5 Tips For Growing Great-Tasting Hydroponic Spinach

Hydroponic gardening is the ideal growing system for enthusiastic gardeners who don’t have an outdoor garden space. It is also ideal for growing spinach, as you can perfectly control the growing environment to produce an abundant yield with this finicky plant. Let’s look at how to grow spinach hydroponically.

To grow delicious hydroponic spinach, start by cold stratifying your seeds. Soak a seed plug in water and then sow 4 to 5 seeds in each plug. Keep them well watered and pinch out all but the strongest seed that spouts in each plug. Start new seeds every few weeks for a continuous, year-round harvest. Move the seedlings into your hydroponic system when the roots emerge from the seed plug and start the spinach on a 1/4 diluted solution before gradually increasing the solution strength. Keep the temperature of your spinach plants between 4°C to 24°C (40-75°F), and limit their light to at most 12 to 14 hours a day.

Growing spinach in a hydroponic system is ideal for summer growing, since the long hot days of summer will cause spinach to bolt. Because of these specific growing requirements, many people find spinach difficult to grow without soil and end up with strong, bitter leaves. But follow these steps below and you will have great tasting spinach all year long from your hydroponic garden.

Growing Spinach In A Hydroponic Garden

To grow spinach in a hydroponic system, the seeds are started in seed plugs. These plugs are then transferred to a Nutrient Film Technique (NFT) or Deep Water Culture (DWC), where they are fed a nutrient solution to grow until harvest. A spinach plant has fairly shallow roots, so your hydroponic system does not need to be very deep. Regardless a DWC system is probably the easiest way to get started growing hydroponically, and you can make your own very cheaply.

There are many advantages to gardening hydroponically. Particularly, you don’t have to worry about soil-borne pests, and many other bugs and diseases are completely eliminated. Also, you have absolute control over the growing conditions of your crop. This is particularly necessary with spinach. Many people who grow spinach hydroponically end up with bitter tasting leaves, which is a pretty disappointing turnout after so many weeks of dedicated cultivation.

The main cause for an unsavoury spinach harvest is because spinach is a light-feeding cool-season vegetable. With too much light and excessive heat, spinach will quickly bolt and go bitter, even in the garden. Here are 5 tips for how to grow the best tasting spinach in the hydroponic garden.

  1. Start the seeds off right
  2. Continuous planting for a continuous harvest
  3. Take care when you transplant
  4. Monitor solution strength
  5. Control light and heat

1. Start The Seeds Off Right

Spinach seeds by Carmen Edenhofer
Image by Carmen Edenhofer

To end with the best produce, you need to start with the best seeds. Use the freshest spinach seeds possible to grow in your hydroponic garden. Spinach seeds generally remain viable for 2 to 3 years, but the newer the better. When growing in a hydroponic system, it is generally a good idea to cold stratify your spinach seeds by keeping them in the fridge for 1 to 3 weeks before sowing them as this will generally produce healthier spinach plants.

Choose your starter plug to grow your spinach, such as this one here, and soak the plug in water for 24 hours or overnight. Many people experience low to no germination while growing spinach hydroponically, so sow 4 to 5 seeds into each plug. Keep them warm and moist while they are germinating. The seeds will germinate and grow best when they are between 7C and 20C (44°F-68°F) and are watered or misted every day to maintain an even moisture.

Just add water

While your seeds are germinating, only use water to help them grow. Even when they are young seedlings, they do not need nutrient solution until they have been transplanted into your hydroponic system.

Once the seeds have germinated, it is time to choose the best plant in each plug and pinch out the rest. This will give you the strongest spinach plant which will grow into the healthiest, best tasting spinach. It is important to always pinch off the undesirable shoots, and never pull them out. Pulling them runs the risk of tearing the roots of the plant you want to keep, or pulling it out altogether.

2. Continuous Planting For A Continuous Harvest

When you are harvesting your spinach, you can trim off a few leaves at a time (or cut the plant right down) and it will regrow more leaves. However, this cannot go on indefinitely. Eventually the quantity and quality of the leaves will diminish and the plant will have reached its end. To avoid running out of fresh spinach, plant a successive crop every 2 to 3 weeks rather than all your plants in one go. Then you will have a continuous harvest of fresh, good-tasting leaves available all year.

