At Gecko Grow, we don’t like carrying one of everything. We like to put some effort into curating a collection of products that do what they’re supposed to do – and do it well. There are many options to choose from in the world of propagation plugs, but what works best?
While calling something “best” can be highly subjective, we decided to get a little scientific and do a side by side comparison of some popular options. We wanted to see which plugs gave us the best results and which ones didn’t cut it. While we expected some variation in the results, we didn’t expect the huge difference we saw across the plugs we tested.
As a result of our testing, we have started selling the winner in our online store, and stopped selling a popular option because it ranked second from last! You may be surprised by the results we got. But first, let’s provide some background on why this even matters. Feeling impatient and just want the answer? Click here.
What is a propagation plug?
Propagation plugs are known by various names: peat plugs, rockwool, growing cubes, growing sponges, and many more. Typically crafted from materials like rock wool, foam, peat, or specialized spongy substrates.
The primary function of a plug is to provide a nurturing environment for germinating seeds, young seedlings, or cuttings during the initial phases of plant growth and to encourage the development of a healthy root system. Can you just cut up a pool noodle and use that? Sure, but you’ll get better results with a good plug.
To do its job, a propagation plug needs to offer 3 essential things to your young plants. First, they need to provide a stable support structure without restricting root development, ensuring that delicate seedlings remain securely anchored as they take root. Second, these plugs must retain moisture, creating an environment where plants can access a consistent supply of water without becoming waterlogged. Third, they need to promote aeration, allowing for the exchange of oxygen and carbon dioxide, vital for healthy root development.
There are, however, MANY options to choose from, and they all claim to be the best. But which propagation plug is best? What are the key characteristics you should look for in a propagation plug? How do you know which propagation plug will live up to its manufacturer’s claims?
Why Use Propagation Plugs?
Do you have to use propagation plugs? No. But there are definitely cases when you should and there aren’t any cases (at least none I can think of) where you shouldn’t. As long as you are using the right plug, you will see multiple benefits that will increase your chances for success. Some of the key advantages of using propagation plugs in hydroponics include:
- Optimal Root Development. A good propagation plug supports plants and cuttings during their early growth stages. While growing media like expanded clay or perlite is good for mature plants, it isn’t great for promoting germination and early root development.
Using a propagation plug ensures that your young seeds and seedlings have a perfectly tailored environment to meet their needs. The right combination of support, moisture and aeration will promote strong root development in the early days of growth and give your plants the foundation they need to stay healthy and happy. - Space Efficiency. If you don’t have a lot of space, for your seedlings, starting your plants in propagation plugs can be a huge game changer. Most plugs are sized to fit in a 10 inch by 20 inch 72 cell tray. This means you can have 72 plants growing in a very compact space. If you were to start that many seedlings in pots, or a typical hydroponic system that is spaced for mature plants, you would need quite a lot of extra room for your seedlings.
Our Hydroponic Gardening Bins offer a great example of how space saving using propagation plugs can be. If you want to harvest 4 heads of lettuce a week, and your lettuce takes 5 weeks from seed to grow, you would need to have 3 bins dedicated to growing lettuce. If you were to start your lettuce in a seeding tray using propagation plugs, however, you could grow all your lettuce in just one bin because lettuce really only needs to be in a larger system for its final 2-3 weeks of growth. - Simple Transplanting. If you are starting your plants with the intention of moving them to another location once they get bigger (either into your hydroponic system or even outdoors), propagation plugs are a game changer. Using plugs allows you to easily move your seedlings without mess (more on that later) and with minimal disturbance to the roots.
- Cleanliness. Loose growing media has its place and we love it too, but because it’s loose, it can get messy. Filling a seedling tray with loose media like Coco Coir or our Hydroponic Mix is a job best done with a tarp down. Filling a tray with propagation plugs on the other hand, can be done inside with little to no clean-up required (at least the good ones).
The importance of cleanliness doesn’t stop there. If your hydroponic system has pumps, sprayers, or filters, sediment from loose growing media can cause failures that can quickly lead to blockages, equipment failures, floods, and dead plants. It can also lead to a build-up of sediment in your system that can harbour damaging bacteria and pests if it isn’t cleaned regularly. - Easy to Use. A good propagation plug should make your life easier. While some need to be be pre-soaked, pH balanced, drained, and don’t come with a seed hole, others are ready to go out of the bag – just add water and a seed or cutting to the pre-drilled hole and the plug does the rest.
How Did We Find Our Favourite Propagation Plug?
