⏳ 16 min read · Last updated: September 2026
You can grow arugula, kale and spinach together in one reservoir, and they make a better team than most mixed plantings. All three are cool-season greens, all three like the same pH, and their feeding ranges overlap. Put them in one tote and you get a peppery leaf, a sturdy leaf and a soft one from a single tank, picked a few leaves at a time for weeks.
There is one catch, and it decides the whole recipe. Spinach is the fussy member of the group: it wants shorter days and colder water than the other two. So the tank runs on spinach’s terms, and the other two are happy to go along with it. Here is the exact recipe: container, spacing, feed, light, temperature and a harvest rhythm. If you are brand new to hydroponics, the apartment hydroponics beginner’s guide covers the basics first.
How to Grow Arugula, Kale and Spinach Together: The Recipe
- Six plants, two of each, in an aerated tote of 10 gallons or more, or one of each in about 5 gallons.
- Run the light for 12 hours a day, because spinach bolts on longer days. Arugula and kale grow a little slower at 12 but do fine.
- Keep the water at 65 to 68°F (18 to 20°C), where spinach’s cool range meets the other two, and the room under 70°F (21°C).
- Start the shared solution at EC 1.5 and pH near 6.0. Once plants are established, 1.6 to 1.8 is where all three ranges overlap.
- Expect first cuts in about 30 to 45 days from seed, then pick outer leaves every few days.
The Three Crops Side by Side
Each crop’s own numbers come from the crop table on this site. The last column is the setting the shared tank uses.
Why These Three Share a Tank So Well
Most mixed plantings are compromises that leave one crop unhappy. This one is closer to a natural fit. Arugula, kale and spinach are all cool-season leafy greens, so they want a cool room and dislike heat. All three sit in the general pH range of 5.5 to 6.5. And their feeding ranges overlap between EC 1.6 and 1.8, which is unusual for three different crops.
They also fill different parts of the tank. Arugula grows quickly and stays compact at 6 to 10 inches. Spinach forms a low rosette of about 8 to 12 inches. Kale is the big one, reaching 12 to 18 inches unless you keep picking it. So in practice the tank has a tall back row and a low front row, and each plant gets its share of light.
The Catch: Spinach Sets the Rules
Spinach bolts more easily than the other two. It is a long-day plant: once the day passes about 13 to 15 hours, it tends to send up a flower stalk, and the leaves turn bitter. It also wants colder water, 59 to 68°F (15 to 20°C), because warm water feeds the fungus that rots its roots. Arugula and kale tolerate both of those conditions well, while spinach cannot tolerate theirs. So the tank runs a 12-hour light and cool water, and that single decision makes the trio work. If you want to grow spinach on its own, the spinach guide goes deeper into it.
The Container and Layout
Leafy greens drink more than their size suggests, and three kinds of roots in one small tub turn the water over fast. Per plant, a DWC setup wants 1 to 2 gallons for arugula and spinach, and 2 to 3 gallons for a full kale plant. So size the tank to match:
- The six-plant recipe: two kale, two spinach, two arugula, in an opaque tote holding 10 gallons or more.
- The small version: one of each in a tote of about 5 gallons.
- For either size, use 2-inch net cups for arugula and spinach, and 2 to 3 inch cups for kale.
- Run an air pump with an air stone in the middle of the floor, and fit a check valve in the line.
Aerated water (DWC) suits this mix best, because kale grows into a large plant that would drink a passive tank dry. If you only want baby leaves, a Kratky tote planted all at once works too, since all three can be grown that way when cut young; the Kratky tote setup shows how. The pump hums, so put it on a folded towel and see the quiet air pump roundup for the quietest ones. DWC vs Kratky explains the two systems if they are new to you.
