What do you think of when you hear the the word “hydroponics”? Many people think of elaborate growing systems, with pumps and tubing for fluid circulation and overhead lights to simulate sunlight. Also, all those pumps and lights require lots of electricity, and the lights get really hot so you need to install ductwork for proper venting of the room and maybe an air conditioner. If you’re a large-scale commercial grower, all this work and expense may be worth it, but for the casual home grower just looking to have some fresh lettuce and herbs on hand, there is a much easier way to go.
We will be focusing on a simpler method of growing called Bucket Hydroponics, also known as Kratky Hydroponics or the Kratky Method. This is a simple method in which plants sit in a bucket of non-circulating hydroponic fluid (a blend of water and fertilizers). Over time, the plant utilizes the hydroponic fluid and the leaves grow bigger, while the roots grow deeper into the bucket and the fluid level in the bucket drops. Eventually, the roots will grow all the way to the bottom of the bucket, and the hydroponic fluid will be entirely used up. The plant will probably be ready for harvesting long before this point though.
To start with, you will need a container, such as a bucket. I recommend starting with a brand-new black plastic bucket. These can be found online or at any hydroponics store. The best plastic to use is HDPE, marked with a #2 on the bottom. Other acceptable plastics are marked #1, #4, or #5. Avoid plastics marked #3, #6, or #7, since these are not safe for growing food. Make sure the bucket is clean, and hasn’t been used for storing chemicals or paint. The bucket does not necessarily have to be black, but most light-colored buckets will let in light, allowing algae to grow in the hydroponic fluid. If you use a non-black bucket, be sure to wrap it completely in foil or even paint the outside to keep all the light out.
How big should the bucket be? That depends on what you want to grow. Lettuce will use about 1 gallon of fluid per plant, so I use a 3.5-gallon bucket for 3 lettuce plants. You could even use a small 1-gallon container for 1 lettuce plant. Basil uses a bit more fluid, so I grow 3 basil plants in a 5-gallon bucket. Fruiting plants such as cucumbers and tomatoes use a lot of fluid, so I grow those in 32-gallon Rubbermaid Brute garbage cans. These Brute cans are grey, but the plastic is so thick that no light can get in. If you are growing inside, it is a good idea to place your 3.5- or 5-gallon bucket inside another empty 5-gallon bucket, so if you ever have a leak you won’t ruin your flooring. Let’s focus on using the 5-gallon bucket for now.
The plastic lid now needs to be modified to hold the plants. I use 2-inch plastic net-pots to suspend the plants on top of the buckets, so we need to cut 2-inch holes in the lid. The best way to do this is with a drill and a 2-inch hole saw. This will cut a perfect circle in the plastic, and allow the net pots to sit flush without letting in any extra light. I do not recommend cutting the lids by hand, since the plastic is too thick to cut cleanly.
You can cut 1 hole in the center of the lid, which works well for plants that get big and use the whole 5 gallons, or you can cut 3 holes into the lid for smaller plants. After cutting the holes, I like to paint the black lids with 2 coats of white paint to prevent them from getting too hot in the sun. Why not just use a white plastic lid? Because they let too much light through.
Alternatively, you can buy a lid for a 5-gallon bucket with a mesh net-pot already designed into the lid. However, these net-pots are much larger than I normally use, coming in 6-inch, 8-inch, and 10-inch sizes. I prefer to modify my lids to use the 2-inch net-pots, since these are suitable for growing almost everything. However, the bigger net-pots may be useful in certain applications, such as growing root vegetables.
I recommend starting your plants from seed, instead of buying seedlings from a nursery. Seeds cost pennies, plants cost dollars. To get started, get some 1.5-inch rockwool cubes, such as the Grodan A-OK Starter Plugs. These cubes fit perfectly inside the 2-inch net-pots. The cubes come in a sheet, so separate the individual cubes using scissors. Slide the rockwool cube into the net-pot, and rinse thoroughly under running water to remove any residue. Next, place a few seeds (2-4) into each the hole in the top of the rockwool cube. Sometimes a seed won’t germinate, so putting a few seeds into each rockwool cube assures that you will have at least one seed that germinates. You can always thin out the plants later if too many seedlings pop up.
