I am not an expert, but I have grown from seed successfully, and I do not like bottom watering. It can leave standing water, make the mix too wet and is difficult to measure, and leach nutrients from the mix. I personally much prefer careful measured overhead watering, into my pourous mix.

While it is good to have the bottom moist to attract the roots to the bottom, this isn't really necessary to overly worry about in a small pot, the roots will fill it out no matter what you do IMHO.

I'm sure others will disagree. There probably isn't really a right or wrong way. People have had plenty of success both ways.

I drench and drain. To make this worry free, you need a good draining medium. I think you need to match your watering habits with specific media since the specific medium dictates a lot about watering.

Effective bottom watering has a bit of a learning curve and takes practice but it is the most healthy method for young seedlings as it encourages deeper root develoment and less surface soil issues.

Just as with top watering, it requires a good quality seed starting mix. Quality mixes contain a wetting agent that encourages the mix to only absorb so much water and to absorb it uniformly so you in fact have more control, not less. It is self-regulating to a degree but without that quality mix one can over-water doing it either way.

And the type of container used also makes a big difference as the standard cell packs and related nursery containers are constructed just for the purpose of bottom watering. Homemade containers are not as effective with it. So if using standard cell packs and 1020 trays it is easy to do by either tray weight and/or time. Otherwise it is more a matter of guess work and finger sticking.

Either works when done properly and therein lies the problem. Most don't. they try to do it on some sort of artificial schedule and all plants at the same time rather than learning to recognize the signs different plants give you when it needs water.

"Or maybe I'm doing this wrong and when watering from the bottom you're not supposed to keep it watered until the top is noticeably wet? In that case it seems difficult to gauge how much water to use because the cells intake unevelny and they are also opaque which makes it hard to see how wet the medium is."

"Noticeably wet"? No. Lightly moist, yes. All you have to do to determine that is touch it. Hands on, not just eyeballs. :-)

Dave

Lots of how to bottom water discussions from over on the Growing from Seed forum

Wow Dave you have weighed seed trays to determine dryness? That's pretty cool, I would have never thought of that.

I have just gone with the "hands on" approach for determining watering needs myself. In my house though, I have extremely hot and dry heat and I need to be careful not to let the soil dry out. Last year I lost a few seedlings being too careful not to overwater. If the soil completely dries out it can kill just about anything, and it can happen quickly in my house, especially in a cell pack. It is definitely not an ideal seed starting evironment as it is too warm but it is what I have got. So it is not just the plants and the soil but your growing environment as well.

I agree with grubby and Dave, well, except Dave's part about "Noticeably wet". You do have to notice the soil darkening to know the drench is done so drain and drip-dry.

tj

I use a combination of overhead and bottom watering. When overhead watering seedlings, I use only a mist bottle with a pump. The medium is moistened before loading into the trays, it sits overnight, checked for even moisture, then gently loaded into the cell trays and sown. After seeding, a light misting is done repeatedly until the soil is less-than saturated. Water is put into the bottom tray, a dome is placed over top, and away they go. The dome is taken off for a while, and put back on throughout the germination time depending on humidity of the air and the moistness of the mix. Some seeds are given heat. If the soil shows too much drying, it is misted. May seem like a lot of maintenance, but it's really not.

You do have to be careful with domes, it's just experience which lets you know when to remove it, and when to keep it on. I like the the surface slightly moist, but not overly wet. Too dry, and crusts form. Too wet, and damping off can happen.

Bottom watering, with a good medium, is just science. Capillary action and cohesion are the active forces. Water... wicks. The key, as was mentioned above, is a good seed starting medium. If you are having trouble bottom watering, more than likely you are working with a medium that lacks the structure favoring the bottom-watering technique.

Btw... especially in times when I did not have the money, nor enough pots, I transplant my plugs into paper Chinese food containers. Being square, they fit very well together into a tight mass on a tray. However, being wax coated, as long as you don't puncture them, they are water tight. If you rub off the wax they disintegrate. The only way to really tell if they need watering is to pick them up and weight them in your hand. That too, as was mentioned above, is just experience. Again, too much water...because they don't have drainage holes, the soil compacts and you lose air pockets. Too little water, well, that's obvious.

