How to: Grow Spinach Hydroponically

By: Chris | Last Updated: November 17, 2020

While you may not gain instant strength like Popeye the sailor man, it’s hard to discount the healthy benefits of fresh leafy, green spinach. Spinach has long been credited with increasing vitality, restoring energy, and supporting healthy blood—and rightfully so.

This leafy green is pumped full of iron, vitamins K, A, C, and folate. You’ll also find it to be a good source of vitamin B2, magnesium, and manganese. 

With so many fine qualities—not to mention all that tastiness—it’s no wonder spinach is high on the list of those who have turned to hydroponic gardening so they can have a ready supply of fresh, high-quality veggies ready for harvesting.

Here’s what you need to know to grow spinach hydroponically.

Getting Started: Spinach Germination

Your first step to growing spinach hydroponically is to get the spinach seeds to germinate. 

Note: Before germinating, soak spinach seeds in water for 4-8 hours to accelerate the germination process.

Like all seeds, spinach germination takes place in three stages: soaking up moisture, developing new cells inside the seed, and finally, the visible emergence of the sprout.

Spinach seed germination happens best between 32 and 65°F. Spinach is a cool-weather crop so avoid heating pads when germinating spinach seeds.

For a hydroponic garden, it’s preferable to germinate the seeds without soil. One of the easiest methods is paper towel germination. It makes it easy to control moisture, it’s also easy to see when your seeds have germinated, and the damp paper towel keeps the seeds cool.  

Try to give your seeds about 12 hours of light daily. Fluorescent lighting works great for this. Blue light will enhance chlorophyll production and facilitate leafy growth, which is great for spinach.

Pre-soaked seeds should germinate and begin to sprout within 5 days. If you didn’t soak the seeds, you’d be waiting 10+ days for germination. When the spinach seedlings are about 2 inches tall, they’re ready to be transplanted into your hydroponic system.

As soon as the seed begins to sprout before it has time to develop much of a root system I place the seed in a starter plug soaked in .6 EC nutrient solution. My starter plugs of choice are called Rapid Rooter. They’re especially useful because they work for both hydroponic and soil-based planting.

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Hydroponic Spinach Fact Sheet

How to Germinate Spinach Seeds Hydroponically

To germinate spinach seeds hydroponically, you’ll need a grow medium the seeds can start in. Common seed starter plugs are rockwool, coconut coir, or products like Rapid Rooter from General Hydroponics.

If you’re using rockwool, make sure to pH balance the rockwool before planting seeds. To do this, soak the plugs in 5.5 pH water for 15-20 seconds.

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Rapid Rooter plugs will need to soak for a few hours before planting seeds. Okay, honestly I’ve never soaked them for more than a few minutes and have always had great results. If you wanna give ’em a 3-hour bath, go for it, but I don’t think it’s really necessary. These plugs are designed to hold a specific amount of water ideal for germination, so don’t water them unless they are drying out.

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Note: If you don’t have a humidity dome, you can use plastic wrap. If you use plastic wrap, place something in the seed tray that helps the plastic wrap “dome” around the tray, so it’s not in direct contact with seed starter plugs.

Bottom Watering with Rockwool
Bottom watering refers to adding water to the seed tray instead of directly on top of seed plugs. This method helps reduce mold growth and keeps the seed healthier.

To bottom water rockwool starter plugs, simply add water to the tray the plugs are in. Add only enough water to soak the bottom of the plugs. The plugs will wick water up to the seed.

Time to germinate: 6-10 days | Special requirements: 32-60°F | Difficulty: Medium

Growing Tips for Hydroponic Spinach

Spinach can be grown using various hydroponic systems, though a deep water culture system or nutrient film technique is usually preferred. I personally grow spinach using an ebb & flow system and have had great success.

Once you’ve transplanted your seedlings, avoid fertilizing them for a week. After that, treat your young spinach plants to ¼ strength hydroponic nutrients for two weeks. Young spinach plants thrive when calcium and magnesium levels are raised. However, spinach is nitrogen sensitive, so be careful nitrogen levels don’t get too high, or you could end up with leaf tip burn. Nitrogen is important, but you don’t want to overdo it!

