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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.

128-Plug Seedling Trays

Seedling starter trays that ship to you, ready to use right out of the package. Our Seedling Starter Trays are pre-packed with a tested mix of coco coir, peat, and cellulose binder that fit directly into our raft boards and media beds. Widely used in the greenhouse and nursery trades, these trays are also ideal for starting cuttings.

  • Description
  • Resources

Description

128-Plug Seedling Trays

How 128-Plug Seedling Trays Work:

These seedling trays are designed to germinate a wide variety of greens such as lettuces, kales, chards, mustard, collards, and herbs. Their compact size fits perfectly in the raft boards, Aquavertica towers, and all media beds. The plugs are made with a combination of coco coir, peat, and a cellulose binder that ensures the plug stays together around the roots through the point of harvest. Seedlings grown in these plugs have a high germination rate, good growth rates, and don’t require any pH adjustment. They are also compostable making them environmentally friendly. 6mm dibble on top of each plug makes seeding a quick, easy process.

Use these to start seeds and then transfer them to bigger areas. Plant your seeds as you normally would with soil and water in each plug. Widely used in the greenhouse and nursery trades, these trays are also ideal for starting cuttings. Each plug has a drain hole in the bottom.

The size of these plugs makes them the ideal companion plugs for our raft boards.

Product Details:
  • 128 Cell Plug Trays
  • Each Cell Measures 1.19 in. Top Diameter, 2.0 Inches Deep
  • Each Cell holds 1.53 Cu. In. or .85 oz.
  • Tray Can Be Used Alone, Reusable for Years
  • Made in the USA
  • Drainage holes in the bottom allow for top or bottom watering systems

Resources are being developed from this product. Please contact us for more information.

Seedling starter trays that ship to you, ready to use right out of the package. Our Seedling Starter Trays are pre-packed with a tested mix of coco coir, peat, and cellulose binder that fit directly into our raft boards and media beds. Widely used in the greenhouse and nursery trades, these tra …