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hydroponic seed starter plugs

Pros and Cons of Polymer-Bound Seedling Plugs

Wanted: the perfect media

People have been trying to start seeds in weird stuff for a long time. From gravel to packing peanuts, just about everything has been tried.

The great thing about seeds is that they come pre-packaged in a neat shell with all the nutrients they need to germinate and thrive for the first few weeks of their lives.

This means that the requirements of a seeding material are few. Most seeds require only three things from their media:

  • consistent moisture (but not wetness)
  • aeration (oxygen throughout the media)
  • lack of disease (not recycled from diseased crops)

(Of course, seedlings also require light and warmth, but these aren’t connected to the type of media.)

With these three things, almost anything will do for seedlings—but this doesn’t mean that anything will do for you. Different types of systems and the personal preference of farm managers will determine other characteristics of the seedling media you choose.

For example, you’ll need a media heavy enough to provide stability, but light enough to handle and move. You may care deeply about using sustainable materials, so you want something you can either recycle or reuse. These farmer-specific goals will whittle down your media options.

Recently, flexible or polymer-bound plugs have risen in popularity, especially for systems with recirculating irrigation (like hydroponic systems) and limited space. There are several nice qualities that bring them to the top of the list.

Pro: clean and neat

Polymer-bound plugs incorporate an organic material like peat or coco coir and bind it together with a polymer—picture a rubbery glue. This makes the plug very contained.

Unlike a soil, plain peat, or plugs made of loose media, little bits of material will not break off and clog up irrigation.

Pro: Easy to handle

Polymer-bound plugs are separate from each other, and one piece. This means you won’t have to cut or tear plugs apart, avoiding root damage and saving time.

Handling polymer bound plugs won’t create dense portions in the root zone either, which happens with some media types and causes damage and anaerobic zones.

*This does not mean that you should be handling seedlings a lot! The less they are handled, the fewer disease opportunities there are!

Pro: convenience

Another trait desired by many growers in tightly spaced systems with a need for labor efficiency is that polymer bound plugs can be extremely convenient. Many are shipped already in the seedling tray, and already damp; growers simply pull the tray from the package, adds seeds, and place it into their seedling system.

This saves time sorting plugs (or loose media), filling trays and wetting the material.

Pro: faster germination

Compared to some other types of media, polymer-bound plugs have shown faster germination.

Even a few days can speed up your growing cycle. If you save 2–3 days every turn, you can fit in one extra harvest a year; that translates into more revenue! This could very well make polymer plugs worth the investment, depending on what your current seedling operation is.

Con: hard to reuse

Polymer-bound plugs can’t be reused in the typical sense. Once seeds grow in a plug and are transplanted into the maturing system, roots tend to take over. By the time you harvest the crop and take the root ball out of the system, the plug is too overgrown or torn apart by roots to be reusable.

Growers can reuse plugs in which the seed did not germinate, but this can open doors for disease and is more labor intensive. The final option is composting. Polymer-bound plugs will decompose and compost over time, but it takes 3–4 years for them to break down.

Balancing benefits with cost

Of course, an important factor in choosing the substrate is weighing the benefits gained against the cost. In a comparison between polymer plugs and soil plugs for a small grower, for example, polymer plugs will come in second for initial and recurring costs.

Something that growers must calculate into that is how long it takes them to plant each tray of plugs. If it takes growers 2 minutes longer to plant a tray with soil, that might make up the price distance between the two types.

So which is better?

We’ve used polymer-bound plugs, soil, rockwool, peat, oasis, and more. None is universally best, and growers have many options. But polymer bound plugs are the best for growers who want to run a clean hydroponic system and reduce labor time.

Want more info on hydroponic substrates?

There’s a whole course on substrates (media) and how to choose the best one for your system. Check it out here:

The benefits of polymer-bound seedling plugs have caused a rise in popularity, especially in systems with recirculating irrigation & limited space.

How to make seed starter plugs for less than a penny each.

Gardening season is nearly upon us, and with spring just around the corner, it’s time to start germinating the seeds for this year’s crops.

While there are many different products you can buy for germinating seeds, and all of them work quite well, you can actually make your own from something you normally just throw away…the cardboard tube at the center of a roll of toilet paper.

Standard Toilet Paper Tube

Making starter plugs from toilet paper tubes is super easy and works just as well as any product you could purchase. I’ve used them for several seasons with great success. They are bio-degradable, readily available, take 30 seconds to make, and are virtually free.

Here’s how you make them:

Step 1: Cut the tubes in half

Place the tube on your work surface and flatten it with the palm of your hands, making sure to press the edges to make a nice crease on each side.

Press flat and crease.

Then, using a sharp pair of scissors, cut the flattened tube in half to make two shorter tubes. Flattening the tube first makes it easier to cut.

Cut the tube in half. You’ll have two smaller tubes.

Step 2: Cut tabs into one end

Take one of the tube halves and make a 3/4″ long cut starting at one of the open ends. You don’t have to measure exactly. The finished cut should run about a 3rd of the way up from the end. Cut through both layers of the flattened tube, halfway between the two creases.

Make a cut 3/4″ up from the open end. Finished cut.

Open up the tube, rotate it 90 degrees and flatten it a second time so that the cuts you just made are now on either side, and one of the original creases is now in the center of the tube’s longitudinal axis.

The cuts cuts are now on the left and right sides. The original creased edges are now in the center.

Make an additional 3/4″ cut exactly as you did above, cutting along the original creases.

Open up the tube and you should now have a tiny square box. The four creases you made will be the corners of the box, and the two cuts you made have created four “tabs” which we will fold together to create the bottom of the box. Set the little cardboard box on your work surface so that the tabs are facing up.

The tube should resemble a small cardboard box.

Step 3: Fold the tabs

Starting with any one of the tabs, fold each of the tabs inward and crease it.

Fold and crease each tab.

Work your way around the box until all of the tabs have been folded and creased. Each tab you fold should overlap the previous tab.

The second tab overlaps the first tab… …the third overlaps the second… …and the final tab sits on top.

For the final tab, tuck one edge underneath the first tab. This will lock everything into place and you should now have a box with a closed top.

Tuck one end of the final tab under the first tab to lock them into place.

Step 4: Fill with peat or potting soil and plant your seeds

Flip the tiny box over so that the closed end serves as the bottom of the box. You can now fill the box with peat or potting soil plant your seeds. Use them the same way you would use any commercial plugs.

Fill with peat moss or soil and it’s ready to use.

Repeat the process with the second half of the original tube and you’ll have two home made starter plugs!

Two plugs from one tube.

How much will you save?

About 20 cents per starter plug.

A package of 100 plugs from one of the major garden stores costs $21.31, which works out to a cost of just over $0.21 each. Three cubic feet of peat moss from the same store is $11.67, which works out to a cost of just about $0.009 per cubic inch. Each little cardboard box will hold just about 1 cubic inch of peat moss.

While you won’t get rich making your own starter plugs, the savings will add up over time, especially if you have a large garden.

Gardening season is nearly upon us, and with spring just around the corner, it will soon be time to start germinating the seeds for this year's crops.