Hydroponics

Growing plants without soil.  I knew it from the ’70’s & ’80’s reading Mother Earth News and probably Popular Science, and I thought it was new then, but turns out it’s not. It was essentially “invented” by William F. Gericke at UC-Berkeley in 1929 when he “began publicly promoting that solution culture be used for agricultural crop production.” That’s from the Wikipedia page on hydroponics. In 1940 Gericke published a book, The Complete Guide to Soilless Gardening. (The link is from Archive.org, and the book is out of copywrite so it’s legal to read the pdf.) Fascinating stuff, I’m reading it now.

To grow, plants only need light, water, oxygen, and certain nutrients.  If they can get those nutrients from the water, they don’t need soil.  They do need some kind of physical support though, so an inert media is often used for that.

A simple vertical tower system

There are lots of ways to “do” hydroponics, but the method I want to talk about here is often referred to “drip-ponics” or “spray-ponics.” (Some might call it “aeroponics,” but there are important differences.)  Suspend plants in small baskets inside a chamber and periodically drip or spray nutrient solution (fertilizer) over their roots, as in this drawing:

A submersible pump periodically pumps solution to the top of the tower, where it rains down on the roots of the plants, then drips back into the reservoir to be recycled.

During the drip/spray phase the roots take up nutrients from the water, and they always have access to plenty of oxygen.  It’s this exposure to lots of oxygen that tends to make plants grow better in hydroponics than in soil.

As long as there are no leaks, the only water loss will be as the plants consume it.  They say to change out the solution every 3 or 4 weeks, because the plants do consume some of the nutrients, but I’m usually quite lax about that, and the plants seem to do fine. Just top up the water as necessary. Maybe after a crop cycle or two refresh the nutrient solution.

Timers

This one is ideal and super-easy to use, but a bit expensive.  4.5 stars on 1700 reviews though, really solid device.

Pumps in these systems are run on an “x minutes ON, y minutes OFF” schedule, and this timer lets you easily do that. 

Some say 15 minutes ON, 15m OFF, but I find that to be too much run-time, so I start with 30m OFF, 5m ON, then adjust the ON and/or OFF time up or down as the plants need. This one has a photocell and you can set so it doesn’t run at night, thus saving electricity & wear on your pump.

This mechanical timer would work fine, though its ON times are only selectable in 15m increments.  I’d start with 15m ON and 60m OFF and then see if you need to decrease the Off time or if you can go longer

Whatever timer you use, they’re typically not weatherproof (unless you pay a lot more), so keep it protected from the rain somehow.  A small plastic bin with a lid works well:  notch the rim to pass in the extension cord and pass out the pump cord, set up the timer inside, put the lid on, and maybe caulk the small cable openings.

Holding the plants

Net cups hold the plants in the tower, and are used in a lot of different hydroponics applications.  The ones in this project are 2” diameter, but they come larger and a bit smaller.  The slots and holes allow the roots to grow out into the air space and get lots of oxygen, as well as getting nutrient solution dripped onto them.

We fill those with some kind of media to both support the plants and to hold some moisture between waterings.

The first two are really seed-starting options, both of which I use.  You don’t have to, but they make it easy.  (Growdan is the main brand of the rockwool cubes; they’re cheaper than Oasis cubes.)  Once you have decent-sized seedlings that you’d normally plant out (but I go a little smaller because it’s really stress-free for the plant), pop the cube in a net cup and either that’s it, or add some of the other media. 

People often put a layer of expanded clay pellets (Hydroton is a brand name) in the bottom, then fill up the sides and tops of the net cups with it.  That provides a good bit of weight to anchor the plant, leaves lots of air spaces for the roots to grow into and around, and holds a little bit of moisture between waterings.

I used to do that, but now I like to have more water-holding ability, so I add coco fiber (or coco ‘coir’, buy it on Amazon).  This is great stuff for growing in, you can research it.  I mix in some perlite for aeration, maybe 25% by volume, but you can certainly go up to 50%. 