Laying Out the Lid
Put the kale in the back row, 8 to 10 inches apart, where its height will not shade anything. Arugula and spinach go in the front row, 4 to 6 inches apart. Stagger the rows so no plant sits directly behind another. Cover any hole you are not using, because light in the water grows algae. When a tote lid starts to sag under wet plants, stand an upturned pot on the floor of the tote under the middle to hold it up.
Starting the Seedlings
Start all six in rockwool cubes soaked at pH 5.5, under a dome, and feed them at EC 1.0 to 1.2 once they sprout. Kale comes up in 4 to 7 days, arugula in 5 to 7, and spinach is the slowest at 5 to 10. So sow spinach a few days before the others if you want them to go into the tank together. Starting seeds in rockwool covers the method, and when to transplant seedlings tells you when roots are ready.
The Feed: EC, pH and the Routine
Start the shared tank at EC 1.5. It is the middle ground I use for any mixed reservoir, and it is kind to young plants. Once the plants are growing well, you can raise it to 1.6 to 1.8. That band sits inside all three crops’ ranges: the top of arugula’s and spinach’s, and the bottom of kale’s. Going higher mostly helps the kale while risking tip burn on the others, so stop at 1.8. Spinach and arugula both burn above about 2.0.
Hold the pH near 6.0. Spinach prefers the lower end of the range and starts to struggle above about 6.2, so if its leaves pale while the others look fine, bring the whole tank down toward 5.8. Kale is the one to watch for magnesium: yellowing between the veins of older leaves usually means the pH has drifted high. The pH and nutrient calculator works out doses for your tote, and EC for herbs and greens explains what the numbers mean.
- Fill the tote with cool water, add part A and stir, then add part B and stir again. Never mix the two concentrates together undiluted.
- Bring the EC to 1.5 with a little more concentrate or plain water.
- Adjust the pH last, toward 6.0. When you use pH Down, dilute it in a cup of tank water first and pour that back in.
If your water is soft or filtered, a low dose of Cal-Mag helps. Spinach goes pale without enough magnesium, and kale shows calcium and magnesium trouble quickly. Do you need Cal-Mag helps you decide, and mixing two-part nutrients shows the method.
The Daily and Two-Week Routine
Every day, top the tank back up with plain water adjusted to pH 6.0, never with nutrients, since the plants drink water faster than they use the salts. The top-off guide explains why. Check the EC and pH a couple of times a week with a reliable EC meter. Every 2 weeks, lift the lid with the plants onto a tray, empty and rinse the tote, and refill it with fresh solution. If the pH keeps wandering, why pH keeps drifting explains the usual causes.
Light: Why the Tank Runs 12 Hours
One light runs one schedule, so the whole tank gets spinach’s 12 hours on and 12 off. Longer days push spinach toward bolting, and 14 hours sits inside its risk band. Arugula and kale normally run 14 hours on this site, but they grow well at 12, just a little slower. Arugula actually benefits, because long days are one of the things that make it bolt too.
A shorter day needs brighter light to deliver the same daily total. Aim for about 300 to 400 PPFD at the leaves, which over 12 hours works out to a DLI of about 13 to 17, the band spinach wants and plenty for the other two. Hang the panel 6 to 8 inches above the tallest leaves, which will usually be the kale, and raise it as they grow. Those inches are a starting point for a typical home LED: pale, stretching plants mean lower, bleached leaves mean higher. The grow light calculator checks whether your fixture covers the whole tote, and grow light distance goes through the adjustment. A timer from the compact timers roundup keeps the 12 hours exact.
Temperature: The Cool Room Rule
This trio belongs in a cool room. Hold the air at 60 to 70°F (15 to 21°C) and the water at 65 to 68°F (18 to 20°C). That water band is narrow, because it is where spinach’s cool range (59 to 68°F) meets the lower edge of the others’ (65 to 75°F). Above 68°F, spinach’s risk of root rot and bolting climbs quickly. Above about 72°F in the room, arugula starts to bolt as well.