Place the net-pot into a small, shallow container and moisten the rockwool with a dilute blend of fertilizer (1/4-strength). Don’t use full-strength fertilizer at this step, it is too strong for the young plants. I use Dyna-Gro Liquid Grow 7-9-5 for this step (diluted 1/4 tsp per gallon of tap water), but most complete liquid fertilizers will be fine for this step, or you can even dissolve a dry powdered fertilizer. Whichever fertilizer you choose, make sure that the primary form of nitrogen is nitrate (not ammoniacal or urea, since these types of nitrogen are not suitable for hydroponics). For example, don’t use Miracle-Gro All Purpose Plant Food since this fertilizer does NOT contain nitrate as its primary form of nitrogen. Pour the diluted fertilizer gently into the container until the fluid level is about halfway up the side of the net-pot. Don’t pour directly onto the top of the cubes, since the seeds can splash out. Cover the container with plastic wrap and set it aside.
It will take about 2-7 days for your seeds to germinate. Once you see the seedling starting to emerge from the rockwool cube, remove the plastic wrap and provide the plant with light. You can set the small container in a window that gets direct sunlight, or else put it under an indoor light. If you use a fluorescent bulb, you need to have the plant right under the bulb, no more than a few inches away. Ideally the plant will get at least 12-16 hours of light per day. If the plant is not getting enough light, or if the light source is too far away, the plant will let you know since it will get very ‘leggy’ as it tries to reach for more light. These plants will be weak and unable to stand up on their own, so make sure you can provide enough light. Check out the Lighting page for more info.
Once the plants have germinated, all you need to do is make sure that the rockwool stays moist by occasionally adding more diluted fertilizer. If the plants are in a sunny window, there will be a good deal of evaporation, and you will need to add fluid every few days. Don’t let the rockwool dry out! After about 2 weeks or so, when you start to see roots emerging from the bottom of the rockwool cubes, it is time to install the plants into the 5-gallon bucket.
You have many options when it comes to fertilizers. Lots of formulations will work well. There is much more information on the Fertilizers page. As mentioned above, make sure that the fertilizer lists nitrate as the primary nitrogen source (don’t use Miracle-Gro). Here is my protocol for making up 5 gallons: First, I put about 2 gallons of water into the 5-gallon bucket. I use tap water, but there are other water options; learn more at the Water Quality page. Then stir in 1 mL (1/5 tsp) Dyna-Gro Pro-Tekt. This is a liquid silicon supplement reported to make the plants stronger, it is optional. Next, I use 3 empty half-gallon plastic juice jugs to shake up the following 3 dry fertilizers : 10 grams Masterblend Tomato Fertilizer 4-18-38, 10 grams calcium nitrate, 5 grams magnesium sulfate (Epsom Salt). If you don’t have a gram scale, you can get it close by using the fact that 1 teaspoon (tsp) will weigh about 5 grams. You may need to order the Masterblend and calcium nitrate online, but the Epsom Salt is easy to find in your local drugstore. Add some water to these jugs and then shake like crazy! It takes a lot of shaking to get these powders dissolved. (I recommend not adding the powders directly to the 5-gallon bucket, because stirring by hand will not easily get them dissolved, you must use vigorous shaking. Unless you are using a drill mixer, which might work OK.) Once the fertilizers are dissolved, add them to the 5-gallon bucket. Next, add water to within about 4-6 inches of the top of the bucket and stir well.
As an alternative to using powdered fertilizers, you could use multi-part liquid fertilizers, such as Jungle Juice Grow, Micro & Bloom. I have done a head-to-head comparison of the liquid Jungle Juice to the powdered Masterblend fertilizer in this post, and I found that my lettuce leaves and roots looked about the same with both types of fertilizer. Keep in mind that liquid fertilizers are often more expensive than the dry fertilizers.
Now you must check the pH of the solution. You will be targeting around 6.0-6.5 pH units. You can buy a fancy pH meter, but I just use the General Hydroponics pH Control Kit for this. You just fill up the supplied tube halfway, add 3 drops of test solution, and look at the color. If it’s golden yellow, you’re all set. If it’s green or blue, the pH is too high, add some pH Down. And if it’s orange or red, the pH is too low, add some pH Up. In my case, I make my solution using Southern California tap water, which comes out of the tap at pH 8.0. After adding my fertilizers, the pH reads about 7.0-7.5. For 5 gallons, I usually need to add 5 mL (1 tsp) of pH Down to get my pH down to about 6.0. Everyone’s water supply is different though, so be sure to check your own pH.
