Substitute for Park Bio Dome Plugs?

kathmom(NE WA)April 5, 2009

As opposed to last year when I went overboard in starting seeds, I am doing much less this year and (obviously) I am late to begin germination in my Park Bio Dome. I ordered refills on Mar. 18 and over 2 weeks later I see they are "shipping soon". I am afraid they may be backordered and haven't told me yet. Without getting the plugs, I probably can't use my Bio Domes, so I'm looking for surefire ideas to start my veggies and a few flowers. I have a heat mat and grow light; will start them in my basement and move to my (unheated) greenhouse when it warms up a little more--we still got snow 2 days ago here.

Thanks for any suggestions!!

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amna(6 (MA))

You could use Miracle gro seed starting mix (not potting mix) as a substitute for the pellets. Alternatively, I've ordered bulk peat pellets from Novosel ( they're pretty fast with shipping.

Good luck,

    Bookmark   April 5, 2009 at 8:22PM
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I have one of the Park Done, and I believe you are talking about the sponges? The holes are long, cone shaped that would not really lend itself to using potting soil as a substitute. I've been thinking about it myself as I have not liked the results I've gotten from my transplanted starts this year. The sponges seem to hold the roots in too well and the plants do not grow. I have some tomatoes I upplanted in February that are essentially in the same state they were when I transplanted them. I have another group I did three weeks behind the first where I tore off most of the sponge before repotting that are doing great, so I believe the conditions and feeding regime are adequate.

Next year, I will use the dome structure, but I won't use sponges. I am thinking of paper, rolled into a cone filled with potting mix. Perhaps you can try that and let me know how you like it. Newspaper would probable work, but it would take some time to roll that many cones and fill them.

All in all, the dome has been a terrible disappointment to me.

    Bookmark   April 6, 2009 at 4:11PM
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lgslgs(z6 SE ohio)

We always use seed starting mix (filling in the holes in the styrofoam insert with it) when we use the biodomes and it works great.

In fact, we've got 4 more biodomes on order (and yes, Park has them on backorder) and when they arrive we won't be using the sponges for seed starting. Maybe for rooting cuttings - or maybe you'll see me trying to trade them away on the garden exchange board. :)

We like the dome structure and the styrofoam inserts - but the sponges don't impress us a bit.


    Bookmark   April 6, 2009 at 6:15PM
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kathmom(NE WA)

Thanks for the advice. Park's said I should get my sponges in 7-14 days (if not, "be sure to call them back"), but I think I may try some seed starting mix, maybe with the newspaper. I appreciate the help!


    Bookmark   April 7, 2009 at 1:02AM
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lgslgs(z6 SE ohio)

Kathmom - we just got notice today that our biodomes shipped. Hope your sponges are back in stock and shipping soon too.


    Bookmark   April 7, 2009 at 10:31AM
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jollyrd(Richmond VA)

I tried the BD plugs 2 years ago. I did not do a very good job and the plants did not survive outdoor. But, two years later, I still find plugs, completely intact in the raised garden bed -- they claimed to be biodegradable. I do like the tray and dome structure so I might try the suggestions above on how to fill them with starter mix. I like the length of the holes.

    Bookmark   April 7, 2009 at 1:47PM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

Tested them several years back and ruled out using the sponges right away. The results from almost any seed starting mix is much better - both germination rates and later growth.

So just use your foam tray and dome, fill the cells with damp seed starting mix, poke a hole in the top of it, and plant. They will work fine that way.


    Bookmark   April 7, 2009 at 5:54PM
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kathmom(NE WA)

I did cancel my order of the plugs/sponges, no questions asked. Could have waited and got them, possibly, but wanted to get going. I rolled up newspaper, which wasn't too hard once I got the size right, and the seeds germinated more quickly in the Miracle Gro starting mix than last year in the sponges, I think. Problem was that I got some mold where the newspaper decomposed, so I sprayed with water/hydrogen peroxide and am moving seedlings out as soon as I can.
Think I will fill any more empty spots with just the dampened starting mix--the newspaper isn't working as well as I'd hoped. My only concern was getting seedlings out of the foam tray without something around the roots, but think this has got to be better than dealing with the creeping mold.

