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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.

A Simple Guide to Starting Seeds for Hydroponics

So you’re ready to get started in hydroponics and you’re about to start some seeds…

But you have no idea where to get started?​

You’re not alone — when I first started gardening, I was a soil gardener.

Starting seeds for hydroponics systems was unknown to me until I started to build deep water culture and ebb and flow systems. Once I built those, I had to learn how to start seeds hydroponically.

One of the main benefits of hydroponics is the absolute control you have over your growing environment. Knowing that, I didn’t want to germinate seeds in soil and then transplant into a my hydroponic system, adding a bunch of dirt to the system.

There had to be another way.

Here are just a few reasons why you want to start seeds in a hydroponic system as opposed to soil:

  • Much cleaner than starting seeds in soil
  • Seedlings grow faster after germination
  • Easy to transplant into a larger hydroponic system

That second reason is a cool one. As soon as your tap root pops out, a hydroponic system is going to help it grow faster than soil and prevent it from becoming rootbound.

Step 1: Get Your Materials

You don’t need much to get started. If you build your cloner yourself, the rest of the materials will cost you under $50 bucks and will last you for quite a while. If you decide to go with a store-bought cloner, it’ll bump up the cost a bit but you’ll also be getting a much higher quality product.

Seed Starting Materials List

  1. Hydroponic Cloner – You can either build your own or use something like the Clone King and starter plugs (#3 below)
  2. 2″ Net Pots
  3. Rapid Rooter Starter Plugs
  4. Seeds – find at your local nursery if possible, or buy many places online. A personal favorite of mine is RareSeeds.com
  5. Air Pump
  6. Air Stone
  7. Tubing

Step 2: Fill The Cloner With Water

Fairly simple step here. All you need to do is fill up your reservoir to just under where your net pots sit. Don’t worry about pHing your water or using reverse osmosis right now – standard tap water will be fine.

Step 3: Set Up the Air Pump

Place the air stone in the reservoir and connect the tubing. Connect the other side to the air pump and plug it in. You should see some beautiful bubbles start to come out of the air stone. These bubbles are what will keep the roots of your seeds moist and stimulate growth.

Step 4: Place Starter Plugs and Seeds

Soak each starter plug in some water and then place it in a net pot. The moisture will help the seeds germinate.

Drop 2-3 seeds in each starter plug. We use more than 1 seed because not all seeds will germinate and we want to make sure that every starter plug has a sprouted seed – otherwise we’ll have to replant!

Step 5: Maintenance

This system is very easy to maintain as your seeds sprout.

If you want, you can place a transparent cover over the top to keep in some moisture and increase the temperature of the system, but it’s not necessary.

Make sure to moisten the starter plugs with a few sprays from a spray bottle every day so your seeds have enough moisture to sprout.

When your seeds sprout, clip off all but the strongest seedling from each starter plug.

That’s it! Your seeds should sprout in 3-5 days for most plants and you’ll be ready to start growing some truly epic plants in your hydroponic system in no time!

Video Guide

If you’re more of a visual learner, I have a three part video series from my YouTube channel​ that goes into the entire setup in detail.

Part One: The Basic Setup

This is the visual version of the blog post. Helpful if you just need to SEE to learn (like me).​

Part Two: Making Sure Seeds Germinate

This part of the series talks about some of the maintenance and troubleshooting you might run into when starting seeds, including the infamous “why do they keep falling over” problem that a lot of beginners run into.​

Part Three: pH Water and Add Nutrients

This part of the series talks about the need to pH and add nutrients to your reservoir after the seeds have germinated. Because they feed off of their seed leaves at the start of their life, you can get away with not doing this until the seeds germinate.

By the way, I’m using the Bluelab pH Pen​ to fill all of my pH needs. It’s awesome!

Starting seeds for hydroponics doesn't have to be difficult. In fact, it's really easy! Learn how to do it in 10 minutes with this Epic Gardening tutorial!