The Cheap Vegetable Gardener

pH needs of plants in soil or hydroponics

Jan 6, 2010 hydroponics, pH, water

With the exception of some of my acid loving plants and flowers I normally do not have to worry much about the pH of my soil.  This is because I have amended my gardens with nutrient rich soils in raised beds over my alkaline clay I get naturally in my area.  This and the fact that due to natural and manmade causes the rainfall is slightly acidic and given the average range for the sweet spot of most edible vegetables (see table below) is 5.8 to 6.0 having your soil slightly acidic this is perfect.

Now when it comes to hydroponics this is entirely different.  My tap water has a pH of around 7.5 and the fluctuation of plant using nutrients and transpiration can cause great havoc on the pH on your hydroponic system.  Now this creates a challenge but also an opportunity to have control with great precision your pH and keep your plants growing in the sweet spot for the healthiest plants and the greatest yields.

So whether you are growing hydroponically, or simply trying to figure out why your Fennel didn’t do so well last year take a look at the table below, hopefully for some hints of what happened.

Recommended pH Ranges of Vegetables/Herbs

How to make a cheap soil moisture sensor – Heavy Duty Version

Nov 8, 2009 cheap, electronics, moisture sensor, water

My original version of my moisture sensor has worked great for me but it did have a couple flaws.  The first issue was construction, though I had great luck on my first attempt though after trying to recreate additional sensors given the small amount of gypsum between the sensor and the probes were so thin it was extremely easy to crack the sensor and I normally have about a 25% success rate on later creations (must have had beginners luck on the first one.

The second issue was durability.  Given we are playing with gypsum and as it is suspended in water it will eventually breakdown and there is very little we can do about it.  Though with my latest changes to my automated grow box which includes automated watering based on moisture content I want to ensure my measurements stay accurate throughout the season.  To help with this I have decided to increase the sensors size and also am using galvanized nails to prevent rusting.  After a few attempts I have come up what I feel is a pretty foolproof method of creating a moisture sensor.

How it works:

There were many questions in the comments in the previous post so hopefully I can clear this up a little here.

Technically a gypsum block measures soil water tension.  When the gypsum block is dry it is not possible for electricity to pass between the probes, essentially making the probe an insulator with infinite resistance. 

As water is added to the problem more electrons can pass between the probes effectively reducing the amount of resistance between the problem to the point when it is fully saturated where the probe has virtually zero resistance.  By using this range of values you can determine the amount of water than exists in your soil.

Parts:

• Plaster of Paris
• 2 Galvanized Finish Nails
• 1/2 inch plastic tubing
• utility knife

Construction:

Take your utility knife and cut the tubing slightly longer than your galvanized finishing nails.  Try to make the cut as straight as possible though it doesn’t have to be completely perfect.

Use your utility knife to cut the smaller plastic tube lengthwise, this will allow easier removal of your soil sensor after the mold cures.

Optional: Make the cut diagonally to prevent a potential vertical fracture line.

If you were very careful on you vertical cuts you can avoid this step, but to completely avoid spilling plaster onto my workbench I drilled four holes slightly larger than your tubing.  I used these holes for support but also to catch any of the plaster in the gaps from you less than accurate vertical cuts.

Being careful that the tubing fits together where you split the tubing vertically, insert the tubes into the holes (or carefully on a flat surface)  Mix Plaster of Paris and carefully fill with to the top.  The friction between the tubing should keep a water tight seal where you made the cut, though if the plaster is a little thin and it appears to be leaking through wait a couple minute for the plaster to setup some and try again, at that time it should not have the viscosity to seep through the very small gap that may be causing the leak.

Take your two galvanized nails and push them through a small piece of wax paper.  You may also allow the plaster to setup for a few minutes and then float the nails in the the plaster.  I like the first method since gravity will help ensure they fall straight down and parallel to each other.  As for spacing, I have done some experimentation with the gaps between the probes and my conclusion was, it doesn’t make much difference.  As long as there is a gap (they are not touching) you should get reliable results.

After allowing the sensor to cure for about and hour remove it from the holes you drilled in the wood.

Gently pull back the plastic tubing and you have a nice clean soil sensor.

Lay them out to dry for 24 hours to cure completely and their construction is complete.

