Radish hydroponics: radish growing in the planting spot of a HydroFlex Tower

Growing vegetables without soil

Growing radishes in a hydro tower: fast, crunchy and with leaves

Radishes are ready to harvest in a few weeks and grow really well in the tower. Here I show you how I germinate them, why only one seed belongs in the basket and why you should never throw away the leaves.

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pH 5.5 to 6.5

target range for the nutrient solution

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EC 0.4 to 1.6

like lettuce

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15 to 20 °C

for germination, radishes are dark germinators

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250 to 350 PPFD

indoors, not longer than 14 hrs

Why I still grow radishes in the tower

I admit: a bunch of radishes doesn’t cost much at the discount supermarket. Still, radishes work really well in the hydro tower, and they’re ready to harvest faster than almost anything else. They’re perfect for beginners, because after a few weeks you see whether your system is running.

And you never know what’s coming. The future is written in the stars. If you know how to grow your own vegetables, you’re prepared. So: start your first experiments, radishes are ideal for that.

Radish in the net pot of a hydro tower at the window — The bulb grows at the top in the net pot, the roots hang in the nutrient solution.

My experiment: two radishes in one basket

I wanted more yield and put two radishes into one planting basket. That definitely didn’t go well: the two got in each other’s way, neither bulb became properly round. Since then my rule is: one seed, one basket, one bulb.

Anzuchtkarte · frankiesgarten.deRadieschenVom Samen bis zur Knolle in wenigen Wochen

Meine Notizen

Sorte:	Hersteller:

KeimtypDunkelkeimer

Keimen bei15 bis 20 °C

Keimdaueretwa 3 bis 5 Tage

Samen je Würfel1

pH-Ziel5,5 bis 6,5

Wasser18 bis 22 °C

Lichthöchstens 14 Std.

Pumpe drinnen5 an / 30 aus

Dünger, EC und pH

Phase	EC (mS/cm)	Frankies Dünger	pH
Anzucht (erste Blätter)	0,4	0,5 ml pro Liter	5,5 bis 6,5
Jungpflanze	0,8	1 ml pro Liter	5,5 bis 6,5
Wachstum im Tower	1,2	2 ml pro Liter	5,5 bis 6,5
Knolle bis Ernte	bis 1,6	bis 3 ml pro Liter	5,5 bis 6,5

Zeitplan und Beobachtungen

Ausgesät am:

Gekeimt nach:Tagen

Erste echte Blätter nach:Tagen

In den Tower nach:Tagen

Knolle sichtbar nach:Tagen

Geerntet nach:Tagen

Blätter gegessen:mal

Pflege

Nur ein Samen pro Würfel, zwei behindern sich.
Samen in den Schlitz legen, Deckel drauf: Dunkelkeimer.
Kühl halten, über 22 °C schießen sie gern.
Licht höchstens 14 Stunden, sonst schießen sie.
Ernten, solange die Knolle knackig ist.
Blätter nie wegwerfen: als Salat essen.

⚠️ Darauf achten: mögliche Schädlinge

Erdflöhe: viele kleine Löcher in den Blättern, die Käfer springen weg. Draußen Netz.

Kohlfliege: nur draußen: Maden fressen Gänge in die Knolle. Netz drüber.

Blattläuse: an Blattunterseiten. Mit Wasser abbrausen.

Falscher Mehltau: gelbe Flecken oben, grauer Belag unten. Luft und Abstand.

Mein Tipp für draußen: Ein feines Insektenschutznetz über den Tower, dann haben Erdflöhe und Kohlfliege keine Chance.

Wasserwechsel und Messwerte

Datum	Wasser neu	EC	pH
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Datum	Wasser neu	EC	pH
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frankiesgarten.de/anleitungen/gemueseanbau/radieschen-hydroponik/Fragen? WhatsApp 0176 436 444 63

Stage	EC (mS/cm)	Frankie’s nutrient	pH
Seedling (first leaves)	0.4	0.5 ml per litre	5.5 to 6.5
Young plant	0.8	1 ml per litre	5.5 to 6.5
Growth in the tower	1.2	2 ml per litre	5.5 to 6.5
Bulb until harvest	up to 1.6	up to 3 ml per litre	5.5 to 6.5

Radish profile

What	Value
Plant group	brassica, bulb with edible leaves
Germination type	dark germinator, cover seeds lightly
Germination temperature	15 to 20 °C
Germination time	about 3 to 5 days
Seeds per cube	1
pH value	5.5 to 6.5
EC value	0.4 (seedlings) to 1.6 (bulb)
Light indoors	250 to 350 PPFD, at most 14 hours
Water temperature	18 to 22 °C
Harvest	about 4 to 6 weeks after sowing
Special point	leaves are edible and healthier than the bulb

The seed packet counts

There are spring varieties and varieties that don’t bolt so quickly even with long days. For indoors under the lamp and for summer, choose a bolt-resistant variety. Always check your packet.

You’ll find all values to print on the growing card above. The values for all other plants are in the pH and EC table (German).