A cool bedroom, a north-facing room or a spot away from the kitchen works. Keep the tote off the fridge, away from radiators and out of afternoon sun, and remember the grow light adds heat of its own; grow light heat in apartments covers that. Never drop ice into the reservoir. The sudden cold shocks the roots and wears off within the hour. Instead, stand a frozen bottle against the outside of the tote, or move it somewhere cooler. More fixes for a warm flat are in small system temperature problems.
If your apartment simply runs warm, be honest with yourself and drop the spinach. Arugula and kale share a tank happily on the usual 14 hours at 65 to 75°F water. Grow spinach in winter, or in a separate jar in the coolest spot you have.
Harvesting and Replanting
All three are cut-and-come-again greens. Pick the outer leaves, leave the center to keep growing, and the tank keeps giving for weeks.
- Arugula is first, at 30 to 40 days from seed. Take outer leaves an inch above the crown every 3 to 5 days.
- Spinach follows at 35 to 45 days, with baby leaves from about 25. Snip outer leaves at the base every 3 to 7 days, and leave at least 4 young leaves in the center.
- Kale gives baby leaves at 30 to 45 days and full leaves at about 8 weeks. Take a few outer leaves per plant every 5 to 7 days.
Replanting the Front Row
Arugula and spinach each give about 4 to 6 weeks of cutting before they bolt or lose quality, while kale keeps going for 6 to 10 weeks or more. So you replace the front row roughly twice for every kale plant. When a plant stretches upward and turns bitter, pull it and put in a seedling you started a few weeks earlier. The seed to harvest calculator tells you when to sow those replacements, and the kale guide covers picking kale so one plant lasts. The arugula guide does the same for arugula.
Each crop’s pH, EC, light, temperature, spacing and harvest figures are the ones the crop table on this site uses, and the crop sources page lists the research behind them for arugula, kale and spinach. The cool water and the 12-hour day for spinach follow the Cornell CEA handbook and published photoperiod trials, and Oklahoma State’s EC and pH guide gives crop feed ranges. The starting EC of 1.5 for a mixed tank and the light height in inches are my own practice, not research figures.
Troubleshooting a Mixed Greens Tank
When one crop struggles and the others look fine, the tank is usually tilted toward the other two. When all three struggle, check pH and temperature first.
| What you see | Most likely cause | What to do |
|---|---|---|
| Spinach shoots up a flower stalk | Warm room, or the light is on too long | Keep the air at 60 to 70°F and also cap the light at 12 hours |
| Arugula bolting early | A hot room, especially above about 72°F | Move the tote somewhere cooler before you replace bolted plants |
| Pale or yellow spinach, while the others look fine | pH too high for spinach, or too little magnesium and iron | Bring the pH toward 5.8, and add low-dose Cal-Mag when the water is soft |
| Yellow between the veins on older kale leaves | Magnesium shortage, especially when pH drifts high | Lower the pH toward 5.8 to 6.0 and also check the feed has magnesium |
| Brown, crispy edges on arugula or spinach | EC pushed too high because of the kale | Dilute with plain water until it reads 1.5 to 1.8 |
| White powder on kale leaves | Powdery mildew, because the air is humid and still | Add a small fan and thin the leaves, so humidity stays at 70 percent or below |
| Brown, slimy roots, spinach wilting first | Water above 68 to 72°F, so oxygen runs short | Cool the tank and check the air stone before you treat the rot |
Root Rot Hits Spinach First
Spinach is the early warning in this tank. When its roots go brown and slimy while the others still look fine, the water is running too warm, and the other two are next. Cool the reservoir back to 65 to 68°F, make sure the air stone is bubbling, trim dead roots and change the solution. For an active infection, add 3 ml of 3% hydrogen peroxide per liter, as hydrogen peroxide for root rot explains, then run the tank at EC 1.2 to 1.5 for 4 to 7 days while it recovers. Preventing root rot covers stopping it coming back.