To find the holy grail of propagation plugs, we wanted to test an assortment of plug varieties and brands under the same conditions. We definitely didn’t test all brands or all types, but we feel we got a good sampling with the 10 plugs we tested. We then set out 10 assessment criteria to test our plugs against. While no plug got a perfect score, the winner got 94/100, so we were pretty happy with that!
Here’s the assessment criteria we used:
- Ease of Separation. Some plugs come as individual loose plugs, and others come in a sheet that is connected at the top for easy handling. When the time comes for your new baby plants to be separated and transplanted, plugs in sheets need to come apart easily, or you run the risk of damaging your young plants (and making a mess).
- Cleanliness. A key benefit of using plugs is that they’re less messy than filling pots with loose soil, so we wanted to make sure the plug we choose delivered on this point and didn’t leave a mess to clean up after use.
- Water Absorption. Seeds need water to germinate, and seedlings need water to live. Whether bottom watering (like we did in our comparison), or top watering, plugs should quickly and easily absorb water without getting waterlogged.
- Ease of Seeding. When planting seeds into plugs, you don’t want to have to struggle to get a seed in. Some come with pre-drilled seed holes, while others don’t and you have to make your own.
- Ease of Cloning. When trying to grow a plant from a cutting (aka cloning), propagation plugs can be great, but only if they allow you to get the cutting in without causing damage to the plant, or falling apart.
- Sustainability. What happens to your plug once you’re done with it? We looked into the composition of each plug we tested to see which ones were made of the most environmentally friendly materials and would break down over time.
- Affordability. One of the benefits of growing your own food is saving money on your grocery bill. But if your plugs are too pricey, they’ll start to erode your savings.
- Plug Stability. Plugs that fall apart not only leave a mess, but can also leave sediment in a hydroponic system that can quickly lead to problems with pumps and filters and can harbour bacteria.
- Germination Success. If a plug does it’s job right, seeds should germinate. We planted lettuce seeds from the same seed package into each type of plug to see which had the highest germination rates.
- Clone Root Development. Similar to seed germination, we wanted to see which plugs did the best job promoting root development on cuttings. We took cuttings of similar size from the same tomato plant to see which plugs got the most roots.
The Contenders
While we didn’t attempt to try every plug available, we selected 10 options as a representative sampling of the different types readily available. We tested two types of rockwool, 100% peat discs, coco coir discs, four types of peat blend plugs (a plug type gaining in popularity), a floral foam, and a new plug type made of 100% hemp fiber.
To keep the comparison fair (and at a manageable scale). We loaded all the plugs into the same 10 x 20 propagation tray and staggered 6 of each plug around the tray. The exception being the 100% peat and 100% coco coir discs that only got one spot each.
The Results
Ease of Separation
The plugs that came pre-separated got full marks here. Of the ones that came in a connected sheet, the floral foam was the only one to not lose any points. It separated very easily and cleanly with just a little pressure applied between the plugs. Rockwool was slightly more difficult to separate and the hemp fiber was like pulling apart a piece of felt – it was do-able, but definitely didn’t result in nice, uniform plugs.
Cleanliness
The peat plugs all got full marks here. Most peat plugs are held together by a small amount of polymer binder that keeps them from shedding while handling, keeping your work area nice and clean. Rockwool came in second with only a small amount of fibers coming loose and was joined by the peat and coco coir discs which have a plastic or paper netting to keep everything contained. The floral foam came third with quite a bit of debris coming off while separating and handling. The hemp fiber came last as it left quite a mess of loose fibers after separating and handling.
Water Absorption
After all the plugs were placed in the 10 x 20 tray, we bottom watered to see what plugs would absorb water through capillary action. Most of the peat plugs as well as the coco coir disc had no problem here. One peat plug took a while to fully absorb, but in the end they all did it without getting waterlogged.
The rockwool took a few hours, but eventually became sufficiently saturated. After a few hours, the floral foam was still dry on the top, so we took it out and soaked it in a container of water. To be fair, it is recommended to presoak rockwool and to top water floral foam at the beginning, but this is an extra step, so they still lost marks on this one. The peat disc was scored the same, not because it didn’t absorb the water well, but because it absorbed too much water and got waterlogged.
In last place once again was the hemp fiber. Not only did it show zero capillary action in the tray, it also resisted absorbing water when submerged in water. After some effort, we managed to get the plugs wet, but it definitely took much more effort than expected.
Ease of Seeding
To get full marks here, the plugs needed to come either pre-loaded into a tray, or in a connected sheet that could be easily placed in a standard 1020 tray; and have a pre-drilled seed hole to easily drop seeds into (either manually or with a seeder). One peat plug, one rockwool and the floral foam met these criteria. The others (with just one exception) lost a point because they need to be manually loaded into a tray, but once that was done, were fairly easily seeded.
