Has anyone used capillary mats for indoor seedling trays or small pots? Or nursery benchs or retail?
I'm thinking off putting watering mats into 11"x21" trays, because I can't seem to stop overwatering from above), and have not found a tidy way to bottom-water.
I'm new to seed starting indoors, I have a few trays in my bedroom, don't wnat to carry trays back and forth to the bathtub for bottom watering, and don't like removing water from trays with a turkey baster.
I assume that I can arrange a tray of inserts or plug cells so that it sits on a mat in a tray, then just add water once or twice a week to the tray without waterlogging the cells, inserts or pots.
How do you "prop up" things that sit on the mat so they have good contact, yet don't squeeze it flat?
Do you just sit the pots on top of the mat, which rests on water in a tray?
Are the grooves in the bottom of a tray sufficient support?
Or do you perch mat and pots up above the water level and wick water up to the mat from a bigger reservoir below?
I've seen 100 foot rolls of highly absorbent, reversible, light-weight non-woven polyester, for rapid wicking, that supposedly resists crushing. At $150 or $209, that's enough for 200 or 300 trays at around 70-75 cents per tray. I would only try that as part of a co-op buy.
I found a $16 24" x 94" 'Agrilan Fibertex' mat with a "permeable cover to reduce evaporation", designed for greenhouse bench watering. At $2 per 11x21 tray, I wonder if it has any benefits other than the much smaller minimum order. https://www.greenhousemegastore.com/category/s?keyword=capillary+mat
Then there are many very expensive "systems" like Burpee's "Ultimate growing System", $20 per tray, using a $4 mat. I might order one of those replacement mats to see what it's constructed of, if I ever order from Burpee again. I see similar but larger things online, around $10-15 per tray.
I'd appreciate any experiences people would care to share.
This message was edited Feb 3, 2011 11:24 AM
Capillary mats for seedling trays
Has anyone used capillary mats for indoor seedling trays or small pots? Or nursery benchs or retail?
I' ve been using capillary mats with the standard 1020 trays for a few years now. Just set my cell packs on top and keep them moist. I use a watering can and just use that to keep my mats moist. I was dismayed to learn that the source our master gardener's group used for buying the mats was no longer in business. Some alternative suggestions: use some inexpensive terrycloth towels. I actually think this would work really well.
I also found some fairly reasonably-priced capillary matting at:
I also use the Gardener's Supply APS seed starting systems, but usually go to the 1020 flats with cell packs as my seedlings grow. Capillary mats work great--I never top-water.
Hope this helps--feel free to ask if you have more questions. I'm sure more people will weigh in with additional suggestions.
I've purchased some of this, but haven't used it yet. It looks like it is durable and will wick well.
Thank you, that is very helpful.
But ... reasonable prices ... from LEE'S VALLEY! Amazing ... no, I think I'm wrong. they always have high quality items ... they just aren't CHEAP.
At $20 for the equivalent of 9+ trays - $2 / tray - that's not bad. It's the same square-foot price as "Agrilan Fibertex" mat with a "permeable cover to reduce evaporation".
When they say "Comes with a plastic underlay" - is that part of the material of the mat, or just some plastic film you can lay under it?
>> How do you "prop up" things that sit on the mat so they have good contact, yet don't squeeze it flat?
>> Just set my cell packs on top
Thank you! That sounds simple. I assume you mean "put the mat into the bottom of a tray, and the cell packs on top of the mat".
I am going to have to get some. And I like Lee's Valley as a company.
I've purchased several "wall paper trays" from Lowes in which I stand my seedling cups. I keep a thin layer of water (not more than a ¼" deep) in the trays at all times. The seedlings water themselves. I never water from the top unless for some reason the soil dries out, which it very rarely does using this method.
Hmm, I never heard of those. 22" long by what, 6" wide? I see a price of $3.16. It looks like thsat prevents tipping better than the 11'x21" low trays I use.
So you leave water in the tray at all times, and they still don't get water-logged? Pretty good! You just set pots flat on the tray bottom, with no mat or spacer?
