Introduction: Hydroponic Lettuce Garden From Plastic Bottles (Grow Bottles)

About: I'm a biologist, and a professional geek. I can't believe they pay me to do science!

I have no land to grow a garden, But I do have windows that get plenty of sunlight.  I wanted a compact, low maintenance way of quickly growing lettuce and other small, fast growing plants.

My goals were:

cheap: I'm not looking to spend much money on this project, so cheap is good, and free is better. After all, that's why we're doing it ourselves, right? I got pretty much all my materials from recycle bins at work or other household items. The few things you would have to buy cost less than $10, and provide enough material for many of these bottles.

It's easy: No expensive tools or equipment, no expertise, just scissors, and an "exacto knife" or other sharp pointed blade.

low maintenance. Once you set it up, it requires no watering, no fertilizing,

no electricity: There are no air or water pumps. The roots get oxygen by forming aerial roots above the surface of the water as the water level drops.

The materials are easy to find: anybody, anywhere can find the materials for this project. You can use almost any kind of plastic bottle with relatively smooth straight sides, from 24 oz up to 2 litre bottles and beyond. Water bottles, Soda bottles, fruit smoothie bottles, square bottles, round bottles, whatever. The growth media is made from easy to find products, for $5 you can buy enough to fill hundreds of these bottles. I've also been experimenting with using water from a fish tank as fertlizer, with good results so far.

It works: So far it's been working great. the plants are healthy and are growing quickly. The roots look healthy and are not rotting or showing signs of lack of oxygen. The leaves are nice and green and show no signs of nutrient deficiencies. A hydroponic system should work as well or better than a soil based system, otherwise, what's the point.

It's compact. the smaller bottles take up about 3 inches of a windowsill, and the larger (2 liter) bottles take up only 5 inches, so you can fit several in a window. You can also hang bottles to use the vertical space of the window. I'm still working on an easy way to hang them. When I get it right I'll post that part. too.

Step 1: Materials Needed

Materials needed

A plastic bottle: Any size larger than 23 oz. Large 2L bottles work very well, but smaller bottle work fine for small plants like lettuce. you're only growing these for about a month, so it doesn't need to be huge. Also, the sides must be fairly straight and smooth, especially near the "shoulder". Bottles with lots of grooves or ridges don't work well. I've used round bottles and square bottles, they both work fine. Bottles with slightly thicker and stiffer plastic work quite well.

A Shower Scrunchie: one of those plastic mesh shower sponge thingies. they consist of about 10 feet of mesh, which is actually a hollow tube of mesh folded and tied into a compact shape. One of these is enough mesh to make dozens of grow bottles.

Scissors: nothing fancy.

a knife: a very sharp utility knife or exacto knife with a sharp tip.

aluminum foil: To protect the roots from direct sunlight. I grew one plant for a few weeks without the foil, and it didn't seem to really harm the roots, but they did grow away from the sun, rather than growing straight down like the others. You are also likely to develop a problem with algae if the roots and liquid media is exposed to direct sunlight, and this will quickly consume the nutrients and foul the water. You could probably use something that looks nicer, if that's important to you.

(update: after a few more weeks, the plants without foil around the water reservoir did develop serious algae problems, and were noticeably smaller than the ones that were covered)

tape: regular clear office tape.

Seeds: I'm using lettuce, because it's fast growing, and has a shallow, fibrous root system. Bibb lettuce apparently works very well, although I'm using a red leaf lettuce. Try other things, and let me know how they work. larger plants would obviously require larger bottles. A packet of lettuce seeds contains hundreds of seeds, so you don't need to buy a lot, and share the extras.

Growth media: You could buy ready made hydroponic growth media, but it's expensive. You can easily make growth media from store bought fertilizer and epsom salts, with home made egg shell extract for calcium and micro-nutrients.  A small box of fertilizer costs about $3, and box of epsom salts is about 99 cents. You only use a tiny bit of each, so even the smallest box of fertilizer can make enough media for hundreds of grow bottles. Egg shells are basically free, assuming you eat eggs once in a while. A single egg shell dissolved in lemon juice will be enough micronutrients for several bottles.

Step 2: Start Your Seeds

I started my seeds in plastic egg cartons filled with soilless seed starting mix. I transplanted them to the grow bottle when they had a few real leaves. You could probably just directly start the seeds in the completed grow bottle. This would be easier on the seedlings and would prevent transplant shock.

