Floating net pots are a simple and affordable way to grow plants hydroponically, suspending roots directly in nutrient-rich water. Here are several methods using common materials.

What you need to know first

Floating net pots work by holding a plant in a mesh or perforated container that sits at the water surface, allowing roots to hang freely into the solution below. They are ideal for lettuce, herbs, spinach, and other leafy greens.

Method 1 – pool noodle + solo cup

This is the most popular DIY method. Inexpensive, fast, and effective.

Materials

• Pool noodle (foam)
• Plastic Solo cups or small yogurt containers
• Knife or hole saw
• Drill or skewer for drainage holes

Directions

1. Cut the pool noodle into 2 to 3 inch thick rings.
2. Trace the bottom of your cup onto the center of each noodle ring.
3. Cut out the traced circle so the cup fits snugly through the hole, resting at the rim.
4. Use a drill or heated skewer to poke 8 to 12 small holes in the bottom and lower sides of the cup.
5. Fill the cup with growing medium such as hydroton, perlite, or rockwool.
6. Place your seedling or seed in the cup.
7. Set the noodle ring with cup into your reservoir so it floats freely.

Tips

• The cup should sit so its bottom third is submerged in the nutrient solution.
• Pool noodles are buoyant enough to support multiple cups if you cut a long section.
• Use colored cups to block light and prevent algae growth on roots.

Method 2- foam board raft with net cups

This method creates a full raft system, great for growing multiple plants at once.

Materials

• 1 to 2 inch thick foam insulation board (pink or blue board from a hardware store)
• Plastic net cups (2 or 3 inch, inexpensive in bulk)
• Hole saw or sharp knife
• Ruler and marker
• Waterproof tape, optional for edges but recommended (waterproof patch and seal tape, roof seal tape, flex tape (thick version), HVAC foil tape)

Directions

1. Cut the foam board to fit just inside your reservoir or tote bin, leaving a small gap around the edges for airflow.
2. Mark evenly spaced hole positions across the board, spacing plants 4 to 6 inches apart for herbs, 8 to 10 inches for lettuce.
3. Use a hole saw or knife to cut holes slightly smaller than the lip of your net cups so they rest securely without falling through.
4. Sand or smooth any rough edges so the foam does not crumble into the water.
5. Insert net cups into each hole.
6. Fill cups with growing medium and add seedlings.
7. Float the raft on your nutrient solution.

Tips

• Seal foam edges with waterproof tape to extend the life of the raft and prevent foam degradation.
• Label each hole position to track plant varieties.
• This method works beautifully in a large storage tote or plastic bin.

Method 3 – recycled plastic bottle floats

A zero-cost option using items you already have.

Materials

• Small plastic bottles (water bottles, condiment bottles, etc.)
• Larger plastic bottle or container for the float ring
• Scissors or craft knife
• Zip ties or waterproof tape

Directions

1. Cut the bottom third off a larger plastic bottle to create a cup shape.
2. Poke or melt small holes all around the bottom and lower sides for root passage.
3. Cut a separate plastic bottle in half lengthwise and seal the ends to create a float ring, or use a sealed empty bottle on each side as pontoons.
4. Attach the cup to the float using zip ties or waterproof tape so it hangs centered and level.
5. Fill the cup with growing medium and add your plant.
6. Place in your reservoir.

Tips

• Use dark or opaque bottles to prevent light from reaching the roots.
• Rinse all bottles thoroughly before use.
• This method is great for experimenting before investing in materials.

Method 4 – large floating planter for 12 to 18 inch containers

This method is designed for larger plants like tomatoes, peppers, cucumbers, dwarf fruit trees, or large herb clusters that need more root space and structural support.

Materials

• 12 to 18 inch plastic nursery pot or fabric grow bag with rigid rim
• 2 inch thick foam insulation board, cut into a collar or ring shape
• Drill with 1/2 to 3/4 inch spade bit or hole saw
• Waterproof foam sealant or aquarium-safe silicone
• Zip ties or nylon rope for securing the foam collar
• Large reservoir such as a stock tank, IBC tote, large Rubbermaid bin, or kiddie pool
• Aquarium air pump and airstone (strongly recommended at this scale)

Directions

1. Cut a ring of foam insulation board wide enough to surround and support the outer rim of your 12 to 18 inch pot. The ring should be at least 4 to 6 inches wide all around to provide enough buoyancy for the added weight.
2. Trace the outer diameter of your pot onto the foam and cut the center hole so the pot sits through it and rests at the rim, similar to how a smaller cup sits in a pool noodle ring.
3. Drill 20 to 30 holes, each 1/2 to 3/4 inch wide, across the bottom and lower 4 inches of the sides of the nursery pot to allow root passage and water circulation.
4. Seal the cut foam edges with waterproof foam sealant or wrap with waterproof tape to prevent foam degradation and crumbling into your reservoir.
5. Secure the foam collar to the pot rim using zip ties or nylon rope threaded through small drilled holes in the pot rim, ensuring the collar cannot shift or slip off.
6. Fill the pot with a lightweight growing medium such as hydroton, perlite, or a perlite and coco coir mix. Avoid heavy soil as it will compromise buoyancy.
7. Plant your seedling or transplant into the growing medium.
8. Lower the assembled planter gently into your large reservoir. The foam collar should keep it floating with the bottom quarter to third of the pot submerged.
9. Connect your air pump and airstone to oxygenate the water, which is critical at this scale to support larger root systems.