The exception was the hemp plugs. While they did come in a connected sheet, they did not have pre-drilled seed holes and getting a seed down into the plug was comparatively quite difficult.
Ease of Cloning
When cloning, you want to be able to get the cutting into the plug without causing damage and have the plug hang onto and support the cutting once it’s in. With the exception of one type of rockwool that was a little hard, and the hemp plug that really put up a fight, the plugs accepted and supported cuttings very well. The coco coir and peat discs were not part of this assessment.
Sustainability
For us and most gardeners, sustainability and environmental responsibility matter, so we wanted to make sure we took this into account when deciding on a plug. This category is where hemp fiber shines. It is made from the waste fibers of the hemp industry, is made in Canada, so it doesn’t travel far and is 100% home compostable. It was for this reason that we wanted the hemp plugs to win (yes, we did have some bias going into this), but sadly, this was the only criteria where they beat out the competition.
Peat can be a controversial product and the peat plugs contain a small amount of polymer binder, so they all lost some points there. They are, however, certified compostable, so everything is made to break down and be easy on the environment after harvest, and the peat is typically blended with other beneficial products like bio char or composted bark, so we weren’t too hard on them. The peat discs, however, come with a very nature unfriendly plastic netting, so the discs ranked a bit lower.
The coco coir discs scored well too. Instead of a plastic netting, they were wrapped in paper, making them 100% compostable. Coco coir is also made of a byproduct of the coconut industry, so using them makes use of a waste product. They were only edged out by hemp in this category because they are typically produced in Asia, so they need to travel quite a bit to get here.
Rockwool and floral foam took the bottom spots for sustainability. Rockwool is made from a natural product (rocks), but it is non-renewable, non-compostable, and takes a lot of energy to create (literally involves melting the rock and then spinning it like cotton candy). Floral foam is a 100% synthetic non-compostable product.
Affordability
It may not come as a surprise, that the least sustainable products happen to be the most affordable. Floral foam and peat discs had the lowest unit cost when we did our comparison, and rockwool was a close second. That said, two of the peat plugs had a comparable unit cost to rockwool, so still comparatively a good deal. Hemp fiber and coco coir discs came 3rd in affordability and the other two peat plugs came out most expensive.
Plug Stability
We also looked at plug stability. If transplanting into soil, this is less of a concern, but when using plugs in hydroponics, you don’t want plugs that will come apart in your system leaving sediment to clog filters, pumps and a mess that needs to be cleaned up. At the end of our 2 week trial, we checked the stability of each plug to see if it was still holding together, or if we would start to have issues with them coming apart in our system.
Only one peat plug got top marks here. All the others came apart when pinched or rubbed. One peat plug and both the peat and coco coir discs were no more stable than loose soil after two weeks.
Germination Success
While all the above criteria are great to consider (at least we think so), none of it matters if plants won’t grow in the plugs. While we are happy to report that seeds did germinate in all of the plugs, there was quite a range in how long it took for seeds to germinate across the plug types and how big the plants got by the end of our two week comparison.
The peat plugs germinated the fastest with all but one type germinating after the first few days. The floral foam also showed good germination success. The one remaining peat plug and the peat and coco coir discs took longer to show successful germination, perhaps because they absorbed too much water as they were more waterlogged than the others.
Rockwool performed fine, just not as well as the best peat plugs, and once again, the hemp fiber came in last with low germination success and much more time needed than the others under the same conditions. At the end of the two week comparison, the hemp plug had not developed any true leaves and the top performing peat plug already had 4 fully emerged true leaves.
Clone Root Development
The results on root development with the cuttings was very similar to the seed germination results with the peat plugs and floral foam showing the most root development, the hemp plugs coming in last, and rockwool doing slightly better than the hemp, but still not great compared to the winners.
And the winner is…
After we tallied up the scores across all 10 criteria, the winner was clear. The ihort Q Plug outperformed in nearly every category with an impressive 94/100 overall score. It outperformed the other peat plugs (the best performing category) and the next best plug type was the floral foam with a score of just 76 (largely due to low marks in sustainability, water absorption and cleanliness).
Rockwool, despite its popularity scored only 72 overall signaling that while it may have been a good option years ago, there are definitely better options available now and as a result of this comparison, we no longer carry rockwool in our online store.
Want to give the winning propagation plug a try? Click here to order from our shop.
Happy Growing!