My tip for your radishes

Small, fast, for the window: the HydroFlex Tower Classic 3+

8 litre tank and room for 9 plants and more. Just right for radishes, lettuce and herbs on the windowsill.

Black Friday already on, only until 30 Nov: From an order value of €200 you get free: a seedling station for 13 plants, 150 ml Frankie’s liquid nutrient, 25 seedling cubes and 13 lettuce seeds.

To the Classic 3+Which tower suits me?

Your growing plan

Here you can see all phases at a glance. Tap a phase, below I explain each step in detail.

1Germination 2Seedlings 3Tower 4Bulb 5Harvest

Step 1 · in the seedling box

Let radishes germinate cool and dark

Germination temperature15 to 20 °C

Germination typeDark germinator

Germination timeabout 3 to 5 days

Nutrientnone yet

Only one seed per cube.
Put the seed in the slit.
Lid on the seedling box.
As soon as it germinates: lid off, lamp on.

Not too warm: Above 22 °C radishes quickly get long and thin.

What you need now: seedling box with lid or the seedling mat with 100 cubes.

Read in detail ›

1Germinating in the seedling box

about 3 to 5 days · cool and dark

I start radishes in foam cubes. Exactly one seed goes into each cube. Radishes are dark germinators: put the seed in the slit, with the lid on the seedling box it lies in the dark. At 15 to 20 °C they germinate fast, often after just 3 days.

Temperature

15 to 20 °C

Germination type

Dark germinator

Duration

about 3 to 5 days

Nutrient

none yet

As soon as it germinates: lid off, lamp on

Radishes stretch very quickly. If the lid stays on too long or it’s too warm, the seedlings get long and thin. Then no nice bulb forms later.

What I use for this: the seedling box with lid from my shop.

2Briefly into the seedling station

about 1 to 2 weeks

Once the seed leaves are open, the cube goes into the net pot of the seedling station. I start with 0.5 ml of Frankie’s nutrient per litre, which gives an EC of about 0.4 with soft water. With the first true leaf it goes to 1 ml per litre.

0.4 to 0.8

5.5 to 6.5

Water

18 to 22 °C

Light

at most 14 hrs

Not too much light

Radishes are long-day plants. When days get long and warm, they’d rather form flowers than bulbs, they bolt. That’s why I leave the lamp on for at most 14 hours with radishes. That’s also why radishes are harder outdoors in high summer than in spring and autumn.

My recommendation

Measure pH and EC reliably

Without a meter you’re just guessing. A combination meter shows you pH, EC and temperature at a glance.

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3Into the tower

with the first true leaf

Radishes form the bulb early, so they go into the tower soon. I put the net pot with the cube into the planting spot. The bulb then grows at the top in the net pot, just like in my photo, the roots hang freely in the nutrient solution.

One basket, one radish

My attempt with two radishes in one planting basket went wrong. They took each other’s space, neither bulb became properly round. You get more yield by sowing more often: a few new cubes every one to two weeks, then you harvest continuously.

Pump timing

Indoors my pump runs for 5 minutes, then pauses for 30 minutes. Outdoors in blazing sun I switch to 15 minutes on and 15 minutes off.

Angebot

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Digital timer with cycle function. I set 5 minutes on and 30 minutes off.

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From my shop

Everything for your soil-free start

HydroFlex Tower for indoors and outdoors, seedling box, seedling station, support rings and my own nutrient. After you buy, I’ll help you on WhatsApp.

To the shop ›

4The bulb gets round

until harvest · cool and even

Now I increase to 2 ml nutrient per litre, later up to 3 ml, then the EC is 1.2 to 1.6. Radishes like it cool, ideally between 15 and 20 °C. In heat they get hot, pithy or bolt.

1.2 to 1.6

5.5 to 6.5

Water

18 to 22 °C

Light

at most 14 hrs

Even means crunchy

A radish bulb splits if it first stands dry and then suddenly gets lots of water. In the tower that hardly happens as long as the tank never runs empty.

Your water	EC without nutrient	What you do
soft	below 0.3	feed normally, measure the pH more often at first
medium	0.3 to 0.5	feed by EC, a little less room is left for nutrient
hard	above 0.5	mix half and half with rain or RO water

5Harvest: bulb and leaves

about 4 to 6 weeks after sowing

Harvest your radishes as soon as the bulb is about 2 to 3 cm and nice and round. If you leave them too long, they get pithy, hollow and very hot. I pull out the whole plant with the net pot, dispose of cube and roots and put in a new cube.

Freshly harvested radishes from the hydro tower — Freshly harvested from my tower.

Never throw away radish leaves

This is really important to me: don’t throw the leaves away. You can eat radish leaves like lettuce, raw, in a mixed salad, in pesto or briefly steamed like spinach. They taste slightly nutty and a little hot.

Aha: the leaves are healthier than the bulb

A study compared leaves and bulbs of red radishes. The leaves contained about twice as much vitamin C and twice as many polyphenols, around four times as many flavonoids, and the antioxidant capacity was a good three times higher than in the bulb. On top of that there are mustard oils, which provide the heat and are being studied more closely in research. If you throw away the leaves, you throw away the most valuable part.