Tips

• Use multiple layers of foam glued together with waterproof adhesive if a single layer does not provide enough buoyancy for the pot size and plant weight.
• Fabric grow bags work well for this method because roots can easily penetrate the fabric walls in addition to the drilled holes.
• Stake tall plants like tomatoes or peppers using bamboo canes inserted into the growing medium and tied to a trellis or overhead support, as the floating base will not support the lateral force of a top-heavy plant on its own.
• For very large reservoirs like stock tanks, consider adding a second foam ring on the outside of the first for extra stability and buoyancy.
• Change or top off nutrient solution every 7 to 10 days at this scale since larger plants consume water and nutrients more quickly.
• This setup works beautifully outdoors on a large property during Minnesota summers from late May through early September.

Best growing mediums for DIY net pots

(see special section below for koi and other fish water)

• Hydroton (expanded clay pebbles), rinse well before use
• Rockwool cubes, soak in pH adjusted water first
• Perlite, lightweight and excellent drainage
• Coco coir, retains moisture well
• Gravel, a free option if you have it, rinse thoroughly

General tips for all methods

• Keep your nutrient solution pH between 5.5 and 6.5 for most plants
• Change or top off your reservoir every 1 to 2 weeks
• Cover your reservoir to block light and reduce evaporation and algae
• Start seeds in a damp paper towel or rockwool cube before transferring to your net pots
• An aquarium air pump and airstone will oxygenate the water and dramatically improve root health

This is a wonderfully satisfying project that can be done with very little money and produces results quickly. Lettuce and herbs can go from seed to harvest in as little as 3 to 4 weeks in a floating system, and larger plants in a 12 to 18 inch floating planter can produce abundantly through a full Minnesota growing season.

Koi and floating planters

Koi and floating planters are actually a natural pairing. This is essentially a form of aquaponics, where fish waste provides nitrogen-rich nutrients that feed the plants, and the plants in turn help filter and clean the water for the fish. It is a symbiotic system that has been used for centuries in various forms.

What works well together

• Floating net pots with leafy greens, herbs, and water-tolerant plants thrive on the nutrients koi produce
• The plant roots act as a natural biofilter, pulling ammonia and nitrates out of the water
• Koi love nibbling on roots that dangle into the water, which can actually stimulate more root growth
• The shade from floating planters helps regulate water temperature and reduces algae blooms, both of which benefit koi

Important considerations

• Do not use synthetic hydroponic nutrients in a with fish. The fish provide all the nutrients needed.
• Avoid any fertilizers, pesticides, or treatments that are toxic to fish
• Koi can be aggressive root nibblers. If they eat too much of the root mass your plants will suffer. A light mesh barrier around the root zone can help.
• Keep floating planters to no more than 30 to 40 percent of the pond surface so the koi have open water and adequate oxygen exchange
• Make sure your pond has good aeration since both fish and plant roots compete for dissolved oxygen

Best plants for koi pond floating planters

• Lettuce, especially loose leaf varieties
• Watercress, which loves the wet environment
• Mint, very vigorous and koi tend to leave it alone
• Kale and Swiss chard
• Nasturtiums, edible flowers that trail beautifully
• Water celery, a natural pond plant that does exceptionally well

Plants to avoid near koi

• Anything treated with pesticides or systemic insecticides
• Tomatoes and peppers, which prefer more controlled nutrient levels than a koi pond provides
• Any plant that drops large amounts of debris into the water

Grow medium considerations for koi pond floating planters

Choosing the right growing medium is critical in a koi environment because whatever you use will be in direct contact with the water your fish live in. The rules are different here than in a standard hydroponic setup.

What to avoid

• Hydroton (expanded clay pebbles) can be used but must be rinsed extremely thoroughly. The clay dust that comes off unwashed hydroton will cloud your pond water and stress your koi.
• Rockwool should be avoided entirely in a koi pond. The fibers can break down and irritate fish gills.
• Perlite is too lightweight and will escape the net pot and float freely in the pond, creating a mess and potential gill irritation for the fish.
• Any medium treated with fertilizers, wetting agents, or chemicals is a hard no around koi.

Best options for koi pond use

• Lava rock is one of the top choices. It is porous, pH stable, fish safe, and beneficial bacteria colonize it readily, boosting your pond biofiltration naturally.
• Rinsed pea gravel works well for heavier plants and is completely fish safe.
• Coconut coir wrapped around root balls and secured before placing in net pots can work, but loose coir will cloud the water so it needs to be fully contained.
• Aquatic plant soil topped with pea gravel, used the same way as a lotus container setup, is excellent for plants that prefer soil over an inert medium.

General guidance

• Whatever medium you choose, rinse it aggressively until the runoff water runs completely clear before it goes anywhere near your koi
• Heavier mediums like lava rock and pea gravel also help stabilize your floating planters so they do not tip in wind or when koi bump them from below
• Beneficial bacteria will colonize your grow medium over time, which actually improves your pond water quality as the season progresses

©2026 Suzy Mottet bloomhearty.com writing, creation, and design