Bottom watering only is the standard recommendation. There are no benefits and several potential problems with top watering.

Dave

I tried bottom watering and wasn't very successful. I added enough water to my flat so that I literally had to weigh down my 3.5" durapots (which have four holes [the size of a hole punch] in the bottom of each) with wrenches from my tool chest.

After four hours of waiting it didn't seem like ANY water worked it's way up to the surface. Just prior to this I had transplanted my broccoli and dahlia seedlings using fresh sterile soil into the durapots.

So after 4 hours I ended up just using a spray bottle and soaked the surface periodically until it appeared to me that I had watered the transplants enough.

Did I just not wait long enough? Or do I need to modfiy the durapots in any way?

What was in these durapots that floated? What filled with? Dry mix?

The only time I have ever seen one float is if it was filled with dry mix that had never been properly wetted.

All potting mixes should be well wetted before filling a container. Most dry mix will not wick water.

And misting the top of soil only gets the surface, not the root level so the roots are force up to the surface to get water.

Dave

I used dry mix. Rookie mistake I guess.

But I only did this because I had no issue with my cell packs when I first started my seeds three weeks ago. At that time I filled a flat with my cell packs (eight 6-packs) each with dry mix. I then added water to the bottom of the flat and two hours later the cell packs were soaked from top to bottom. After removing the cell packs, draining the water from the flat, I placed the cell packs back into the flat and proceeding with seeding.

I just figured that transplanting into larger containers would give me the same results.

This leaves me with the following questions:

1) Why does dry mix not absorb water very well?

2) Why did it work for my cell packs and not my durapots? I bet it had to do with the height the water had to travel up.

3) How to properly wet (and not over-wet) potting soil for transplanting?

4) What do I do now that I transplanted already? Seems like the surface soil was still moist this morning and the air in my cellar is bone dry this time of year. This tells me that the moisture on the surface did not evaporate nor did it seep through the surface to drier soil beneath. Maybe I'll be okay in that case ???

It doesn't actually work with cell packs either. They may eventually soak up some just because they are shallow but it isn't a uniform wetting and dry pockets are left in the container.

Most all potting mix instructions will say something to the effect of "always wet the mixture before filling containers". Never have understood why some would do it any other way. Logic says to me why would you plant something in dry dirt? But for some reason folks do it so I've lost track of how many times this has been discussed here much less on most every other seed planting website.

Why? Same as with any other dry material - you first have to break the surface tension before it can absorb water. Depending on the material sometimes it just takes a soaking, other times some sort of surfactant has to be used but even a dry sponge won't absorb water until it gets wet.

How do you do it properly? Soak it in a bucket or large container using warm water, wring it out by lightly fist squeezing it, and fill the containers - whatever they may be - lightly finger compress in place.

Since you didn't, all you can do now is really well-soak them from above. It will take time and several doses of poured, not misted, water. (The only role for misting in growing from seed is BEFORE germination and then only if absolutely necessary. Otherwise it only encourages disease issues.) Do it until the water freely runs through. Then let them drain well, finger press to wring it out some, add more already we soil to bring the container level back up.

Doing it this way will wash any and all nutrients out of the container - replace them. You need to pour slowly, wait a bit, slowly pour more, etc. to avoid root damage. It will also water-log the roots for some time so no more watering until the soil knuckle deep is dry and then only bottom watering.

Dave

Dave, I had no idea it could be that involved to do it right. I guess I'll soak my next batch in a bucket like you suggested.

Interesting...the directions on my soil mix indicate to top water after seeding, rather than soaking the mix. However given my experience with top watering, I think I'll follow the advice given.

Sorry for the fuzzy pics:

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Not familiar with that brand. Is that what you are using for seed starting mix or also for the growing mix in the durapots?

So what happened then when you followed their directions? Did it quickly get wet once the containers were filled or did the mix just float up on the water and sit there?

Dave

It's the same brand I used last year for both the cell packs and eventually when I transplanted them into the 16 oz solo cups. Since those cups were much deeper than the durapots I have this year, top watering didn't seem to be an issue last year. But yes, in the durapots it (at least initially) was a problem. The water would float on top for a minute or two before soaking through. I only did the transplants into the durapots two days ago so I'm going to see later on tonight how dry they look.

Before I filled the cell packs for the tomatoes I'll be starting tonight I filled my 5 gallon bucket with an entire bag of potting mix, stuck it in my utility tub and starting filling it with warm water (not all at once). I used my arm to mix in a good amount of water until it it felt pretty damp. I mixed it really well reaching all of the dry mix at the bottom of bucket. It wasn't sopping muddy wet, just wet enough that I really had to wash my hand afterwards. After subsequently filling my cell packs (2 flats worth) with the wet soil I then let them soak in two inches of water in their respective flats for about two hours. After that I dumped the water from the flats and placed them on my heating mats to get the soil up to around 75F for a couple of hours so that when I sow them later tonight, the conditions should be optimal.

That is sounding like to much water in your mix. If it was already wet enough that it was really sticking to your hand, then why soak bottom soak it?

You want the mix to still be a bit crumbly. Wet enough that it will hold its shape when you squeeze a handful, but dry enough that it will crumble apart if you thunk it.

I use a potting mix with a wetting agent in it...Pro-Mix. Even then, I knead water into it till just moist. Not the whole bag at once, just the amount I'm using that day. After filling the pots/paks, and planting seeds, I bottom water in a tray for about 2 minutes.That's all it takes when pre-wetting the soil. Too much longer and your soil is waterlogged.

I'm not that concerned about it being water logged because my cellar is has bone dry air and the mix will dry out in a matter of a day or two anyway.

But yes I agree, next time I shouldn't bottom water once I've wet it with the use of the bucket.