"Dave you have weighed seed trays to determine dryness? "

You don't really have to weigh as in "on a scale" although you could if you wish. It's just a matter of lifting a drying out tray and getting a feel for it vs the feel of one well watered.

Sometime when your cells/tray are filled with your moist potting mix but before you plant the seeds, lift it and see how it feels weight-wise. Then it is just a matter of lifting each tray once a day to feel how the weight changes as the soil dries. After 50+ years I could probably do it blindfolded and can do 30-40 trays in just a few minutes. But it doesn't take much practice to get a feel for it if you are "hands-on".

The problem arises when folks insist on mixing a bunch of different plants with different water needs in the same tray - never a good idea - or have a tray with several different sized containers in it.

Our cell packs never leave their trays. Water is poured into the trays, let them sit for about 15 minutes, finger tap the soil surface of a few of the cells and if moist, dump out whatever is left in the tray. But that all depends on the type of equipment you are using.

Dave

Thank you everyone. For those that spoke of ideal mediums, can you tell me which ones you use or even better a recipe?

I was looking up recipes online and they all seem to be different but somewhat similar revolving around differing ratios of peat, perlite, vermiculite and maybe compost.

The one I'm using right now is 8 parts sifted compost, 4 parts peat, and 1 part each of perlite and vermiculite. I've sterilized in a grill at 180-190 for at least 30 minutes

I would prefer to construct my own since I have vermiculite, peat, etc. available and I am trying to save on costs.

Thanks

This is my third year starting my own plants from seed. I bottom water and have had good results. I use Farfard seed germinating mix i get from a local greenhouse supply company. When mix gets dry I ad enough water to cover entire bottom of try and it absorbs up into mix. I know I have over watered before and it has not caused any problem - just the mix looks extra wet on top for a few days.

Unfortunately I have no choice but to mix plants in the same tray... I have a small space to start all my plants. So given that yes that is another reason for me why I shouldn't bottom water. I guess it would make a lot more sense doing it watering an entire tray like that.

I don't have watering problems with seedlings. I take them outdoors whenever possible.

I top water and can tell mostly by the weight when they need watering...usually every day when they are outside.

I do a combination of watering methods, depending on the plant and what stage it's in.
Right now, I'm using some 1x1 cells for sprouting early nightshades and herbs. I start out with mostly bottom watering, but at some point in the seedlings growth, I start watering from above like what would happen out in the garden every 2-3rd watering. Kind of do with water currents what one does with wind by setting up a fan. I do also like to run a fan to stimulate the wee things too.
If I'm planting in 3x3 pots, I tend to start out with the bottom water soak, but top watering in general. Usually what gets planted in those are repots or sturdier faster sprouts like squash or beans.

And it is a weight thing. Pots feel different when well watered or not. I always lift my flats to "test" them to see if they need watering or not.
Now, this can get a bit more complicated if I'm mixing plants in trays. Then I tend to stop bottom watering so much and top water each plant type according to how it looks and what it's weight feels like. For instance, basil sucks the water right up, but thyme and oregano are slower. So I water my basil more often.

camper... I use what's available in my small town. Last year, and I still have some left over that I hope wets well because of the peat (I'll soak it, then dry and loosen. I may have to add a drop of dish soap,) was Jiffy Natural & Organic Seed Starting Mix. It's peat, coir, and vermiculite - balanced with lime. It's really all that's available at the box hardware stores (Home Depot, Lowes) as there aren't any good nurseries for an hour's drive. It seems to be a fairly good product, I've had no trouble.

I think there was one from Miracle Gro that was pre-fertilized, but since I start in 72 cell plug trays, there's little need for fertilizer. I used to mix my own seed starter, but the pH is always off some from the peat, and the little I need is a small expense.

I don't like compost or soil in my seed starting mix. I'm not saying it's bad or good, it just adds food for fungi, isn't always consistent, and besides... seeds are self-contained, needing little to no fertilizer for enough time as it takes for the plugs to be transferred into the transplant containers.

If I could have liked Daves post twice, I would have. Yes, and yes, use commercial mix for your seeds. Good commercial mix.