Mildew on Kale
Kale’s big leaves hold damp air, and in a humid room with no air movement they pick up powdery mildew. Keep the humidity at 50 to 70 percent, pick the oldest leaves regularly so air moves through, and run a clip-on fan on low. If white patches appear anyway, treating powdery mildew indoors covers the options.
A Word From Sarah
Buy a waterproof thermometer that stays in the tote, and read it at the warmest time of day, not in the morning. The whole recipe hangs on 65 to 68°F, and a reservoir that reads 66 at breakfast can sit at 72 by late afternoon under the lamp. Nobody sees that swing unless they look for it. Spinach does, though, and it tells you with a flower stalk a week later.
Frequently Asked Questions
Can arugula, kale and spinach grow in the same hydroponic reservoir?
Yes, and they share better than most mixes. All three are cool-season greens with the same pH range and overlapping feed ranges. The tank has to run on spinach’s terms: 12 hours of light, water at 65 to 68°F and a room under 70°F. Arugula and kale are happy with that.
What EC should I use for arugula, kale and spinach together?
Start at EC 1.5, the middle ground for a mixed tank. Once the plants are established, you can raise it to 1.6 to 1.8, which sits inside all three crops’ ranges. Stop there, because spinach and arugula get tip burn above about 2.0 even though kale would take more.
How many hours of light for a mixed arugula, kale and spinach tank?
Run 12 hours on and 12 off, because spinach bolts on longer days and one light can only run one schedule. Arugula and kale grow a little slower at 12 hours but do well. Aim for about 300 to 400 PPFD so the shorter day still delivers enough light.
What water temperature suits arugula, kale and spinach together?
Keep the water at 65 to 68°F (18 to 20°C), where spinach’s cool range meets the other two, and the room at 60 to 70°F. Above 68°F spinach risks root rot and bolting. Never cool the tank with ice; stand a frozen bottle against the outside instead.
What size container do I need for all three?
Allow 1 to 2 gallons per arugula or spinach plant and 2 to 3 gallons for a full kale plant. Two of each fit in an aerated tote of 10 gallons or more, and one of each fits in about 5 gallons. A small jar or a two-gallon tub is too little water for three root systems.
What if my apartment is too warm for spinach?
Drop the spinach and run arugula and kale together on the usual 14 hours with water at 65 to 75°F. They share a tank well at EC 1.5 to 1.8. Grow spinach in winter, or in a separate jar in the coolest spot you have.
When can I harvest arugula, kale and spinach?
Arugula is first, at 30 to 40 days from seed. Spinach follows at 35 to 45 days, and kale gives baby leaves at 30 to 45 days and full leaves at about 8 weeks. Pick outer leaves and leave the center growing, and all three keep producing for weeks.
Can I grow all three in a Kratky tote instead?
Yes, if you plant them all at once and pick them young. Arugula and spinach grow well in Kratky, and kale does too as baby leaves, but a full kale plant drinks a passive tank dry. For full-size kale and a tank you keep replanting, use an air stone.
How often should I change the water in a mixed greens tank?
Top off every day with plain water adjusted to pH 6.0, and change the whole reservoir every 2 weeks. Lift the lid with the plants onto a tray, empty and rinse the tote, and refill with fresh solution at EC 1.5 to 1.8.
Do hydroponic arugula, kale and spinach taste good?
Yes. Cool temperatures and a moderate feed give arugula a milder, peppery bite, spinach tends to be sweet and tender, and young hydroponic kale is softer than most shop kale. Strong feeds and warm rooms make all three harsher and more bitter.
Happy growing! 🌿
Sarah, Urban Hydro Space
Sarah Whitfield is the founder of Urban Hydro Space and an indoor gardening enthusiast dedicated to helping apartment dwellers grow fresh herbs and vegetables in small spaces. She researches hydroponic systems carefully from real specifications and verified buyer feedback, and shares practical tips and honest, clearly labeled product picks to make indoor gardening accessible for beginners.