Don't want to spend money on seed starter mix? take a shovel, trowel, or your hands, and go outside. There's an awful lot of soil out there in the woods, and nobody's going to miss a few handfuls of it. This is slightly cheating if you're a real hydroponic purist, since technically hydroponics doesn't use soil, but I won't tell if you won't

To make the egg carton seed starter, just go buy some eggs, the fancy ones in the clear plastic carton. You'll use egg shells in your growth media, and eggs are tasty, so nothing goes to waste. The plastic carton has three folding sections; two "egg cup" sections that cradle the eggs, and one flat lid. 

Cut the flat lid off, and use it as a tray to hold water. Then poke some holes in each of the egg cups to let water drain out. use the other section of egg cups as a lid, to form a dozen tiny greenhouses. Water it once, plant the seeds, and leave them alone for a week.

Step 3: Cut the Bottle

Cut the top off the bottle about half an inch below the "shoulder" of the bottle. The exact height will vary from bottle to bottle. As long as you cut at the level where the sides are straight, and not the part where the bottle narrows towards the neck, you should be fine.  Leave about half an inch of straight side on the "top" part of the bottle, so that it will grip the sides of the "bottom" when you flip it over.

Trace the line with a marker placed on an object of the correct height, such as a stack of books.

Carefully puncture the plastic with the blade and cut along the line. Go slowly, it's easy to cut a crooked line if you go too fast.

You may want to cut a pull tab on one side, so that you can easily remove the top.

Cut a dime sized air hole (or several) about an inch below the top. This provides air flow to the bottom root chamber. It also allows you to add or remove water once the system is set up. A turkey baster works well for adding water, and you can remove water by simply pouring it out this hole. You can cover the hole with tape for transportation to prevent spills.

Step 4: Cut the Cap

Cut a hole in the cap, but leave the threads alone. Use a sharp exacto knife, and be extreeeeemly careful.

Place the cap upside down on a book, with one edge just a bit over the edge. hold it firmly in place and make sure no part of your hand is under the cap, just in case the knife pokes through too far.

Poke with the exacto knife down through the inside of the cap, at the edge. You'll notice that the blade will cut in one direction.

Keep poking the blade through, about a blade width away from the previous cut, so that the blade cuts back towards the previous slit.

I told you to be careful, so don't come crying to me if you cut yourself. You've been warned.

Step 5: Add the Mesh to the Cap

Take your mesh shower scrunchie and cut the string that holds it together so the whole thing can be unwound.

cut off a bit of the mesh, just a few inches, and stretch it over the mouth of the bottle. Then screw the cap on over that. Cut away the excess.

You should end up with a funnel capped with mesh at the mouth. This will keep the plant and support media from falling into the water.

Step 6: Make the Aerial Root Support Basket

Your plant's roots need support, especially the roots that will be above water. Without support the aerial roots will clump together and won't absorb as much oxygen.

Take the long tube of mesh and tie a knot in one end. pull the knot tight and cut off the excess.

Cut off about 6 inches of mesh, so that you have a mesh bag with a knot at the bottom.

Step 7: Mark Water Level

Put the whole thing together to see how it all fits, and to figure out your water level.

Place the mesh basket around the upside down funnel, so that the mesh hangs loosely, about an inch below the mouth of the funnel. Don't pull it up tight against the funnel, you want some space between the funnel and the root support mesh.

Now press the funnel down into the base so that the mesh basket is held in place between the funnel and the base.

If everything fits together well, mark the side of the bottle at the the level of the mouth of the funnel. The easiest way is to just pour some water in until the mouth of the funnel is just barely touching the water.

Step 8: Make Hydroponic Fertilizer Growth Media.

If you are making hydroponic growth media from fertlizer, here's the recipe I've used, with pretty good success so far.

in 1 L (32 oz) water, dissolve:
1/8 teaspoon bright blue name brand plant food which shall remain nameless.
1/16 teaspoon epsom salts. you can get this at any drug store. Get the plain kind without any aloe or mint or fragrance or other additives.
5 drops egg shell extract (see below)

(second update: I've updated the media recipe to half the strength of the previous recipe. I've been using the half strength recipe (shown above) for a few weeks, and the plants are now large, healthy, and are growing very quickly.)

For calcium and micronutrients we will use eggshell dissolved in lemon juice, which produces calcium citrate, and a bunch of other dissolved elements. This also helps buffer the pH, since growth media tends to get too basic (high pH). Egg shell contains calcium, magnesium, and all the other micronutrients needed by plants, in approximately the right proportions. How convenient!

