicking bed is not leached regularly, the salts can accumulate in the soil and lead to salt build-up. It's recommended to leach the wicking bed every few months or as needed. Often a second outlet is included near the bottom of the bed that remains closed usually, but it utilised on occasion to flush the bed out completely.
High evaporation rates
In hot and dry climates, the evaporation rate can be high, which can lead to the concentration of salts in the soil. To prevent this, you can cover the wicking bed with a layer of mulch or shade cloth to reduce the evaporation rate and maintain a more stable soil moisture level.
If the wicking bed is not designed properly or the drainage system is blocked, excess water can accumulate in the soil and lead to salt build-up. It's important to ensure that the wicking bed has good drainage and that the drainage system is functioning properly. You can also add a layer of gravel or sand to the bottom of the bed to improve drainage.
Reducing salt build-up
To address salt build-up in wicking beds, there are a few steps that you can take:
Flush the soil: Flushing the soil with water can help to remove excess salts from the bed. To do this, slowly pour water onto the soil until it begins to drain out of the bottom of the container. Repeat this process several times to flush out as much salt as possible.
Use low-salt fertilizers: Choosing fertilizers that are low in salt can help to prevent salt buildup in the soil. Look for fertilizers that have a low salt index or are specifically formulated for use in wicking beds.
Monitor soil conductivity: Regularly monitoring the electrical conductivity (EC) of the soil can help to identify when salt buildup is occurring. Aim to keep the EC below 2.0 dS/m for most plants, although some varieties may have different requirements.
Wicking Rates and Water Requirements
Understanding the wicking rates of your wicking bed can help to optimize water usage and plant growth. The wicking rate refers to the speed at which water moves from the reservoir to the soil surface. Higher wicking rates can be beneficial for plants that require more water, while lower wicking rates may be more appropriate for plants that are sensitive to overwatering.
According to a study conducted by the University of Western Australia, the wicking rates of wicking beds can vary depending on the type of soil and the height of the bed. The study found that wicking rates ranged from 4.4 mm/day for a sandy loam soil in a 200mm bed to 12.9 mm/day for a sandy loam soil in a 300mm bed.
In general, most wicking beds require watering every several weeks, depending on the climate and the water requirements of the plants. To determine when to water your wicking bed, monitor the soil moisture level regularly and water when the soil feels dry to the touch. Mulching can improve this time significantly - check out our article on mulching wicking beds.
Wicking beds are a versatile and efficient method of growing plants, but they can be prone to a few common problems. By understanding these issues and taking steps to prevent and address them, you can ensure that your wicking bed stays healthy and productive.
Some key takeaways include:
Poor drainage can be caused by clogged or improperly sized drainage holes, an insufficient gravel layer, or overfilling the water reservoir.
Uneven wicking can be caused by inconsistent soil depth or texture, or uneven watering.
Algae growth can be prevented by covering the soil, using a shade cloth, or treating with an algaecide.
Salt buildup can be prevented by using low-salt fertilizers, ensuring good drainage, and monitoring soil conductivity.
Understanding the wicking rates of your wicking bed can help to optimize water usage and plant growth.
By implementing these strategies, you can enjoy a healthy and productive wicking bed for years to come.