Source: Goyeneche et al., Journal of Functional Foods, 2015: chemical composition and antioxidant capacity of leaves and roots of red radishes. The same applies to kohlrabi leaves: I make crispy chips from them.

Light and location

Indoors radishes need a lamp with 250 to 350 PPFD at leaf height. The duration is important: at most 14 hours a day. More light per day makes radishes bolt.

If light is missing, the stems get long and the bulb stays thin. Hang the lamp at the side of the tower, so all levels get light.

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60 cm LED grow light, good for the side of the tower.

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Outdoors

Outdoors spring and autumn are the best time for radishes. In high summer with heat and long days they bolt easily. Then bolt-resistant varieties and a semi-shady spot help.

Pests on radishes: what I look out for

Radishes are brassicas like cabbage. Indoors you hardly have problems, outdoors you should protect them.

🪲

Flea beetles

Tiny beetles, lots of small round holes in the leaves. They jump away when you tap the leaf. Worst in heat and drought.

🪰

Cabbage root fly

Only outdoors: the maggots eat tunnels into the bulb. A fine net keeps the fly away.

🐜

Aphids

Sit on the leaf undersides. Rinse off with water, outdoors hoverflies help.

🍂

Downy mildew

Yellow spots on top, grey coating underneath. Ensure air movement, remove affected leaves.

My tip for outdoors

A fine-mesh net over the tower protects against flea beetles and cabbage root fly. Flea beetles crawl through any gap though, so outdoors I prefer to sow radishes in spring and autumn.

View insect net*

* I earn a commission if you buy, your price stays the same.

Common problems and what helps

No bulb, only leaves

Usually too warm, too little light or days too long. Keep the temperature below 20 °C, give enough light, but at most 14 hours.

Radishes bolting

Long days and heat make radishes flower. Limit the lamp to 14 hours and choose a bolt-resistant variety.

Pithy and hollow

The bulb stood too long. Harvest as soon as it’s 2 to 3 cm.

The bulb splits

Alternating dryness and lots of water. Never let the tank run empty.

Very hot

Heat and lack of water make radishes hotter. Kept cool and evenly supplied, they stay milder.

Two radishes in a basket stay small

They get in each other’s way. Always just one seed per cube and planting spot.

Fancy more radishes? You’ll find the HydroFlex Tower Classic 3+ for the windowsill in my shop ›

FAQ about radishes in hydroponics

Can you grow radishes in a hydro tower?

Yes, they grow really well in the tower and are ready to harvest after about 4 to 6 weeks.

Do radishes need light or darkness to germinate?

Radishes are dark germinators. Put the seed in the slit and the lid on the seedling box.

At what temperature do radishes germinate?

At 15 to 20 °C.

How long does germination take?

About 3 to 5 days.

How many seeds go into one cube?

Exactly one. Two radishes in one basket get in each other’s way, I tried it.

What pH value do radishes need?

Between 5.5 and 6.5.

What EC value do radishes need?

For seedlings 0.4, as a young plant 0.8, in growth 1.2 and up to 1.6 until harvest.

How much nutrient do radishes need?

With Frankie’s nutrient and soft water: 0.5 ml per litre for seedlings, then 1 ml, in the tower 2 ml and up to 3 ml per litre.

How long does it take until harvest?

About 4 to 6 weeks after sowing.

When are radishes ready to harvest?

When the bulb is about 2 to 3 cm and nice and round.

Why are my radishes getting pithy?

They stood too long. Harvest in time.

Why aren’t my radishes forming a bulb?

Usually too warm, too little light or too much light per day. Below 20 °C and at most 14 hours of light.

How much light do radishes need indoors?

250 to 350 PPFD at leaf height, at most 14 hours a day.

Can you eat radish leaves?

Yes, absolutely. Raw as salad, in pesto or briefly steamed like spinach. Never throw them away.

Are radish leaves healthy?

A study found about twice as much vitamin C in the leaves as in the bulb, twice as many polyphenols, around four times as many flavonoids and a good three times higher antioxidant capacity.

How do I get more yield?

Not several seeds in one basket, but sow again every one to two weeks. That way you harvest continuously.

Which pump times do I use?

Indoors 5 minutes on and 30 minutes off, outdoors in heat 15 on and 15 off.

How do I protect radishes outdoors?

With a fine-mesh net against flea beetles and cabbage root fly.

You’ll find more vegetables without soil under vegetable growing in the hydro tower. You’ll find the right HydroFlex Tower for your space in my shop.

Continue with your own growing

My book

Step by step into hydroponics

168 pages, simply explained for beginners and with videos on the topics (in German). Exactly how I grow myself: from sowing to harvest.

More about the book ›

Free

Which tower suits you?

A few questions about space, location and what you want to harvest, and you get a recommendation.

To the tower advisor ›

Questions about your setup? Message me on WhatsApp.

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