The Cheap Vegetable Gardener

How to make a cheap soil moisture sensor

15.6 years ago cheap, electronics, water 112 Comments

Soil sensors can be pretty expensive to purchase but a few minutes and a few cents worth materials around your house you can make your own accurate cheap soil moisture sensor.

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…..

Materials for cheap soil moisture sensor:

• 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 re-purposed 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.

Latticework that Works!

11.3 years ago guest post, pests, rabbits, vegetables, vertical gardening Leave a comment

Lattice fencing has been a go-to tool for gardeners forever. Its classic crisscross or grid structure has remained unaltered since its inception for one reason: it works! And as we all know, if it ain’t broke, don’t fix it.

Indeed, the lattice is the one "fixing" things – it provides privacy fencing for yards, serves as a blank canvas for clinging vines and ivy, helps climbing vegetables to reach new heights, keeps out unwanted critters, and functions as the main building material for decorative arbors, trellises, screens, pergolas and more!

Let’s learn a bit more about lattice by delving into two of its main purposes: vertical gardening and natural pest control.

Vertical Vegetables

One of the wonderful things about the overlapping strips in latticework is the structural support they provide for climbing vines and vertically-growing plants and vegetables.

In the world of trellis climbers, you can’t go wrong with selections such as tomatoes, cucumbers, melons, peas and pole beans.

Once the frost threat passes for your region, lay out your garden in front of your lattice incorporating each plant’s specific spatial needs – this info can be found on the transplant’s nursery container.

After placing each transplant in its specified hole, cover with soil (mixed with compost for nourishment) and water liberally. From here, attach each of the climbers to the lattice by looping a soft piece of twine around the main stem of each plant and tie the loose ends to the lattice.

As the plant grows, the twine will guide the stems to grow vertically against the lattice. As soon as the vegetables ripen, harvest them and enjoy a homegrown bite of your hard work!

Natural Pest Control

Another fantastic use for lattice is as a tool for border control for those annoying animals that threaten to move into your home, completely uninvited. Just take a look around at all of the crawl-space homes surrounded with lattice under-fencing and you will understand the widespread infestation issues that lattice solves in such a lovely manner!

But more to the point is how to keep hungry critters like rabbits and deer from feasting on the fruits (and vegetables!) of your labor: installing lattice fencing is a great way to keep their grubby little paws off your peas and carrots and little hooves away from your rose bushes.

Although a picket fence works well as an exterior border surrounding your entire yard, if it is not at least 6 feet tall it may not thwart all deer, as some can clear that height in a single leap. Rather than installing a completely new fence, consider adding a level of lattice at the top of your existing fence.

Attaching a length of lattice to the upper railing of your fence not only provides the additional height to keep the deer at bay but it also adds texture and interest to your fence and can soften the entire look of your yard if you allow vines or ivy to grow on the lattice. Plus, you are repurposing what you already have which is a great way to save some green for the planet and your wallet!

When it comes to rabbits, here’s a quick tutorial on installing a lattice border around your garden:

You’ll need:

• Wire rabbit fencing, with openings no larger than an inch: Ensure you have enough wire for the length of your entire garden area that is at least four feet wide
• Decorative lattice, in the same length as the wire fencing and at least three and a half feet wide
• Garden trowel

To build your border:

• Use the garden trowel to dig a narrow channel around the perimeter of your garden, approximately 12 inches deep
• Bury the wire rabbit fencing in the trench – there should be 12 inches below the surface and three feet above ground
• Fill in the trench halfway, leaving six inches of space from the surface
• Enclose the wire rabbit fencing with the lattice, burying the lattice approximately six inches deep
• Replace the remaining soil and firmly pack the ground around the new fencing

With this type of border, you have form and function. The decorative lattice masks the presence of the wire rabbit fencing, at least partially, and cursory garden admirers may not even notice it, depending on the style of lattice you choose. By burying the fence in the ground, you discourage burrowing and digging and at three feet tall, even Bugs Bunny will have difficulty breaching your barrier!

What other garden projects do you plan to complete with lattice?

Chris Long, a long-time store associate at a Home Depot in Illinois, writes for the Home Depot website. He enjoys writing on outdoor projects ranging from lattice to lumber and fencing.

How to determine your own personalized last frost date from local weather station

15.5 years ago computer, last frost date 3 Comments

There was a discussion in comments on my previous average last frost post on how to determine an accurate last frost.  A great point was made by Daphne where every garden can have its own microclimate so the date you find online or in a book could be many weeks off for your microclimate in neighborhood.

To be able to predict your last frost date accurately it takes some history, if you have lived in your current residence and happened been capturing your temperature data accurately by memory or paper you may the information to predict your last frost date.

For people that are relatively new to their residence, like myself, I felt there I had very little information to determine an accurate prediction of my last frost date.  This was until I remembered Weather Underground which logs results of schools or private individual that register their weather stations.

