Hydroponic Onions: A Complete Guide to Growing Onions in Water

Have you ever considered growing onions without soil? It might sound unconventional, but cultivating onions in water, a process known as hydroponics, is a surprisingly feasible and rewarding endeavor. Hydroponics offers numerous advantages, including faster growth, reduced risk of soilborne diseases, and the ability to grow onions indoors regardless of the season. This comprehensive guide will walk you through every step of successfully growing onions in water, from selecting the right variety to troubleshooting common issues.

Why Grow Onions in Water?

Before we delve into the specifics, let’s explore why you might choose hydroponics over traditional soil-based gardening:

• Faster Growth: In a well-managed hydroponic system, onions often grow faster than those planted in soil. Nutrients are directly accessible to the roots, eliminating the need for them to search through the soil.
• Reduced Pest and Disease Issues: Without soil, you drastically reduce the chances of soilborne pests and diseases affecting your onions.
• Indoor Growing: Hydroponics allows you to grow onions indoors year-round, irrespective of weather conditions or space limitations.
• Space Efficiency: You can grow a significant number of onions in a relatively small space using hydroponic methods.
• Control Over Nutrients: You have precise control over the nutrients your onions receive, ensuring they get the perfect balance for optimal growth.
• Less Mess: Say goodbye to digging in the dirt! Hydroponics is generally a cleaner gardening method.

Types of Hydroponic Systems Suitable for Onions

Several hydroponic methods can successfully grow onions, but some are more practical and beginner-friendly than others. Here are a few commonly used systems:

• Deep Water Culture (DWC): This is a simple and popular method where plant roots are suspended in an aerated nutrient solution. DWC is well-suited for onions, especially bulb onions.
• Nutrient Film Technique (NFT): This method involves a thin film of nutrient solution constantly flowing over the roots. NFT is good for leafy vegetables and smaller bulb varieties but might not be the best for large bulb onions, especially as they mature.
• Kratky Method: A passive hydroponic method where the plant’s roots are suspended in a non-circulating nutrient solution. It’s great for beginners as it requires minimal setup and maintenance. Onions can be grown this way with good results.
• Aeroponics: Here, plant roots are suspended in the air and periodically sprayed with nutrient-rich water. While effective, aeroponics systems can be more complex to set up and maintain and are not generally recommended for beginners growing onions.

For this guide, we will focus primarily on the Deep Water Culture (DWC) and the Kratky method, as they are generally easier to implement, especially for beginners.

Step-by-Step Guide to Growing Onions in Water

Let’s get into the details of growing hydroponic onions using the DWC and Kratky methods:

Materials You’ll Need

Before we begin, gather these essential materials:

• Onion Sets or Seedlings: You can start with onion sets (small, immature bulbs) or seedlings grown from seeds. Sets are generally easier for beginners. You will need to get the onion from the local garden supply. Red, white or yellow varieties work.
• Hydroponic Container: A food-grade bucket (5-gallon works well), a wide-mouth jar or a large plastic storage container with lid, depending on your system (DWC or Kratky).
• Net Pots: These are small, plastic pots with mesh sides that will hold the onion bulb or seedlings.
• Growing Medium: For the net pots, you will need an inert medium like coco coir, perlite or LECA (lightweight expanded clay aggregate). Do not use soil.
• Hydroponic Nutrient Solution: A balanced solution specifically formulated for leafy or general vegetable growth. This product should be store bought and have directions on the packaging for dilution rates.
• Air Pump and Air Stone (for DWC): These will provide essential aeration to the nutrient solution. This is not required if using the Kratky method.
• pH Testing Kit: To monitor and adjust the pH of the nutrient solution.
• Water: Use clean, non-chlorinated water (tap water is fine if allowed to sit for 24 hours to allow the chlorine to evaporate, or you can use filtered water).
• Optional: Grow lights, if you are growing indoors with limited natural light.

Step-by-Step Instructions for DWC (Deep Water Culture)

1. Prepare the Container: If using a bucket, drill holes in the lid to accommodate your net pots. Ensure the net pots will be suspended above the bottom of the container, allowing the roots to reach the nutrient solution.
2. Set Up the Air Pump and Air Stone: Place the air stone at the bottom of the container. Connect it to the air pump using the tubing. The air stone will be completely submerged in water, so ensure all connections are tight and watertight.
3. Prepare the Growing Medium: Pre-soak your coco coir, LECA or perlite before filling your net pots. Then fill the net pots with your chosen medium.
4. Plant the Onions: If using onion sets, place one set in the center of each net pot, ensuring the bottom of the bulb is slightly submerged into the growing medium, with the top of the set exposed. If using seedlings, carefully transplant them into the net pots, gently covering the roots with the growing medium.
5. Prepare the Nutrient Solution: Mix the hydroponic nutrient solution according to the manufacturer’s instructions. Add water to the container until it almost reaches the bottom of the net pots.
6. Place the Net Pots into the Container: Suspend the net pots in the holes on the lid, ensuring the bottom of the net pots are barely touching the water, or the roots if using a seedling. This will allow the water to wick up into the medium, keeping it damp for root growth.
7. Adjust pH: Use your pH testing kit to check the pH of the nutrient solution. Aim for a pH between 6.0 and 6.5 for onions. Adjust the pH using pH up or pH down solutions as needed.
8. Turn on the Air Pump: Make sure the air pump is working and you can see bubbles forming from the air stone.
9. Provide Adequate Light: Place your hydroponic system in a location where it will receive at least 6-8 hours of sunlight daily. If growing indoors with limited natural light, supplement with grow lights. A T5 grow light, or an LED grow light, both of which are relatively inexpensive, are good choices for indoor growing.
10. Monitor and Maintain: Regularly check the nutrient solution level and top it up as needed. Monitor the pH and adjust as necessary. Change the nutrient solution every 1-2 weeks to prevent nutrient imbalances.