Finally, move the bucket to its final location prior to completely filling it, since it will be harder to move the full bucket without spilling the fluid (a full 5-gallon bucket weighs about 40 pounds). The bucket should be located directly under a strong artificial light, or in a spot that gets direct sunlight. Ideally the plants should get about 12-16 hours of light per day. Put a lid onto the bucket and insert an empty net-pot, then add water until the level is about halfway up the side of the empty net-pot. This should result in the water level being about 1-2 inches from the top of the bucket. Take off the lid, stir the solution gently to make sure it is mixed, then put the lid back on. Transfer your plants into the bucket lid, and you’re done!
If you are growing your plants indoors, you may want to provide a small fan to circulate the air in your growing space. Learn more on the Air Flow page.
Depending on the plants you are growing and the container size you have chosen, there may be no ongoing maintenance at all. For instance, 1 lettuce plant will use about 1 gallon of water, so as long as your container contains at least 1 gallon per plant, you will be fine. In the case of larger, thirstier plants such as tomatoes, you can start with a larger container, but it still might not be big enough. You may need to add more hydroponic fluid as the season goes on.
For instance, I once grew a Sungold tomato plant that had used 75 gallons of hydroponic fluid by the end of the season. I started growing this plant in a 32-gallon bucket, and every week I would slightly tip the bucket to check the fluid level. After about 2 months, I could feel that about 75% of the hydroponic fluid had been used. Peering inside the bucket, I could see a huge root system, extending down to the bottom of the bucket. To prevent the bucket from running dry, I began adding 5 gallons of fluid to the bucket every week or 2, until the season was over. Why not just refill the bucket all the way back up to the top? This is not a good idea, since the upper area of that huge root system is exposed to humidified air within the bucket, and submerging those roots in fluid tends to ‘drown’ the plant. I have found that refilling up to 1/4 of the container volume is acceptable, since it doesn’t drown the roots too much.
In another example, I often grow 3 basil plants per 5-gallon bucket. I harvest the leaves on a regular basis, and these plants seem to keep growing for many months. Basil doesn’t use the hydroponic fluid at a very high rate, but after 3-4 months the fluid level starts to run low, so adding 1 gallon every 1-2 weeks keeps the plants going strong. If this level of ongoing maintenance is not appealing to you, you could just grow 1 basil plant in a 5-gallon bucket, or you could grow 3 plants in a larger container.
If you grow large, vine-like plants like tomatoes, cucumbers or squash, you may want to prune and tie your plants to keep them growing vertically. Left unchecked, cucumbers and tomatoes will spread out horizontally, so to save space and keep the growth orderly, you can place a support structure around your bucket, and tie the plants to the structure using flexible garden tape. Learn more on the Support Structures page.
Finally, if you are growing outside, keep an eye out for pests and diseases, and treat the plants as needed. For more information on the pests and diseases, visit the Inside vs Outside page.
Once your plants have been harvested, it is time to clean up and reset the system. If there is any remaining fluid in the bucket, it will have a high concentration of leftover nutrients. I usually add some water to dilute this fluid, and then pour it on my outside landscaping plants. The bucket, lid and net-pots should be cleaned using dish soap and a soft sponge. There will likely be a dried nutrient residue on the inside walls of the bucket, which can be difficult to remove. Just gently wash the bucket, don’t scrub. Excessive scrubbing, especially with the rough side of your sponge, can scratch the plastic.
If you would like to completely sterilize your growing equipment, you can clean it with a dilute solution of bleach (1 tbsp bleach per gallon of water). Make sure all surfaces are in contact with the bleach solution for at least 2 minutes, and then rinse thoroughly. I don’t usually find it necessary to sterilize my equipment, but I would do so if I ever felt that I was having a problem with some sort of contamination.
Here are links for vendors that I have used in the past. I have received no compensation from any of these vendors.
Buckets and Lids: Miramar Hydroponics
Glass Jars, 1/2-gallon: Ace Hardware (jars), Ace Hardware (lids)
Net-pots, 2-inch: Miramar Hydroponics, Amazon
Hole saw, 2-inch: Home Depot, Amazon
Rockwool cubes, 1.5-inch: Miramar Hydroponics, Amazon
Dyna-Gro Liquid Grow Fertilizer: Amazon
Dyna-Gro Pro-Tekt Supplement: Amazon
MasterBlend 4-18-38 Fertilizer: Morgan County Seeds
Calcium Nitrate: Morgan County Seeds, Amazon
Magnesium Sulfate: Morgan County Seeds, CVS, Walgreens
pH Control Kit: Amazon
Seeds: Baker Creek, Botanical Interests, Bountiful Gardens, Johnny’s, Kitchen Garden Seeds, Osborne, Park Seed, Seeds of Change, SeedSupreme, Urban Farmer