    Bookmark   May 7, 2009 at 12:26AM
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My wife, The green thumb, ordered this system too. Late getting here, order not complete, another 3 weeks for the sponges to be delivered. After she read this post, she was determined not to use the sponges and wanted to go with seed starter soil.The problem is in making a support system for the cones. She bought the 40 plug system. Fortunately,she is married to a Nurse that had a minor in microbiology and is also a certified mechanic.(just tooting the horn a little). I devised a means of easily making little cups that you can make and place in all 40 cones easily and quickly. You only need a souvenir baseball bat (Available at many ballparks or at Academy Sports, usually for less than $5, a saw, sandpaper, and some lightweight brown (unwaxed) paper (lighter weight than a grocery bag. About like parchment).
For the 40 count tray, cut the bat about 3/4 inch from the oval shaped Imprint in the middle of the bat (going towards the handle end) and sand the blunt end flat and smooth. Next, cut the brown paper into 5 inch squares and fold around the blunt end by placing the paper over the bat end and even up the edges , then fold the flaps as neatly as possible around the bat end (we slightly crease the two "wings" at the top and fold both in the same direction (either CW or CCW, Doesn't matter). Then, while the "cup" is still on the end of the bat, insert the whole thing into the cone and spread the cup by gently moving the bat around in a circle like a joystick and pull the bat out. Now the cup should be seated in the bottom, spread out and ready for seed starter soil. We cut off a small funnel to facilitate filling with the soil. If formed like I said, there should be just enough paper sticking up to facilitate removal of the cup for transplanting. We also put a hole in the bottom of the cup with a straight pin to facilitate fluid absorption through the bottom. I don't know the size of the 60 or 18 plug systems, but I presume this would work with them also, you would just have to move the cut on the bat either more towards one end or the other and you will need to figure out what dimensions your paper should be cut to.
BTW...if you take the part of the bat that was cut off and not used and grind or wittle it to a point, it makes a damn fine dibble for smaller seedlings or seeds.
As for those of you that have a fungus problem, remember, fungi are notoriously omnipresent in the air and any device used for seedlings should be sanitized in prep for planting to avoid or delay the onset of fungal problems (Just like brewing beer, my personal preference). A good spray down with a 1 to 10 mix of bleach and water followed by a good rinse in clean water should do the trick.
Hope this helps. I talked the wife into a trial run comparison of the sponges to the cups that we made and we will see if there is any rooting differences. We will post the results in a few weeks or so.

    Bookmark   February 2, 2012 at 11:45AM
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t-bird(Chicago 5/6)

excellent info pday!

I just had my first biodome experience, and it didn't go well - but definitely user error here, so I may try the extra sponges I have left over.

Sad to hear they are not breaking down.....I think their lit claims they are better than peat pots which don't break down completely....oh well.

I'll use up the sponges and see how it goes, then try some of these potting mix ideas. Are the sponges natural sponge? anyone know?

payday - any chance of a photo expose as you run the experiment? i'm having a hard time imaging this little bat making the pots.....

    Bookmark   February 14, 2012 at 12:08PM
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I have two of the 18 size blocks ( and sponges) that I got with my Bio Dome. Could the bottom 1/2-3/4" of the sponges be cut off of the sponge and be used as a "plug" and the rest of the hole be filled with "other" soil mix? What do you think? Would be used to start herbs and some peppers ( Habs and Scotch Bonnets etc.). Thanks Craig'S

    Bookmark   September 17, 2014 at 8:55PM
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I'm not sure what the reason is for retaining any part of the plug? Why not just use the potting mix entirely?

    Bookmark   September 28, 2014 at 6:29PM
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With the blocks being open ended (top and bottom), wouldn't the soil mix alone ( with out plugs) wash out of the block holes from watering? Wouldn't this happen either watering from the top or bottom. The "plugs" would NOT be used when transplanting the seedlings unless roots had entered the plug. I would think that a loose soil mix wouldn't hold up very well under watering and wash out.

    Bookmark   September 28, 2014 at 10:05PM
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The biodome and similar designs are intended to be bottom watered. But if you firm the potting medium into the cells - and that's a potting medium with a lot of peat or coir in it - it shouldn't "wash out" unless you are watering over-vigorously. If you are using a very gently top watering method it isn't going to wash anything out, just soak down gradually. Any more than that and you are over-watering.

There are older seeding methods (may still be used commercially or for specific plants) that involved seeding directly into large flats of fine vermiculite and then "pricking" the seedlings out and repotting as they emerged. I don't know if that is at all common any more but I've never cared for that method myself as the pricking out of the seedlings is to fiddly for me. Commercial growers used to do it (and still may) because it saved space and it saved pots, especially if you are working with a low-germination seed.

Anyway the point is we do not want to use a vermiculite seed starting mix in these types of containers, or anything else that is crumbly when damp.

Start with a moist potting mix. If it will hold its shape, more or less, when you squeeze it into a ball in your hand, that should do.

Tamp it firmly into the plugs (not Magilla-Gorilla firmly but just enough so it is going to hold together and there are no voids in the medium). Water from the top gently if you like, but bottom watering is actually usually easier. Either way, you don't want to leave it sitting in water all day. It should soak up into the medium fairly quickly, otherwise you've over watered. "Fairly quickly" being on the order of an hour or two.

Bio Domes ARE a bit larger than most plug systems. Its more like the ARS system I used years ago (which is still available). Its sort of a cross between actual plugs and regular plant paks. I had ARS system containers up to 4" individual cells and nothing ever washed out of that. Of course it is a bottom watering system as well.

    Bookmark   September 29, 2014 at 12:37PM
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I too used the BioDome and sponges last year and the sponges left a lot to be disired. Would it be wise to cut some cheesecloth or even gauze to line the holes and then fill in with potting mix? It seems that the whole idea behind the sponges is that the soil will never leach into the water below and the sponge ensures the seedlings get watered via absorption..

    Bookmark   February 7, 2015 at 8:47AM
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