After a quick search I was able to find someone who had a weather station in my neighborhood.  After doing a custom query of the full range of the of the weather station, which in my case was a little over 4 years, I had all the information I needed.  By carefully adding a horizontal line at freezing using a graphics program (Microsoft Paint) I could easily see where the low temperature dipped below the freezing mark.

From a quick glance at the data it appears that the first week of April is a pretty safe date for past few years.  But if you look the the irregular low temperatures we have had this month this might be harder than I thought.

Now of course your neighbor may a different microclimate than you, but should get you in a better ballpark than the generic number you find fro your city.  You could always spend $500-$1000 on your own weather station to get some better accuracy, but for me seems close enough to me.  Though the weather station would be a really cool gadget to have.

Best DIY cheap soil moisture sensor

14.9 years ago cheap, electronics, moisture sensor, water 99 Comments

My first version of my cheap soil 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 for cheap soil moisture sensor:

• 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 your cheap soil moisture sensor

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 cheap soil moisture sensor and how to use it.  This can be used as a moisture soil sensor for watering your indoor plants like I am using it.  This same moisture 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 – Part 1

15.7 years ago cheap, computer, electronics, indoor growbox, PC thermometer 96 Comments

The Idea and Design

My PC Grow box was very effective though it did have some shortcomings along with my desire for tinkering caused me to create a new version code named “Project Everbearing” after the test subjects for the project, several Everbearing strawberry plants I propagated from my garden last Summer/Fall.  The specific shortcomings I wanted to overcome were temperature control and limited size.  My grow box has to live in my garage so on cold nights the temperatures can fall low enough to kill my summer seedlings (tomatoes/cucumbers)  Size is an easy fix just make it bigger though it is more difficult to keep a larger grow box warm and still well lit.�

My solution to both of these problems was the addition of a computer to the system.  First computers generate heat, using this along with computer controlled fans and incandescent lights (heater)  allow me to regulate the heat to my desired levels.  This is the point a normal person may have just stopped, but I am far from normal and decided a few more features, which I will explain more below.

The Structure and Insulation

First comes the structure, upon inheriting a set of shelves from my sister, we ran out of room for some of our existing storage shelves (see above), though we used the buckets to store loose toys on our new shelves we had the structure of the old one sitting in the garage for some time.  After many passes by in the garage not knowing what do do with this shell, it finally came to me that this would be perfect for my new grow box, (Reduce/Reuse/Recycle) in action.  The only customization required was the removal of a couple of the wooden dowels and I was ready to add some hardware.  Of course you could do the same thing with an old bookshelf, cabinet or just with construct your own frame with a 12”X1”X8’ foot board cut in two along with two 1”X1”X8’ pieces of lumber cut into two.  Screw one 1”X1” in each corner and should should have a pretty solid frame.  For the top I used pegboard mainly because I bought a 4’ by 8’ sheet when I only needed half of it but worked really good to use zip-ties to secure various components and provides decent airflow between the computer and growing areas.

Second comes insulation, after some not so careful calculations and measurements I determined I could cover the 3 exposed areas with 2 sheets of 2’ by 4’ sheets of insulating Styrofoam.  I glued and taped (duct tape of course) the Styrofoam which was cut using a utility knife and straightedge to cut to size making sure I made the top straight and flush.  I then created an exactly copy of the other side and one more piece for the top.  Using a long strip of duct tape I created a hinge for the top and glued side of the box.  The last piece I simply fit into place using a tool box to ensure a tight fit but also allows easy access to plants when needed.

The Lighting

I went cheap on the lighting taking from the success of the PC grow box I decided to go with a similar setup using $2.00 home depot wired sockets hooked up to an couple old computer power cords.  I went with two 24 watt CFL bulbs and one incandescent bulb.  Though the incandescent is not as efficient and the CLFs it does provide a full spectrum of light and a little extra heat which the box can use in the many times cold garage where it lives.  The CFLs and incandescent exist on two separate circuits so they can be controlled independently by the software.

 

The Software — Grow box brains

Now I know all of this could be done with a Basic Stamp or Arduino pretty easy, but I wanted the ability to track history and have a decent user interface to look at, so I wrote a windows form application using C#.  To cover the basic functionality of temperature control I used the parallel port outputs hooked up to the computer’s parallel port to give the software the ability to turn the lights on and off.  By configuring a “sunset” and “sunrise” time which I am in complete control over the lights will turn on and off as appropriate.  I added some logic to ensure the plants stay at a comfortable temperature (thresholds configurable) by turning on the incandescent bulb when it is too cold and an exhaust fan when it gets too hot.  In order to allow the computer to know these temperatures I used a PS2 controller to create two temperature sensors one for the area the plants are growing and another for the top area where the CPU resides (computer was too old to have onboard temperature sensor)

My daughter thought it would be cool if we have some sort of automatic watering system.  I agreed, so I added a moisture sensor and created an algorithm to periodically check the moisture level and activate a water pump to add water until it reaches the specified moisture level.  I still need to buy and hookup the pump but coding portion is complete and tested.

