I’m often asked if I get mold or algae in my indoor gardens.
I don’t – but that’s because I make sure to follow some simple rules!
In today’s post, I’ll explain why mold or algae can appear in a hydroponic garden and give you a few easy changes to make sure it stops happening.
the only thing I want to grow in my apartment are herbs and veggies – not mold!
Why Mold or Algae Appears in an Indoor Garden
Mold and algae both thrive in environments that are:
- Warm
- Humid
- Full of moisture
- Exposed to light
Basically.. everything that an indoor garden provides.
The same conditions that make a hydroponic system great for growing plants also make it easy for mold and algae to flourish.
And, once they appear, it’s easy for mold and algae to become entrenched.
The nutrient rich water, long hours of LED light and warm indoor environment can create a zen-like spa for mold and algae to form if you’re not careful.
How to Tell If You Have Mold or Algae
Mold:
- May spread to leaves or the top of plant cups
- Appears white, fuzzy, or powdery
- Often forms on the surface of the grow medium (like peat pods or sponges)
Algae:
- Has a musty smell when it builds up
- Slimy, green, or brownish
- Grows on the inside of the water reservoir, near light sources, or in tubing
How to Prevent Mold and Algae in Your Indoor Garden
1. Block Light from the Water Reservoir
Light hitting your water = algae party.
Use opaque covers or aluminum foil to wrap around plant pods and cover gaps.
If your system has a clear basin, paint or wrap it to prevent light from reaching the water.
2. Improve Air Circulation
Damp air encourages mold.
Use a small fan to keep air moving around your plants.
Don’t overcrowd your grow area—plants need space to “breathe.”
3. Control Humidity
Indoor environments can get humid—especially in small apartments.
Aim for 50-70% humidity
Open a window, use a dehumidifier, or run a floor fan if needed
4. Remove Dead Plant Material ASAP
Dead leaves = mold magnets.
Regularly trim off wilted leaves or stems
Clean up fallen plant debris from around the pods.
5. Clean Your Hydroponic System Between Cycles
Leftover residue and nutrients can feed mold and algae.
Make sure to rinse and scrub the basin, grow pods, and any tubing with soap and water. I also like to run a vinegar water cycle through the garden to sterilize all the nooks and crannies.
I made a tutorial for how to do that here, or you can watch this Youtube video.
And let everything dry fully before starting a new grow cycle.
How to Remove Mold and Algae If They’ve Already Appeared
If you’re already seeing growth, here’s how to get rid of it:
For Algae:
- Drain the water basin
- Scrub the inside with a vinegar or peroxide solution
- Replace with fresh water and nutrients
- Cover exposed areas to block light
For Mold:
- Gently scrape it off with a clean knife or spoon
- Rinse the grow pod under running water
- Use a diluted hydrogen peroxide spray (1 part peroxide to 3 parts water) and mist the affected area
mold and algae easily wash off with some water and a knife
Use DIY Pod Covers to Block Light
After you’ve gotten rid of the algae and mold, it’s extremely important to block any exposed areas that let in light.
You can use pod stickers like these.
I like how stickers allow you to write the names of each plant on them and do double duty as labels. It also looks neat and tidy.
Or, you can do a DIY with aluminum foil. It’s cheap, moldable, and blocks 100% of light.
If you want to make a nice and sleek design, you can 3D print custom lids or covers to match your system.
cover the now-cleaned sponge with aluminum foil so that the indoor garden lights won’t be able to grow more algae or mold
Are Some Indoor Gardens More Prone to Mold & Algae?
The first time I got lots of mold and algae questions, I was really confused.
I never had a problem with either the first couple years of growing herbs and veggies in my apartment.
Then I started to grow a lot more plants, accumulated lots of different systems and tried out indoor gardens from different brands.
… and I started to notice that certain indoor gardens are more prone to mold and algae than others.
Mold & Algae in the Aerogarden
Aerogarden’s indoor gardens are generally very well made.
They include pod baskets, seeds and sticker labels with each of their indoor gardens, so right at setup you’re blocking out most of the sponge from getting enough light.
Without light, mold and algae have a hard time growing.
Their latest garden, the Harvest 2.0, was specially redesigned to prevent algae and be easier to clean.
At first I didn’t like the changes, but now that I’ve used the Harvest and Harvest 2.0 side by side for a year, I prefer the Harvest 2.0!
It has a thicker grow deck made of one piece of sturdy plastic.