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Once you’ve reached the two-week mark, you can move up to ¾ strength of hydroponic nutrients for one week, then go to full strength after that. 

Reality Check: Okay, if you’re growing spinach in a small system and want to work through reduced strength nutrient solutions that’s great. If you’re adding spinach into an already operating hydroponic system with mature plants, like lettuce, don’t worry about the nutrient strength too much. Spinach is pretty tolerant, and with lettuce growing at strength around 1.2 EC you shouldn’t have problems.

What is the optimal pH of Spinach?
Spinach is relatively forgiving in terms of pH, thriving in conditions with a pH level ranging from 6.0 to 7.0.

If you plan to grow spinach and lettuce in the same hydroponic container, a pH range of 6.0 to 6.5 will keep both plants happy and healthy.

You’ll also want to be sure you provide adequate oxygen level in the system. 

If you have problems with leaf yellowing, it could be because conditions are too cool, which can prevent the plant from taking up sufficient iron. The problem can also occur if the roots have been damaged during transplant or if you’ve overwatered the plants or allowed nutrient stagnation.

Time to Maturity: 45 Days | pH Range: 6.0-7.0 | EC: 1.8-2.3 | Light/Dark Cycle: 12hr/12hr | Hydroponic System: Any | Grow Medium: Any | Spacing: 6-8″

Photo of Fresh Organic Spinach

Harvesting Hydroponic Spinach

While it may take 45 days for a spinach plant to reach maturity, you can normally begin harvesting sooner. Once the plant has developed distinguishable inner and outer leaves, you can start harvesting the outer leaves. This harvesting method is no different from the “pick and come again” style of harvesting loose leaf varieties of lettuce.

I prefer to harvest spinach like this because it extends my plants’ growing cycle, which means I get to keep harvesting fresh spinach leaves for several weeks. I personally don’t store harvested leaves. Instead, I pick what I want to eat daily so that I can enjoy the wonderfully crisp texture and flavor of fresh off the plant spinach.

FAQ

Can spinach be grown hydroponically?

Yes, spinach thrives in a hydroponic garden. It’s a fast growing, lightweight plant that can be grown in virtually any hydroponic system.

How long does it take to grow spinach hydroponics?

40-45 days. The time to maturity will vary slightly depending on the variety. Most spinach varieties will reach maturity in 40-50 days.

Hydroponic gardening with optimal lighting will result is faster plant growth, increased yields, and earlier maturity. It’s common for hydroponic spinach to reach maturity as early as 35-40 days.

Can you grow spinach indoors year round?

Yes! Spinach can be grown indoors all year long. Indoor gardening allows you to control the environment, providing ideal growing conditions regardless of season.

Does spinach need direct sunlight?

Yes, spinach will be happiest in direct light. If you’re growing spinach indoors, it will grow best when directly under a grow light.

Placing spinach on the perimeter of the grow area will slow its growth.

Should you soak spinach seeds before planting?

Yes, soaking spinach seeds prior to germination will speed up the process a lot. Soaked seeds can germinate in as little as 5 days, compared to un-soaked seeds taking 10 or more days to germinate.

Can you harvest spinach after it bolts?

Yes, you can harvest spinach leaves after the plant begins to bolt, but they will be bitter. I continue to harvest leaves for a few days once a plant begins to bolt. After a week, the leaves will likely be too bitter to be enjoyable.

The bitter leaves of a bolting plant can add a nice flair to a salad mix when used sparingly.

Time to Grow Spinach Hydroponically

You’re ready to grow spinach hydroponically! Not only is it incredibly tasty, spinach also looks beautiful growing in your hydroponic garden. I keep spinach growing year-round and I think you are going to be amazed at how amazing it tastes when harvested fresh from a soilless garden.

Even the best organic produce from a grocery store won’t compare to what you’ll be able to grow at home!

Chris Cook started Happy Hydro Farm to share his passion for hydroponic gardening! Growing your own food is incredibly rewarding both physically and mentally. His mantra - "Take excellent care of your plants, and your plants will take excellent care of you."