I found it annoying to have to suck the excess water out of the trays with a turkey baster, but "just leave them sitting in it" sounds easier. Maybe the new mix I made this year will be aerated enough to allow that. I'll try!
Roman 22" Wallpaper Water Tray with Guide Item #: 245893 Model #: 202325
RickCorey_WA - I've had my wallpaper trays for several years. One is approximately 32" by 7" and the other size is 6½" by 15"
Yes, I leave a thin layer of water in the trays at all times, and no they don't get water-logged because I add lots of perlite to my soilless mix. I can't tell you the exact percentage of perlite, because I just "eyeball it"
Yes, I set the cups on the bottom of the trays without a mat or spacer. (What is a spacer?)
I stopped using peat in favor of coconut coir. When I raised African Violets I discovered that coir does not attract fungus gnats.
I like the depth of these trays, because as you said, it prevents the tipping of the pots better than a shallower tray - as long as you have the tray filled with pots that is.
I also save every conceivable tray/cup brought in from the supermarket. Clear containers with clear covers make dandy little greenhouses!
I purchase coconut coir from Worms Way they call it "classic coir"
It also comes in a 4.5kg block
The other type of coir they sell is too coarse for using in a soilless mix.
Thnaks for that link, I added it to my 'favorites'.
I like coir, too, but heard it can sometimes have too much salt in it. Do you flush yours before using it?
>> I add lots of perlite
I added some perlite this year, but I need to find a cheaper source.
I got a big bag of very coarse vermiculite, but that may leave the soil soggy even if it is aerated.
Last year I added sand and some coir, but I think the sand was too fine and the coir too coarse. Also, Tom Clothier disses sand for strating seeds, preferring "chick grit". If the only downside of sand is that it isn't sterile, I can live with that because neither is my pine bark.
I've started using lots finely shredded pine bark, just this year. So far, only for WS, but I plan to use it for indoor seed starting also.
When I set pots down on a tray, the holes may sit flat on plastic, and hence be mostly sealed shut. From what you're saying, I guess water still drains in and out, but I was concerned about the restrictions. Sometimes I lay down window screening under pots, to keep that opening open to air and water. I guess that's not needed!
RickCorey_WA - I use 3oz plastic Solo cups. At the very bottom (flat part) I poke one or two holes.
Around the perimeter where the flat part meets the wall, I poke several holes.
1/3rd up the side of the pot, I poke more holes around the perimeter.
The ones around the perimeter where the flat part meets the wall allows water to come and go.
The ones 1/3rd up the side allows air in and out. Roots like to breathe.
You are correct; without a "spacer" the holes in the very bottom are more or less sealed shut. Thanks for explaining what a "spacer" is :)
Even if/when I use regular "plant pots" I poke holes in them. My hubby sharpened a letter opener to a very fine point to use. I've also used a six-inch nail with a sharpened point, but it hurt the palm of my hand "poking" the holes!
If you need a photo of a pot to better explain - I'll try capturing the idea in one for you. I don't think you can see the holes very well in this photo.
I understand. Sometimes, with some pots, I would use a hacksaw and cut a little kerf into the "corner" or edge where the pot wall meets the bottom.
I only drill the higher "air holes" in 5 gallon pots, and have not grown anything in one of those for 15 or more years.
"Spacer" is just my word. there to be a better term! I've used bamboo skewers as "spacers", but they roll if you don't split them. I think even toothpiocks might be enough to break the seal. If plastic trays had more and smaller grooves, this might not be necessary.
But window screening works, and slightly reduces the tendency of small Dixie cups to tip over, by "bridging over" the ridges and tunnels in a tray.
I like the "kerf" idea.
When I lived in South Florida, there was a window re-screening company near-by where I could pick up free pieces. I don't know of a similar place here.
I found some rayon batting on sale, and used that in 10"x21" seed-starting trays indoors. Worked fine, absorbed a lot of water, seemed to transfer pot away from over-watered cells or pots and to quickly-drying ones. It had plenty of "loft". But it absorbed a lot of soil and matted down when dry, and was generally flimsy, so that I threw it away at the end of that seed-starting season.
Than I found some plain old cotton flannel that seems to work about as well, and was strong enoguh to make "wicks" that would carry water down and away from trays. It would probably also work to carry water down from a reservoir INTO trays.
