Seedlings and Rockwool

by Tim
(MB, SC)

Would this work if I germinated the seed in a paper towel, then placed it in rockwool, then (last) take the little rockwool plug and put it in a cup and placed clay pellets around it? Or would I need to rinse the rockwool off the plant?

Answer: Tim- whenever you start seeds using the wet paper towel method, you want to make sure you transfer the seedlings to their new growing medium as soon as they sprout (and before the tap root gets longer than about 1/2 an inch long). There is only so much energy available to the seedling inside the seed itself, and it takes an incredible amount of energy for the little seed to put down a tap root. If the seedlings are not placed into the new growing medium in a timely manner and given a little seed-starting fertilizer, your success rate will be horrible.

Using rockwool as the growing medium for the new seedling has its own issue. Rockwool is notorious for having an alkaline pH. This can cause problems in all kinds of plants....full grown, and especially little seedlings. I recommend Rapid Rooter plugs, but if you are set on tying out the rockwool just be sure to pre-soak it for several hours in pH adjusted water first- or make sure you purchase a rockwool product that HAS been pH adjusted. Otherwise, your success rates (again) will be horrible.

Finally, once a seedling has grown roots through a growing medium, you want to disturb those roots as little as possible. If your seedlings were grown in a rockwool plug, you should not attempt to remove any portion of the rockwool. Simply transplant the whole thing into the next container and, as you indicated, support the seedling by filling in the container around the seedling with pre-soaked clay pellets.

It is important to pre-soak clay pellets,for a minimum of 20 minutes, because they absorb water slowly (and than drain rather quickly). Using clay pellets that are not moist enough may prevent roots from growing down into the clay pellets, even with regular irrigation cycles after that point.

If you are using the loose kind of rockwool, than your transplant will be much the same as transplanting a seedling grown in soil. You may want to loosen the root zone gently before transplanting, to promote the spreading out of the roots. If some of the loose rockwool falls away from the root ball in the process that is OK, but do not try to pick around the roots removing additional rockwool- simply transplant the seedling into the new container and treat it the same as if you had used a rockwool plug. I hope this helps you out Tim, and Happy Growing!

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Mar 22, 2010
Rockwool is inert...
by: Kev

This is the bit that I don't understand - Rockwool is inert and by definition should not need hours of pre-soaking as it cannot absorb anything - that's it's job; it doesn't react or interact with anything - all it does it hold the sproutling/seedling/plant in place. Although the pH-adjusted water is utterly correct and nigh-on essential. It should be enough to simply ensure the rockwool gets a thorough soaking so that the combined rockwool/water is pH-stable (there's a lot of alkaline rockwool dust inside virgin rockwool). Or am I missing something?

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