Take an eggshell, leave the membrane intact, and let it dry. Then crush it as finely as you can, membrane and all. Then dissolve it in lemon juice using these measurements:
1/2 teaspoon of dried powdered eggshell
The juice of half a lemon (about 1 1/2 tablespoons).
Leave it overnight in a covered glass or jar to dissolve. It's ok if it's a bit gritty or some of it doesn't dissolve.
This is enough for 2 L of growth media, so only add half (about 1 tbsp) if you are making a 1 litre batch.

I'm still experimenting with using fish tank water, so I'll post another instructable if that works out. So far so good. In fact, the bottles with fish tank water seem to have more extensive root systems.

(update on fish water)
The fish water experiment had unusual results. the plants grown in fish tank water had very extensive roots, but significantly less leaf growth. I'll have to collect more data to see if this is just by chance or an actual effect of the growth media.

Step 9: Assemble the Grow Bottle

If you are transplanting from seedlings, gently scoop out your seedling with a bit of seed starter meda around the roots and place the root ball into the funnel, and gently press it down into the bottle cap. Remove excess soil if it won't fit. You should only have enough media to hold the stem upright, maybe an inch deep, just enough to fill the bottle cap.

pour a bit of water into the funnel and let it drain out though the mouth (into a bowl or something). This will flush out some of the particles that would otherwise cloud your water. It also helps to flush the roots down through the mesh.

If you are starting the seeds in the funnel, just fill the cap with about an inch of seed starter, soil, sand, or vermiculite and plant the seed. I know that technically starting seeds in dirt, or anything resembling dirt, is not pure hydroponics, but I don't really care. If you are a real hydroponic purist, start the seeds in vermiculite, peat, rock wool or whatever you prefer.

once your seeds or plants are in the funnel, fill the base with growth media up to the line you marked in step 7 and assemble the bottle.

Place the mesh root support bag around the upside down funnel, so that the mesh hangs loosely, about an inch below the mouth of the funnel. Don't pull it up tight against the funnel, you want some space between the funnel and the root support mesh. Now press the funnel down into the base so that the mesh basket is held in place between the funnel and the base.

Cover the area below the water level with foil to block some of the light. I just loosely wrap a skirt of foil and loosely tape it, so I can remove it to check the roots.

Step 10: Care and Feeding

Once assembled, this system should require almost no care at all. You will not need to water or feed it. The shape of the funnel will keep the plants upright as they grow, but you might want to rotate the bottle so they don't lean towards the sun and get lopsided.

The water level should drop once the plant starts consuming water. This will expose the upper part of the roots, which is good. You want the roots to be able to breathe.  The air hole allows just enough air flow for the roots to breath, without letting them dry out. The exposed upper roots will not dry out, because the enclosed air space above the water is extremely humid. You should quickly see this area get fogged with condensation.

let the roots stay submerged until the roots extend through the mesh bag by a few inches. this will ensure that the aerial roots do not cling together.  If the water level doesn't drop fast enough, pour out a bit of water so that the upper part of the roots are above water. the roots should be about 1/3 exposed.

Step 11: Update

OK, so it's been about a few weeks since I posted this project, and it's gone fairly well. When I posted, the plants were relatively young, only about a 10 days old, with three or four leaves. They are now quite large, and I've actually picked and eaten some tasty lettuce.

Here's what I've learned.
  • Algae is the enemy: If light shines on your growth media, it will quickly be overgrown with algae. This will not necessarily kill the plant, but it will quickly deplete the nutrients in the media and slow the growth of your plant. It also looks gross to have a bottle of green goo in your window. So wrap the bottle tightly in foil, top to bottom, including the funnel. You could also probably sterilize the media by microwaving it and allowing it to cool. That will kill most bacteria and algae.
  • Watch your water levels and roots: When the plants get large, they start to consume large amounts of water. In a mature lettuce plant, they can suck up half an inch of water per day. You will need to top off the water level every few days, (I use a turkey baster) or the roots will be left high and dry, and the plant will quickly wilt and die. If you see a plant looking droopy, check to see if the roots are still touching the water. When topping off media, just add water, no need to add new fertilizer unless the leaves are looking yellow, and in that case it's probably best to completely change the media.
  • Half strength media works fine. The media recipe I included is a bit too strong. I've been using a half strength recipe and it's worked well. So for a litre/quart of media that would be 1/8tsp fertilizer, and a tiny pinch of epsom salts (a few crystals), and a drop or two of eggshell extract. I'm going to revise the recipe in the original instructable.