Root Development Problem on Seedlings

I've got 30-some seedlings that should be in the ground right now, but I'm having a terrible time getting the roots to develop enough to put them out on their own. I have about a dozen white widow, about a dozen purple kush, and about another dozen G13-haze hybrid. I've grown all these strains before, many times, with no troubles at all, and I'm at a loss to figure out what I'm doing wrong this time.

What I typically do is germinate the seeds, then as soon as they start to pop, stick them 3/8 of an inch deep into a Grodan 3x3x3 growcube. I usually have roots coming out the bottom of the cubes within a week.

This year, however, the grow shop was out of cubes, so I bought some growslabs and cut them into cubes. There seems to be something different about the water absorption characteristics of the growslab rockwool as opposed to the precut cubes, because what's happening is that water is pooling at the bottom of my homemade cubes even after the top is totally dry. The moisture profile between the top and bottom of the cube is very different than the precut cubes that I'm used to using, very uneven.

What I suspect is happening is that so much moisture is collecting at the bottom of the cubes that the roots don't have any incentive to develop any further than the the bottom third of the cube. I've tried drying the bottoms by placing them on top of dry soil and other mediums, hoping it will "wick" the water out from below, but that's not working. The bottoms continue to remain moist, and the only way I've found that works to dry the bottoms is to hold back water so much that the tops dry out and the plants start to die. Which obviously defeats the purpose.

I'm not sure what to try next here. 3 weeks since the seedlings sprouted, and only 3 of the 35 plants have root growth coming out the bottoms of the cubes - and even those 3 only have 1 root each, about a half inch long. I tried using a rooting concentrate to promote root growth, but that was 5 days ago, and doesn't seem to have had any effect. I think my next step is to start cutting or pulling away the bottoms of the cubes until I get to the root structure. If i can't get the roots to come closer to the bottom of the cubes, I may have to just bring the bottom of the cubes closer to the roots. Anyone else have any ideas here?

Thanks in advance!

I just went through something similar with peat pots. My god, what a nightmare. Must have lost 2 months of growing time between two batches before I scrapped the pots. I guess some materials screw up the water displacement, aeration etc inside the containers and this can be devastating to tender roots. I can tell you're driving yourself nuts about it as I was. Check my grow journal, you'll see me trying to figure it out lmao. I solved the problem by putting some in mini smart pots and some in plastic containers. Never again with the peat pots, lol. Best Wishes.

Nice to hear you talk so much about roots! They are truly what determines a plants overall development and capacity to produce.

I too have a few seeds that are slow to root-web up this run, so what I have done is, placed the seed start insert tray right onto the heat mat, removing the wicking tray which the insert sits in, and covered it back with the humidity dome. I turned the heat mat down cause it's directly in touch with the insert tray, so now I'm using less heat to keep more of the entire insert tray at a better and more suitable temp for seed germination.

This helped me to keep an even moisture throughout the rockwool minis and root riot cubes I am using. 9 of the beans that had been in cubes for awhile sprouted once I made this change. Only 5 had sprouted before, and there are at least 15 still on the tray in cubes.

Hope this helps some.

Before you used it did you wash it and soak it in PH'ed water? The ph in some of those can be way out there. Good luck.