Step-by-Step Instructions for the Kratky Method

1. Prepare the Container: Use an opaque container to prevent algae growth. Make holes in the lid to accommodate your net pots.
2. Prepare the Growing Medium: Pre-soak your coco coir, LECA, or perlite before filling your net pots.
3. Plant the Onions: If using onion sets, place one set in the center of each net pot, ensuring the bottom of the bulb is slightly submerged into the growing medium, with the top of the set exposed. If using seedlings, carefully transplant them into the net pots, gently covering the roots with the growing medium.
4. Prepare the Nutrient Solution: Mix the hydroponic nutrient solution according to the manufacturer’s instructions. Fill the container with nutrient solution so the water line will be about halfway up the net pot.
5. Place the Net Pots into the Container: Suspend the net pots in the holes on the lid. The bottom of the net pots will be partially submerged in the nutrient solution, allowing the water to wick up into the growing medium.
6. Adjust pH: Use your pH testing kit to check the pH of the nutrient solution. Aim for a pH between 6.0 and 6.5 for onions. Adjust the pH using pH up or pH down solutions as needed.
7. Provide Adequate Light: Place your hydroponic system in a location where it will receive at least 6-8 hours of sunlight daily. If growing indoors with limited natural light, supplement with grow lights.
8. Monitor and Maintain: Regularly check the nutrient solution level and top it up as needed. Monitor the pH and adjust as necessary. Since this is a passive system, you will change the entire solution every 2-3 weeks, or when it gets low.

Caring for Your Hydroponic Onions

Successful hydroponic onion growing requires consistent attention and care. Here are some key factors to consider:

• Temperature: Onions prefer temperatures between 65-75°F (18-24°C). Avoid extreme temperature fluctuations.
• Light: Ensure your onions receive adequate light. If growing indoors, supplement natural light with artificial grow lights. A combination of red and blue light spectrums are ideal.
• Nutrient Solution: Regularly monitor and maintain the nutrient solution. Change it every 1-2 weeks (DWC) or 2-3 weeks (Kratky) to prevent nutrient imbalances and the build-up of salts. Be sure to always refill with nutrient-rich solution, not plain water, when topping off water levels.
• pH Levels: Regularly test and adjust the pH of the nutrient solution. Onions thrive in a slightly acidic environment, with an ideal pH range between 6.0 and 6.5.
• Air Circulation: Ensure good air circulation around your onions. A small fan can help prevent fungal diseases, particularly in humid environments.
• Pruning: Trim any yellowing or dead leaves to encourage new growth.

Troubleshooting Common Problems

Like any gardening method, hydroponic onion growing can present some challenges. Here are some common issues and how to address them:

• Nutrient Deficiencies: If your onions exhibit signs of nutrient deficiencies (yellowing leaves, stunted growth), check the pH of your nutrient solution and make sure you’re using the correct dilution rates of nutrients. Replace the solution if needed.
• Algae Growth: Algae can grow in the nutrient solution if exposed to too much light. To prevent this, use an opaque container or wrap the container with a dark material. Regularly changing the solution also helps. You may also add an algaecide if needed.
• Root Rot: If the roots appear brown or slimy, it could be a sign of root rot. Ensure the nutrient solution is adequately aerated. Use a hydrogen peroxide solution (3%) to treat the root rot; use 1 tsp per gallon of nutrient solution. Allow the hydrogen peroxide solution to sit in the hydroponics system for 24 hours, then change the nutrient solution completely.
• Pests: Though less common in hydroponics, pests such as aphids or spider mites can occasionally appear. Treat the affected plants with insecticidal soap or neem oil.
• Bolting: If your onions begin to bolt, that is send up a flower stalk, this may mean that the temperature is too high for growing bulb onions, or the onions have reached maturity. You can cut the flowers off and use them, or harvest the onions. For bulb onions, try to maintain temps between 65-75F, and try not to let them get too hot.

Harvesting Your Hydroponic Onions

The time it takes for your hydroponic onions to mature will depend on the variety and your growing conditions. Generally, you can expect to harvest green onions in about 2-3 weeks. For bulb onions, it will take much longer, usually around 3-4 months.

Harvesting Green Onions

You can harvest green onions (also known as scallions) as needed, by simply cutting off the green stems at the base of the plant. New green shoots will grow from the bulb, allowing for multiple harvests. Be sure to harvest only the green parts and allow the onion to grow more leaves, and bulbs if desired.

Harvesting Bulb Onions

Bulb onions are ready to harvest when their tops begin to fall over and turn yellow. Once the bulbs begin to mature, you will start to see the bulb start to protrude out of the soil. Once the tops start to droop over and become discolored, carefully lift the entire plant, bulb and all, from the net pot. Allow the bulbs to dry for a day or two before storing them. The curing process allows the onions to develop a papery skin which will help with long term storage. You will need to hang dry your onions, and be careful to not allow them to get wet, as this may cause spoilage. A dark room that is cool and dry is a good place for drying and storing onions.

Conclusion

Growing onions in water is a fun and rewarding way to experience hydroponics. With a little patience and attention, you can enjoy a consistent supply of fresh onions year-round, regardless of your space or weather conditions. Whether you’re a beginner or an experienced gardener, the world of hydroponic onions is worth exploring. So, gather your supplies and get ready to grow some amazing hydroponic onions!