3. Take Care When You Add Solution add solution only when your plants are big enough

You can either start the seeds directly in your hydroponic system or transplant them in later. In either case, it is important to wait until the plants are big enough before starting them on a nutrient solution. If you start the spinach on a solution too early, they are more likely to grow bitter leaves. It is best to wait until your spinach’s roots have started growing out of the plug. At this point, the plant is usually around 5cm to 8cm (2-3inches) tall with 3 or 4 leaves, and it is ready to start receiving the nutrient solution (see below on how to introduce solution).

Some growers like starting their seed plugs directly in a hydroponic system. If you do this, make sure your root plug does not sit directly in the water or it will get too wet and will rot. Here is a video that shows how to do this in a very simple way that you can easily make at home for cheap.

Alternatively, you can start your seed plugs in trays, and then transplant them into your hydroponic system. Your seedlings are ready to be transplanted when they are big enough to be started on the nutrient solution. Transplant your seedlings by placing the plant and the entire plug into your hydroponic growing system. Spinach plants can generally be spaced about 10cm to 12cm (4-5inches) apart. They can be placed closer if you are harvesting baby greens, but give them more space if you plan on letting them mature longer.

4. Monitor Solution Strength

Once your seedlings are big enough, they can be started on a solution. Most seedlings require a diluted solution, but spinach shoots require an extra weak dilution. When you first start spinach on a hydroponic nutrient solution, the solution should generally be diluted to approximately 1/4 strength. From this weak starting point, you can slowly increase the concentration until it is full strength, or as recommended by the manufacturer.

Just like soil fertilizers, hydroponic nutrient solutions are rated by the N-P-K ratio, which stands for the quantity of nitrogen, phosphorus, and potassium in the solution. While a well balanced solution is generally best, spinach thrives with a slightly higher quantity of nitrogen and phosphorus. Remember to never over-feed your spinach as this is a leading cause of bitter leaves. It is an especially good idea to decrease the concentration of your nutrient solution again as your plants near harvest.

Spinach prefers a pH level of 5.5 to 6.5. While most solutions are generally fairly balanced in terms of acidity, it is still a good idea to periodically check the pH of your system to make sure it remains fairly neutral.

5. Control Light And Heat

As we said before, spinach is a cool-season plant. Whether you are growing hydroponically or in the garden, light and heat are some of the key components to growing great spinach: too much of either is bad for spinach.

When spinach will bolt if it is exposed to excessive light or heat. Bolting is when a plant is growing outside of its ideal conditions and puts all its energy into producing seeds as a means of self-preservation. When spinach bolts, it will create a thick stalk with seed heads and bitter tough leaves.

Need a drink?

When growing spinach in soil, too little water will also cause spinach to bolt. Thankfully, you don’t have to worry about lack of water in a hydroponic garden.

To keep your spinach from bolting and the leaves from turning bitter, it is important to control how much light the plants get. Limit the light to make sure your spinach gets at most 12 to 14 hours of light per day. More light than that will make your spinach think summer is here, and the cool-season plant will go to seed.

LED light bulb by Carmen Edenhofer
Image by Carmen Edenhofer

That being said, you need to provide sufficient, good quality, light preferably in the blue colour spectrum. Fluorescent lighting is a very popular choice for hydroponic growing due to its low start-up investment. LED grow lights are a more environmentally friendly option. For a small, cost-effective setup, you can even use a lamp fitted with an LED daylight bulb on a timer.

To grow tender and flavourful spinach leaves, it is also imperative to control the temperature. Spinach’s ideal temperature is between 4°C to 24°C (40-75°F). Over 24°C, spinach will start to bolt so it is important to keep it cool.

If you are growing your spinach over the summer, it might be hard to keep the temperature of your house down. In this case, position your hydroponic garden in the coolest spot of your house and out of direct sunlight.

Spinach is a great vegetable for hydroponic growing. Though it can be a bit tricky, follow these steps and you will have great tasting, home-grown spinach in 30 to 45 days. Then all you need is a little olive oil.