And I’ve started experimenting with adding a small amount of sodium polyacrylate to the mix, and that stuff holds a LOT of water.  It’s used in diapers to make them super-absorbent, and is what’s in the Hello Fresh freeze-packs if you get those or have a source.  I’ve read that it’s food-safe, but make up your own mind about that.  Right now in August in Atlanta, with my towers on a north-facing deck that only gets sun till noon, my timer is at 2h Off, 3m On.  That’s how much water the supplemented coir mix is holding.

You can even start seedlings in Jiffy peat-pellets if you’re used to those, and pop them right into the net cups.  Peat is mostly inert, but it’s a bit acidic and will lower the pH of your reservoir.  Or if you normally start seeds in seedling mix, just shake most of the mix off the roots and transplant them into the coco.  It’s mostly peat and/or coco, but but a little bit of dirt or organics isn’t going to hurt the system.

Nutrients

   Hydroponic nutrients can get complicated (and expensive), but they don’t have to be in my experience.  You’ll have to do some research and find what’s best for you after the tablets run out, but use:  “Jack’s 3:2:1 recipe” 

   It’s based on a water soluble 5-12-26 fertilizer made by Jack’s Nutrients (JR Peters) that’s a “specific balance of macro, secondary, and micronutrients that delivers an efficient combination of nutrients” for hydroponics  Regular 10-10-10 probably won’t work because it’s not very water-soluble.  A cheaper substitution is Southern Ag 5-11-26 “Hydroponic Special” fertilizer.  If you can’t find or special order it locally, shipping is expensive, but a 25# bag will probably last the rest of your life.

To that you add calcium nitrate for more calcium.

And then Epsom salts (magnesium sulphate) for more magnesium.

  The ratio is 3:2:1 grams each fertilizer:cal-nitrate:Epsom per gallon of water to make a general-purpose hydroponics nutrient solution.  But because you’ll be mostly growing leafy greens and herbs in a system like this, and they’re not as heavy feeders as tomatoes, peppers, etc, I run half-strength solution and it seems to be plenty. 

  So to do a nutrient solution change-out on a 5-gallon bucket, cut the volume in half to 2.5gal, multiply by the ratios, and mix up:  7.5g 5-11-26, 5g calcium nitrate, & 2.5g Epson salts.  Shake that up in a gallon of hot water, then fill the bucket with cold water. That’s what’s in the nutrient tabs provided.

   I keep a jug of concentrated solution on hand, and then dilute as needed as “so-much concentrate to so-much water.”  But if you do that, don’t go more than about 10x concentrated, or the calcium nitrate will react with the magnesium sulphate to make insoluble calcium sulphate (Plaster of Paris).  It won’t hurt anything, but it depletes some of the nutrients and makes them unavailable to the plants.

Other additions to consider: 

Silica in the form of potassium silicate (AgSil 16H is one).  Plants get silica from the soil, but hydroponic plants don’t have that luxury. They don’t absolutely NEED it, but it helps build stronger cell walls and stems, and might provide resistance to disease, notably powdery mildew.

Beneficial  microbes:  Mikrobs brand is one: “Glomus (endomycorrhizae), Bacillus (plant probiotics), Trichoderma (beneficial fungi).”  There’s a whole science there that I barely understand, but plant roots in soil develop symbiotic relationships with these beneficial micro-organisms.  They secrete sugars that the microbes eat, and the microbes in turn break down and transport nutrients to and into the roots.  So even though this is hydro, people say that plants can still benefit from these.  And this is the 2nd big reason I like to use coco coir: besides its water-holding properties, it provides a substrate for these microbes to reside in.  Check this out:

Research from the University of Queensland, Australia.

I don’t know if hydro plants see as much of a boost, since their nutrients are water-soluble and don’t need to be broken down, but some people swear by them, and I figure they can’t hurt.