For attaching the wires there are a couple options.  The best would be to solder them to the probes though to do this you need to heat up the nail hot enough to enable a strong solder connection.  My little 15W soldering iron just can’t produce the heat for this so I am option for the wire wrap method.  I take about an inch of wire and strip off about an inch of insulation and tightly wrap around the probe.  Given copper will rust and could be a point of failure you will want to insulate this connection and the probes from the moisture.  A few dabs of hot glue works pretty well.  I am planning on trying liquid plastic, though I am currently out and when I have some on hand I will update with how it went.

How to use it

You can simply hook up a multi-meter and check the resistance though if you want to create anything automated you would need to use an integrated circuit (IC) or a electronics prototyping platform such as Arduino.  By applying voltage to one side of the sensor and using a voltage splitting circuit connected to ground and an analog input you can then measure the voltage making it through the probe.  The higher the voltage, the higher the moisture content of the soil.

Conclusion

The above should give you everything you need to know to create your own soil sensor and how to use it.  This can be used as a soil sensor for watering your indoor plants like I am using it.  This same sensor could be for monitoring your outside soil moisture content to trigger (or preempt your irrigation system) to save some money on your water bill and/or maintain consistent moisture levels in your plants which could drastically improve water sensitive crops such as tomatoes.

Computer controlled grow box Beta 2

Sep 29, 2009 indoor grow box, water

Though I have made some significant changes to the grow box controller, the actual grow box has undergone some minor but important changes over the past few months.

Automated watering

Now I must say this one is pretty darn simple.  Though I will be planning on a slightly more complicated hydroponic setup later I decided to start with a very easy bottom watering technique.  Just take a regular old fountain pump (I went with the cheapest I could find) drop it in a 5 gallon bucket of water and attach a hose long enough to reach your planting tray and plug in the power to the pump to your grow box controller and that’s about it.

To prevent evaporation and algae and little bugs making a home in my nice bucket of water, I added a lid with two holes for the water output and power input.  The power input required me to make a straight cut with a utility knife to ensure a snug fit while not requiring me to cur the AC line to feed the wire through.

I also cut a hole of the same size as the water output on the bucket lid to the grow box to allow the line to enter while still keeping the box closed.

Exhaust fan control

Air circulation is important for plants to be healthy but when the box gets warmer than expected I installed two controlled CPU fans to help regulate temperate as well as one static fan that constantly pushes air from the top to bottom.

I added a 12 volt exhaust fan to the top of the box (pictured above) to help push hot air out of the grow box with another (pictured below) at the lower part of the grow box to push in cold air as needed.  Both of these fans are powered by a 12 volt power wall adapter plugged into the grow box controller.

Heating

Though the computer and lights allow the box to create a comfortable internal temperature, sometimes it needs a little help.  For this I installed a regular old seedling heater to hopefully take a little sting out of the cold floor the seed tray is sitting one.  Like other components this was simply plugged into the grow box controller.

Putting it all together

My previous version was a little sloppily put together with duct/packing tape (lets just call it prototyping).  Though this added some hackiness appear it wasn’t too functional so I added a little strip of wood to support a couple hinges which I created a top which holds the LCD panel.

Upon opening the top you can see the grow box controller and the state of the art 600 MHz PC in all their glory.

As you can see I have still have some cleaning up to do with compress air and maybe a few more zip ties but all in all everything seems to have come together nicely.

Water your plants with authority

Mar 10, 2009 gadget, water

This is only a concept, but I am surprised SuperSoaker has not already released something similar.  Now a gun shaped water nozzle is definitely not necessary or possibly even safe in some neighborhoods but sure to make you more manly while watering your pansies.

design reactor Via Gizmodo

How to make a cheap soil moisture sensor

Mar 4, 2009 cheap, electronics, water

UPDATE: Though this still a great sensor, check this post for the latest version of a more heavy duty soil moisture sensor.

I mentioned in a previous post that my previous soil moisture sensor did not hold up in my automated grow box update, so I needed to make a new one.  After a little research there was the classic science class method of creating a homemade sensor by simply putting two galvanized nails in the soil and measuring the resistance between them.  A major problem with this solution is the soil composition can significantly vary the resistance and keeping the spacing between the nails could be troublesome.

After a little more research I came across the method that has been working well for over 50 years.  This method includes taking two metal probes and inserting them into a gypsum block and measuring the resistance between them.  The gypsum absorbs the water and provides a decent range of resistance and moisture measurement.