The older Aerogarden models have grow decks made of two pieces of plastic, so that water can circulate around each pod opening.
It’s not really necessary, since the water pump is strong enough to oxygenate everything in the bowl, and the streamlined one-piece grow deck is so much easier to clean.
the grow deck of the original Aerogarden Harvest (top left, light blue) compared to the Harvest 2.0 (bottom right, black). The Harvest is made of two tight-fitting pieces so that water can pour from little spouts to the top of each opening whereas the Harvest 2.0 is one thick piece of plastic. I like the Harvest 2.0 design better because it’s easier to clean and reduces algae growth.
I also like that Aerogarden’s fancier models allow you to customize the pump.
The default timer runs for 5 minutes every hour on the smaller models, but with my Aerogarden Farms I can set my own schedule.
For larger plants, I’ll run the pumps longer and more frequently, which improves plant health and yield!
One product I hope they do redesign though, are the Aerogarden’s aerovoirs.
These are extra water tank accessories that you can add to each garden and I find that they easily get overrun with algae.
Both the tubing and water tank are made from a see-through, light blue plastic.
Read more: Reviewing the Aerogarden Aerovoir
adding extra water tanks cuts down on maintenance and essentially doubles the capacity of each indoor garden!
Since the water tanks are placed directly next to the garden, light from the indoor garden panels shines directly over the aerovoirs and has turned the inside of many green with algae.
The tanks can’t really be taken apart.
So unfortunately, a couple of my aerovoirs have accumulated quite a bit of algae – no matter how many times I rinse them out with soap or distilled white vinegar!
I know some people sew their own covers to place over the aerovoirs.
If anyone has tips for removing algae inside the aerovoir, let me know please!
Mold and Algae in the Click and Grow
Unfortunately, I find that Click and Grow’s gardens are one of the most prone to mold growth.
Click and Grow’s smart gardens are designed to use the wick method, a passive form of hydroponics.
While this makes them extremely low maintenance, it also leaves them more at risk of developing algae and fuzzy white mold.
For example, there’s no pump in the reservoir, so water sits still.
And, nutrient beads are embedded within the the company’s proprietary sponges. So each sponge is sitting in water and has nutrient close at hand.
the 3/4 lid design on Click & Grow’s gardens and the nutrient beads in their sponges seem to make them more prone to mold
Then there’s the design of the pod covers.
Each cap is only 3/4 of a circle. Instead of fully covering the tops of each sponge, there’s a sliver that is exposed to light.
I noticed that mold and algae grow directly on this exposed patch of sponge.
While Click and Grow’s indoor garden design could use some small improvements, it’s not a big deal!
I simply add a small square of foil to each sponge, underneath the pod cover, and that prevents algae or mold from forming.
Mold and Algae in the Lettuce Grow
When I got the Lettuce Grow farmstand, I was curious if the vertical tower would also suffer from a persistent mold and algae problem due to their cup design.
The Farmstand has these open slotted cups, with no cover at all!
I honestly was pretty shocked and wondered if the open cup was due to the fact that I didn’t order seedlings through the company.
So I preventatively added foil to each of the transplants I placed in the tower.
Foil, while inexpensive and easy, can also be a bit flimsy.
Over time, a lot of the aluminum foil covers I made fell off and the plants in the Lettuce Grow sat completely exposed.
Surprisingly, I haven’t had any algae or mold growth!
I think it’s a combination of the plants that I’m growing as well as the glow ring design.
Lettuce Grow’s LED lights are built in ring format, like planetary rings circling in orbit.
They don’t sit directly over each plant sponge so there’s not as concentrated a light source as there is with my other indoor gardens.
I haven’t noticed any mold or algae issues using the Lettuce Grow tower
And, the garden tower utilizes an aeroponic design, where the nutrient water is sprayed over the plant roots on a timed schedule (approximately 15 minutes every hour).
So for the most part, the roots free float in air.
This gives them a lot more oxygen compared to plants grown in a countertop hydroponic system.
I suspect that without constant moisture, it’s harder for algae and mold to have the food and dampness that they need to thrive.
Overall, preventing mold and algae in hydroponics is pretty easy.
It just takes a little awareness and a few proactive steps! Keep the light off your water, give your plants good airflow, and stay on top of cleaning.
Your herbs and veggies will thank you with faster growth and fewer gross surprises :)
Having other issues with your indoor gardens? Drop a comment! I’m happy to help troubleshoot your setup! 🌱💧
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