Easy Seed Germination with Polyurethane Foam

Most hydroponic gardeners germinate their seeds using either a solid media such as perlite, vermiculite or coconut fibers or a woven media such as rock-wool. The first germination alternative has the problem of making transplant stress higher, while the second has the problem of being too expensive (for most hobby and commercial growers). With that in mind, I intend to explain on this post how to germinate your seeds using a cheap cube of polyurethane foam which is readily wet by the nutrient solution and generates almost no transplant stress when moving the plants.
The first step to germinate seeds in polyurethane foam is to buy a sheet of the adequate polyurethane. For this purpose, I use a polyurethane foam with a density of 0.015 grams per cubic centimeter. The next step is to cut the polyurethane foam in 1 inch by 1 inch by 1 inch cubes. After this is done, you have to make a cut with a sharp knife at one face of the foam cube (this is where the seed will be inserted).

Once your cube is cut and ready, you have to presoak it in water. Simply squeeze the cube under water and let it absorb all the liquid it can. Once you take it outside, do not squeeze it again since this will make the cube exchange the water it just absorbed for air.

Now simply deposit each seed inside a cube and place the cube in a tray for seed germination someplace where the appropriate conditions for the germination of your seeds are present. You can keep the seeds and the surface of the foam wet by misting water over the cubes everyday. Once the seeds germinate you can place them in your favorite hydroponic setup and the roots will grow out of the foam cube, into any solid media or nutrient solution. (below, an image of my germination setup ready for seed placing).



  • hydroponic
    January 20, 2010 @ 6:44 am

    Thanks for the post, we will post your Hydroponic setups article. I will post for our customers to see your articles on your blog Hydroponic setups

  • case
    May 20, 2010 @ 8:08 pm

    where do you find this foam?

  • case
    May 20, 2010 @ 8:09 pm

    and what other plugs can you use for lettuce?

  • Amila
    July 23, 2013 @ 8:32 pm

    thanks for information. If you can use some pictures or drownings that illabarate how to use cuts in sponge will be helpful

  • Mark
    September 2, 2015 @ 8:08 pm

    Thank you for this information. I’ve been trying to see what alternatives there are for growcubes as I’ve heard that rockwool has similar effects as asbestos. Using polyurethane foam seems like a very good alternative. Peace.

  • September 28, 2015 @ 4:22 pm

    Thank you for sharing. How does effect density of polyurethane to plant ?

  • April 19, 2018 @ 12:41 pm

    I am a hobbyist, and have had good success growing plants in open cell polyurethane foam. Lately, I have become concerned if any toxic substances from the foam, could be released and absorbed by the plant. Do you know if this is possible?

  • September 26, 2018 @ 10:12 am

    This week I received 2 oncidium twinkles with their roots in and through foam cubes. I placed one in a bark/ sphag moss media and the other in a hydro environ. I am an experimenter at heart, but I find the grey foam in the hydro rather unsightly. I’m sure I could safely carve away some of the foam, but does anyone have a better suggestion? Of course, the safety of these little orchids is my primary concern. FYI, leaves and roots appear quite healthy in foam blocks.

  • January 26, 2020 @ 7:15 am

    Who invented the sponge type hydroponics system?

  • muhammad aamir khan
    February 9, 2021 @ 9:21 am

    I am a student of plant sciences who usually uses peat moss, coco peat, etc for germination. but I got some plugs which are made up of an unknown foam type. and the germination process is quite rapid and successful in these plugs. can anyone please tell me what is can be the composition of such type of growth media

    • admin
      February 9, 2021 @ 11:45 am

      These are probably rockwool plugs. These are made by spinning molten basaltic rock into fine fibers.

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