I live in the Pacific Northwest it rains a lot and can get cold in the evenings and I don’t want to trek out to check on my plants.   solved this by adding the computer to my Wi-Fi network now I can take look at them by connecting to the machine wirelessly and see how they are doing through it’s webcam.  I also take periodic pictures of the plants so I can create cool time-lapse videos of progress like the one below.  I also have the ability to browse through pictures taken at specific time periods.

Finally to store all of this data I installed SQL Server 2005 Express (free) which allows me to track historical data of the conditions and images over time.  If you have data, you definitely need some graphs.  Being too lazy to do this graphic work I leveraged ZedGraph (free) to allow some visual tracking of temperatures and moisture content.

Features for future versions (Beta 2?)

• Finish automated watering
• Add automated red LED lights for flowering stage
• Install LCD Panel
• Make box look better (real door which does not require tape to open/close)
• Create single USB controller for lights/sensors
• Better/additional camera

Video of grow box “booting” up, personally I like the flashing lights when the computer sends signal through the parrallel port.  If you are old enough to ever have a printer that used a parallel port this is when it would make its annoying sound letting you know it was alive.

Updates:

Computerized Grow Box Update #1

Growing peppers at high latitudes

15.4 years ago hydroponics, indoor growbox, peppers 8 Comments

Here in the Seattle area we are, as you say, latitudelly challenged. We are fortunately to have the Pacific Ocean to give us mild winters and summers though our distance from the equator provides our plants with less intense light and a relatively short growing season for summer crops. One in particular difficult summer crop are peppers.

This is important because one of the major exports of my garden are the ingredients to allow me to make homemade garden salsa (tomatoes, garlic, onions, cilantro, jalapeño peppers) Al ingredients come from my garden (except for jalapeño peppers) This year I am determined to fix this.

I have a couple strategies for doing this, the first is to “start early” pepper plants require 80-110 days from seedling to harvest, timing is everything. Given our late winters here over the past couple years, I don’t really have much of a cushion here and would also be nice if the peppers were ripe when the tomatoes are getting red as well. To get a head start many weeks ago I planted several jalapeño pepper seeds and they currently are turning into some great looking pepper plants in my grow box. As they have grown I have potted them up to encourage them to continue to grow vigorously.

Not wanting to put my eggs peppers in one basket, I have decided to try a few different techniques in case one completely fails I hopefully have a couple backups:

1. Grow pepper plant in grow box in WonderSoil
2. Grow pepper plant hydroponically using a Grodan Gro-Blocks
3. Grow pepper plant in the ground beside my tomatoes
4. Grow pepper plant in large pot in sunniest location

I honestly can not really predict the outcome of this experiment. The grow box as the advantage of accurate temperature control but the CFLs though work great can’t compare to full sun. On the other hand outdoors has the great light intensity of the actual sun though given the pepper plants can stop growing lacking 60 degree nights and at least 70 degrees during day. Given we don’t have too many nights greater than 60 degrees the grow box might have a chance.

UPDATE — 05/25/2009

Plant grown in WonderSoil in grow box at temperature controlled to remain above 60 degrees at night and a high of 80 during the day.  This is amazing results compared to the 2.5 inch plants I started with less than a month ago.

Plant grown hydroponically using a Grodan Gro-Blocks also in temperature controlled grow box.

Plant grow in actual dirt outside in good light

Plant grown in pot outside…well this one is already out after some high winds and cold mornings this one was looking pretty bad to I brought to the infirmary (the grow box) to bring it back to life, which seems to have done wonders.

The obvious winner at this point is the pepper plant in WonderSoil in the grow box, though I have noticed some recent growth in the outdoor plant now the weather has started warming up, so might be some time for Mother Nature to redeem itself.  Overall I have been very impressed with the results of the grow box but still need to see if I can get flowers and fruit…until the next update…

UPDATE — 06/20/2009

We were blessed with some warm weather so the outdoor potted plant has been doing great blossoming and almost a dozen of good sized peppers growing.

I have seen plenty of blossoms on the pepper plants in the grow box though I have not have and fruit set.  I have two theories what is causing this, first is we have hat some hot weather with the garage getting over 85 degrees even with best exhaust and airflow it was hard to keep the temperature from exceeding 90 degrees which causes the blossoms to drop.  The second reason is I have been attempting to hand pollinate the flowers with the absence of some nice bees to do the work for me.  I have been using a fine paintbrush without much luck.  Switching to having better airflow and using a Q-Tip to simulate a bees bottom.

The plant I had in the ground eventually got overtaken by a pumpkin plant which I removed and moved to the grow box given it had not shown any significant signs of growth since I transplanted it there.

Right now seems the best method is grow the pepper plant to about 18 inches and just let mother nature take care of things at that point.