Unfortunately I was fresh out of gypsum (sort of), so I looked around the garage and found a good substitute, Plaster of Paris.  Plaster of Paris is created by heating gypsum to around 150 degrees where it becomes calcium sulfate hemihydrate.  After adding water and allowing to dry it magically turns back into gypsum with the added bonus it also has the ability to mold to any shape I could come up with .  On to construction…..

Material required:

• 1 tsp Plaster of Paris
• 1/2 tsp cold water
• Disposable cup for mixing
• wide straw (I used one from McDonalds, but most fast food straws should work)
• 2 small pieces of metal (I used wall hangers, but nails, paper clips, etc will work as long as they can fit inside the straw with room for plaster to form around)

I straightened out one end of both wall hangers the best I could with some needle nose pliers.  I then carefully positioned them approximated 15mm apart, the exact measurement is less important though if you are creating multiple sensors I would recommend making them the same gap to ensure consistency of measurements without having to individually calibrating each sensor.  I then used some hot glue (insulator) liberally at the top and at the bottom just enough to keep it in place during while pouring the plaster and while the mold solidifies.

Now insert your secured metal probes into the straw, ensuring that both metal probes are equal distant from the sides of the straw.  The great thing about the wall hangers is they do this automatically due to their wedge shape at the top.  Once you have them centered apply gobs of glue to keep the probe in place but also to seal any gaps between the straw and the bottom of the straw.  This needs to be water tight since this will be the bottom our your mold.

Prepare the Plaster of Paris according to the instructions on the box.  On my box it said 2 parts mix to 1 part colder water.  Given the small size of the mold 1 tsp of mix and 1/2 tsp of water which gave you more than enough to make one sensor.  I used a bamboo skewer to stir since I would have gotten in trouble for trying to use our new silverware.

Now it is time to pour your mold, depending on how steady your hands are you should be able to pour the plaster right into the top of the straw.  Fill about 1/4 of the length then tap the probe gently to help the plaster settle between the gaps.  Repeat the previous step until the straw is full.  If you have problems pouring you can also dip the skewer into the plaster and scrape it against the top edge of the straw.  This step is optionally but I wanted to give my sensor a little point so I carefully added plaster beyond the end of the straw to provide a sharp point.  Once you are done filling the straw, use your glue gun to secure the probe onto the paper you are working on and allow at least 1 hour to set.

After about an hour you can remove the bottom part of the probe.  Do this by carefully cutting around the diameter of the bottom 3/4 of the straw, along with a lengthwise cut as shown in the lines marked above using a utility knife.  You must be very careful in your cutting going too deep can result in cracking the plaster and you need to start all over.

Allow the plaster to dry for 24 hours and it should be ready for testing.  With my probe it is essentially an insulator dry (beyond what my ohmmeter can measure) and a reading of 957 ohms when slightly damp which was a great range for measuring moisture level in my computerized grow box.

Finally, I attached attach wires to my analog measuring device (in my case a PS2 Controller) and I started getting readings.  At this point you should calibrate the sensor by getting a reading with the probe dry then again when it is full saturated in water.  Ironically, the probe I made was almost exactly specifications as the one I repurposed from a cheap commercial soil moisture sensor so I didn’t even have to modify the constants on the automated computerized grow box software.

Given you can make hundreds of these things with a regular sized box of Plaster of Paris, box of paper clips and a few trips to your favorite fast food restaurant.  The cost of each of these things would be pennies and given the cost of buying a commercial product seems like a very economical alternative.

Cool way to collect rain water – Rain Drops

Feb 7, 2009 cheap, harvest, water

I came across this great new design and thought I would share.  The inspiration is to provide a cheap way of capturing rainwater for developing countries.  This would be a great way to prevent some water bottles from going into landfills but also a space saving way to capture some rainwater without requiring the large footprint or cost that rain barrel(s) can take up.  No word on these going on sale yet, seems to be in the design stage but great idea.

“The RainDrops system simply allows people to adapt standard plastic bottles to an existing gutter system to collect rain water. This changes water storage from the most to the least expensive part of the system. These are much easier to clean and replace than larger storage units. The repurposing of these plastic bottles will also give value to many bottles that are otherwise headed for landfills. Corruption in the water sector is a real problem in many developing countries. The scalability of this system helps to give more power to the communities in need.
Another large benefit to using plastic bottles as a water collection system is that it fits in nicely with the process called SODIS, which uses a combination of the suns UV rays and heat to remove pathogenic microorganisms that cause disease. This process is spreading across many developing countries due to its effectiveness and low cost. “