Notes from the Farm

"As you sow, so shall you reap . . ."

This aphorism is especially true when it comes to planting vegetable seeds. Because of their small size and irregular shape, it is a big challenge to plant vegetable seeds so that they are well spaced and buried to the proper depth. When seeds are planted too close together crops often do not size up well unless they are thinned by hand, which is very time consuming. Planting too heavily is a waste of expensive seeds. If seeds are planted too shallow or too deep they will not germinate well and much of the effort of planting is wasted. Planting too thinly encourages weeds to fill in the row making weeding more difficult.

While there have been many attempts to solve this problem with mechanical devises, until vacuum seeders were invented, there was no precise way to plant vegetable seeds. Vacuum seeders make it possible to space vegetable seeds very precisely, which has the advantage of increased yields, consistent crop size, fewer weeds, and faster time to harvest.

Unfortunately, precision seeders are VERY expensive and are not designed for the small family farm, so last winter we set out to build our own. This has been a daunting challenge, requiring a number of trials and tribulations, but the results have proven very rewarding. What follows is a brief description of how a precision seeder works and how it was built.

The principle of the vacuum seeder is that a disk with tiny holes in it rotates in front of a tube filled with seeds. The holes are smaller than the seeds so that each seed sticks to the disk by the force of a vacuum but does not go through the hole. Seeds are picked up one by one and are moved around to a place where the vacuum to the disk is blocked. From there, they drop down a plastic tube to a heavy steel sled that cuts a groove in the soil. Each seed falls into the groove and is covered by soil under the sled as the tractor moves forward.

Building all of this from scratch has been a bit of a challenge, but we decided early on that old CDs were perfect for the disks. To start with, they are cheap (free) and plentiful (everyone has a pile of them). They are also easy to drill and stiff enough to hold the vacuum without deforming too much. Since different disks are needed to accommodate each seed size and spacing requirements, having an unending supply was a big plus. The CDs also have a hole in the center that is a little smaller than 5/8 inch which can easily be drilled to fit over a 5/8 inch shaft.

The next challenge was to develop the case that the CDs rotate in. For this, we chose 1/4 inch plexiglas since it was easy to machine on a drill press and could be cut with a table saw. By laminating up three layers, we were able to create a case that would hold the bearings for the rotating shaft, the CD, and the drop spout for the seed. The face plate of the seeder (also made of 1/4 inch plexiglass) holds the seed container, which is made from a 1 1/4 inch PVC pipe set into the face plate on a 45 degree angle.

The next challenge was deciding how to power the rotation of the disks. For a while, we toyed with either getting power from the PTO (power take off) of the tractor or from a wheel on the ground. Both of these approaches would have the advantage of tying the speed of the disk directly to the speed of the tractor, but both had significant mechanical challenges. Using the PTO would require gearing it down from 450 RPM to about 40 RPM and building a chain or belt drive for this purpose, which would be no small feat. Driving the seeder from the ground with a wheel also presented the challenge of building a chain or belt drive mechanism. After some thought, we researched 12 volt motors on the web and settled on a windshield wiper motor available on E-Bay for 12 dollars. This motor has three speeds and can be run in either direction, which makes it ideal for this application. The slowest speed of 40 RPM was just what was needed. Since this invention needed lots of testing so it would work with many kinds of seeds, it was important that the electric motor could be tested on a bench without having to continually run the tractor.

Next it was necessary to get the bearings, shafts and chain drive to tie the motor to the disks. Luckily, there is a bearing shop in our area that had everything and we were soon ready to put it all together on a welded steel frame. The next challenge was building the sleds that plant the seed. These were made of 1/2 inch steel to be heavy enough to create a smooth planting surface by being dragged along behind the tractor.

Finally, we needed a vacuum, which was made by taking the guts out of a 12 volt portable vacuum purchased on E-Bay and using some 3/4 inch PVC pipe to get the vacuum to the back of the disks. Adding a plastic valve made it possible to adjust the vacuum strength, which proved to be important to keep from sucking up too many seeds.

The first field trials were somewhat disappointing. The disks seemed to work well, but the seeds would stop being picked up after a while, especially if they were irregularly shaped like beet and chard seeds. This problem was traced to the 60 degree elbow used as the seed holder, which left a flat spot on the bottom that stopped new seeds from migrating onto the disk. Rebuilding the face plates with a straight piece of 1 1/4 inch pipe at a 45 degree angle solved this problem. The next problem was that the seeds were not being covered by enough soil. Building up the bottom of the sled with a deeper keel took care of this. There was also a problem with the sleds plugging up with soil. This was solved by reshaping the keel so that soil will not build up on it. This is still somewhat of a problem on wetter soils and may require further modification.

The seeder is mounted on the back of one of our antique (1948) International Farmall tractors, which we recently restored. This tractor will idle along slowly in first gear making it easy to match the speed of the tractor to the turning of the disks. With some calculations and field trials, we have been able to get pretty consistent seed spacing appropriate to each type of plant.

While we are still experimenting with the seeder and will no doubt be refining it as time goes on, we are very pleased with preliminary results. Both the beets and spinach that we planted with it germinated well and are well spaced for optimum growth. In our next trials we will be planting parsnips, which have a flattened seed that is very light and needs to be spaced at about 4 inches. Initial tests indicate this will work well, but field trials may prove otherwise.

Having the ability to rapidly plant accurately spaced vegetable seeds is critical to our plan to have an efficient farming operation. Next we need to solve the weed problem. (See article on weeds.)

P.S. Do you have any old CDs that you can spare? I need lots of them to make disks for all different kinds of seeds. Next time you come in to the restaurant, please donate some to the cause! ~ Many thanks, Dan Smith.