“Bennies” can also contribute to good root health by crowding out harmful microbes.

Some people make compost tea and add it to their hydro systems to get bennies that way. You can also research doing “organic” hydro by using fish emulsions, kelp solutions, blood meal, etc, but you’re on your own with that. Although “aquaponics” has always interested me and is the ultimate in organic hydro: you grow fish in a tank and use that as a nutrient reservoir for your plants. Hydroponics is such a wide-open field and people are doing tons of different things, just start Googling! Youtube is also a great resource.

Test Meters

If you get semi-serious about hydroponics you should buy an EC meter and pH meter to keep track of the strength and pH of your nutrient solutions. This set is 15.19 after the coupon and has 4.2 stars on 201 reviews. Many others are available.

You should also buy pH Up and pH Down solutions so you can adjust your pH as necessary. Or research other methods for safely raising and lowering pH.

Vertical Grow Tube

I’m using 3″ PVC DWV pipe, which is thin-walled drain/sewer pipe. Don’t buy the thick-walled PVC pipe for carrying water, the walls are too thick to work with. 81″ long. Using the printing on the pipe as a centerline, mark for the first hole 4″ down from the top. Then mark for holes down every 3″, rotating 90° around the pipe, for a total of 21 holes.

At each mark, draw a perpendicular line a little bit longer than the diameter of your net pots. For 2″ pots, lines 2 1/8″ long work well, or you might be able to go out to 2 1/4″. If too short, the holes you’ll make in the next step are likely to tear at the ends of the cut. To minimize this, somehow round the ends of the slots. In metallurgy these sharp edges are called “stress risers,” and are the reason you can ‘cut’ glass. If you’ve ever done that or seen it done you know that the glass is scored with a diamond wheel, then when the plate is bent over that line the glass cracks cleanly; that’s because the groove etched into the glass raises the stress along it, propagating the notch down through the glass plate.

The same holds true for the ends of the notches you cut in the PVC pipe. I have a small 1/8″ round file that I used to round the ends of the slots with. Or you can heat up a suitable diameter of wire or a drill bit and round the ends that way. I’ve tried both and the file is faster, but melting may actually be better. I cut the slots with a power miter saw, but you could do it with a hand saw in a miter box.

At each of these slots you heat up the surrounding plastic with a heat gun, then force a round object into them, forming pockets in it to hold net pots, which you can learn about in this Youtube video (not mine).

Reservoir

I’m using a Lowe’s bucket, like many on Youtube use. Cut a hole in the lid the diameter of your pipe, then figure out a way to anchor the pipe in the center of the bottom of the bucket. I first bought a 3″ cap and tried gluing it to the bottom of the bucket, but no glue I had on hand would adhere to the bucket (not even PVC cement).

So next I drilled a small hole through the bottom of the bucket and through the flat part of the plastic cap, then fastened the two with a small screw with silicone sealant. That worked until the bucket cracked through the screw hole and about 2″ each side. So don’t do that.

So next I cut four short lengths of 1/2″ PVC pipe and used PVC cement to glue those to the outside of the cap, spaced evenly, to center it in the bucket. (Think Christmas tree holder.) Later I modified it to just 3 legs, which is that’s really needed. That works well, but on the system I’m currently building I’m going to try something else that eliminates the need for the pipe cap. Pictures to follow.

Pump

The Vivosun 800 gph, 24W pump for 18.12 from Amazon works well, and has 4.5 stars on 13k reviews. It’s advertised as having 10’ of lift, which is a stretch, but it’s definitely good for 7 to 8′, so it works for this application.  Any similar pump would work, but it must be able to push water to the top of the tube, and not all of these small submersible pond/fountain pumps can do that.  I put the pump in a filter bag (1 gal paint strainer bag from Amazon) to keep debris from the net cups from getting to it.  The pump itself can handle small debris, it’s the emitters/drippers at the top you need to worry about.