An Outdoor, Nearly Rainproof, Kratky Tote System with Low Maintenance

 

Kratky is a good method for outdoor growing. Because it needs no power, it can be positioned anywhere where it gets sufficient light. Vining squash and melons can trail out on a patio, rather than in the grass. One problem of growing in outdoor containers is heavy rain diluting nutrient. I began growing tomatoes and peppers in Sterlite 40-gallon totes, one or two plants to the tote. But the lids of these and many totes are recessed. Most of the area of the lid is below the raised rim, so the whole lid becomes a rain catchment, and if net cups are just set in 2” holes in the lid, the rain drains into the nutrient.

 

To prevent that, I designed these with risers that support the net cups above the lid’s rainwater level. I use 2-3/8” grommets. The interior of those grommets fit the outer diameter of 2” Schedule 40 PVC pipe. A short stub of pipe fits snuggly in the grommet.

Most of this report will deal with construction problems, because there are some that I had to deal with, but hopefully, you can avoid most of them.

First, the grommets specify a 2-7/8” drilled home. That is a hole drill size not commonly found in the inexpensive hole saw sets. I bought one on Amazon with mandrel for $14. But the groove around the grommet that grips the wall it passes through is fairly deep, and I found that I could make a 3” hole that would seal just as well, and all common inexpensive hole drill sets have that size, and such a set is very useful and indeed necessary for DIY hydroponics.

 

 

In the grommets I had, that groove is very narrow, 1/16”. The lids of most totes are significantly thicker than that, and it would be difficult to fit the grommet. I found that if I used a rotary tool to bevel the edge of the hole, it helped me get the groove to start slipping over the edge of the hole. Once I was doing that, construction was much easier. Trying to fit the grommets without making that modifications was incredibly frustrating.

I have since found that the grommets are also available with a 1/8” groove, which is likely to fit far more easily. They are more expensive. $5 apiece, rather than $3. Both are on Amazon.

Grommets in the 1/8” groove version.

 

I also learned to use the tool to bevel the outer edge of one end of the short piece of pipe so it could more easily begin to slip through the grommet. Totes got three risers installed. My initial intent was to use the two outer ones for plants and the one near the middle front as an inspection and service port. But I went ahead and used all three for plants on some totes.

It only takes about 2” of pipe for enough to extend above the rain line. I happened to have some 2” black PVC tube, which is why my pipe stubs are not white.

This obviously limits to 2” net dups. But I use 2” net cups for everything and find no problems with larger plants like peppers and tomatoes. So, the Kratky tote’s only rain exposure is the very minor one of what rain could make it through the foliage to run through the medium in the net cups. Rain falling anywhere else will simply accumulate in the recessed lid, prevented from getting inside by the grommets and risers, and can be easily dumped by tilting the lid to prevent mosquito breeding.

Note that the risers will prevent a new seedling that has not had roots descend from reaching the nutrient at first. One way to address this is to insert a cloth wick into the net cup. You can also slide the riser down into the grommet so that the net cup medium can reach nutrient in a full tote.

Instead, I grow my seedlings in a Kratky bucket with several holes in the lid until they send down sufficient roots. That also provides them some indoor protection from wind and sun. When they have sufficient roots, I lead the roots down through the risers. The nutrient starts high enough for them and is allowed to drop to one-third in the usual Kratky way. 

 

This is a finished tote.

 

 

Underside of the tote lid.

Newly started tomatoes.

 

 

The riser idea can be used with any plastic container that has the recessed lid problem of catching rain. Also, even though it has wheels, do not hope to move the tote after is has been filled. It will weight well over 200 pounds and will not budge.

A Compact Shelf Size No-Leak Ebb & Flow System

I like ebb and flow systems, but I wish they were more compact. So I set out to design an ebb and flow system that would fit comfortably on a shelf. I began with two Sterlite 10-gallon totes. Each is 25-3/4” x 18-3/8” x 7-1/8”. I determined to stack them and use the  bottom as the reservoir and the top, filled with LECA, for growing. I wanted them easy to take apart and clean and essentially free from leaks. 

 

The theory of operation in this type of ebb and flow is that the timer turns on a small pump that fills the growing tray through a connector that has a grill protecting it from clay pebbles dropping in. An adjustable riser is set to the desired nutrient depth. Nutrient is pumped up and continuously overflows through the riser and returns to the reservoir. At the end of the timed flood period, the pump stops, and most of the nutrient drains back passively through the pump. A small quantity of nutrient remains, but that is on no consequence. It may actually protect the roots in the event of a pump failure that is not discovered promptly.

In the lid of the lower tote, the reservoir, I made a 2-inch hole in the lid near one end. 

This would be to inspect and service nutrient. The top, then, could sit back far enough to clear this port. I leveled it using 1” Styrofoam.

In the growing tray, I mounted a set of common ebb and flow fixtures, a riser to set depth and a fill and drain connection. These pass through the bottom of the tank. The pump was connected directly to the drain and fill connector with ½” vinyl tubing which fit both the connector and the pump discharge. When held aloft, the pump hangs below the growing tray.

First, I drilled the holes for the ebb & flow kit. 

Then I set the growing tray in place on the reservoir lid and marked the center of the ebb & flow kit holes. 

I installed the kit.

I then made two holes in the reservoir lid. A large hole to accept the pump. And a smaller hole where the overflow riser would drain back into the reservoir. 

I used a 25 watt pump rated at about 500 GPH. This pump did not have such high flow that it could get ahead of the depth riser. If it had, other steps would have been required to limit the flow, but it turned out that the fact that these magnetic drive pumps are capable of very little pressure worked to my advantage. The increasing back-pressure of the nutrient filling the grow tray progressively slowed the flow with the pump intake adjustment near minimum until it was circulating fresh nutrient but draining the overflow just about as I wished.

In my larger ebb and flow trays, I had used an 800GPH pump moving nutrient up from the floor, and I had to use a ball valve to prevent the flow from overrunning the riser and flooding out of the tray.

Some shimming with the foam was required to allow the pump to rest on the bottom of the reservoir and to level the growing tray.

 Depending on your pump size, the tubing may have to be adjusted for length. When level, there were foam shims at front and back between the grow tray and the reservoir. 

 

One nice feature is that, because the reservoir lid is recessed, any leaks at the riser and fill connectors will just collect in the lid and drain back through the service port. The service port is made lightproof using a 2” net cup with a clone collar. The fit is loose enough that leaks can drain into it. The pump power cord can just run under the edge of the lid. So, there are no holes in the body of the reservoir. There have not been any leaks, but because of this arrangement, they cannot escape the reservoir lid.

 I filled the grow tray with LECA just beyond the point where the depth riser would be draining the overflow. 

A test run with water showed that it maintained that depth during the fifteen-minute flood period. 

 

I then added another layer of LECA. This layer is above the flood and stays dry and therefore does not grow algae. 

 

I added nutrient and set the timer to flood for fifteen minutes every three hours. I have learned that beyond three hours, LECA begins to dry, and I want it to retain moisture to protect roots. I left it to cycle that night. The next day, I adjusted pH and planted shallots in one tray and mixed day neutral onions in another. The third will be an experiment in carrots, using Parisienne/Nantes carrots which are ball shaped and hopefully will not be so sensitive to the medium characteristics that caused regular carrots to twist into knots. 

 

The finished unit is about 34” x 18” and about 15” tall. That brings the tops to a good working height under the lights, which supplement the natural light in the greenhouse with its heavily matted clear panels.