Does anyone know what the most absorbant, most "wicking" cheap fabric would be? Cotton? Rayon? Some synthetic? Whatever they make synthetic mop-heads out of?
And what kind of "weave"?
woven fabric (thee must be many kinds of woven fabric)
The clerk at the fabric store seemed to have no idea. She thought Rayon would not be absorbant because it was "plastic". But she made this point: cotton must be "the most absorbant, becuase they make diapers of it".
Corey--what about terry cloth? Would just something like inexpensive hand towels work?
Flannel or felt would seem like a good choice, as well.
I thought about terry cloth (cotton, right?) but didn't see it in the fabric store I checked. I'll look for second hand towels from Goodwill. They should have ideal "loft" which seems desirable so they will press against the soil through holes in pots or cells, and reach down into the "gutters" of the trays.
The only felt I saw was made from recycled soda bottles, and that didn't sound very absorbant ... but I'm just guessing. "Felt" sounded reasonable to me.
I was also looking for fat, thick yarn made from something absorbant, but only saw wool and something like Orlonh, that didn't feel absorbant. There was flubbsy cotton "rope" that looked like it would unravel and was expensive, but I got a little. I'd rather roll up some flannel and maybe take a few stiches to keep it rolled.
Al (tapla) suggested buying a synthetic mophead and trimming those off.
Corey - you probably already knew this, but you can purchase capillary matting. I've never used it, as I prefer the method I outlined above.
>> you can purchase capillary matting.
Mostly, I'm cheap. Also, I like to "make my own" if I can.
Corey - as I said above, I've never used capillary matting, but from what I've gleaned from others, the matting can get clogged with algae. Peroxide should (might?) prevent this problem.
>> the matting can get clogged with algae. Peroxide should (might?) prevent this problem.
I don't know, but I would also expect peroxide to prevent algal growth.
Wouldn't it take an awful lot of algae to actually decrease wicking?
Once a fabric has filled up with enough algae to somehow clog the fibers, killing them might not regain your wicking..
Again - I just don't know. But all the more reason to find cheap, biodegradable wicking fabric!
Funny that neither rayon batting nor cotton flannel have turned green in my trays, even though my soil surface often does, when I've sprinkled vermiculite on top. Maybe the fact that I let the matting dry out between bottom waterings discourages the algae? Or maybe I'm diluting my Miracle Gro so much that not even algae thrives!
It gets dirty, yes. That's one reason I went from batting to flannel: I epxect to be able to clean flannel.
Corey, I'm sure that once you start experimenting with capillary matting, you'll find ways to make it work.
It's doing pretty well in trays. Either I'm learning to overwater less, or, more likely, it protects the roots against my over-watering.
I think the main variables are
"how cheap?" and
"does it disintegrate in one season?" and
"can I get it clean enough to re-use?".
Corey - I think the matting protects the roots from over-watering. As long as it stays wet, the soil/roots suck up the water.
I poke holes around the base of 3oz Solo cups and only add water up to those holes - which is very similar to using capillary matting.
I agree 100%. Pulling water away protects from over-watering, and assuring that ANY water in the tray reaches EVETY cell protects aginst overwatering, and differing needs of each plant.
Or at least it makes me feel that way, so I DO water less ofetn.
Well, I'm late to this thread of course, just stumbled over here while having my morning coffee, but I can say that I have used "real" capillary mat for years. Years and years, over and over! The initial investment has paid off many times over, in seedling health and ease of maintenance in the greenhouse. I covered whole benches (lined with plastic and slightly sloped) with mat, and flooded it on a regular schedule, and the plants wicked up the moisture at their individually required rates. They are designed to have a top (toward the plants) and a bottom side, to regulate the wicking. Crushing was not an issue. No over- or under-watering ever occurred. And if you put a timer on the water supply, it's completely automated. I could go away for weekends and not worry about a thing. That was the Good Old Days. When we moved I had to give up the greenhouse, but I still use capillary mats in 1020 trays. Algae can grow on anything, but I just wash the mats (with nothing but plain old water) every season. They don't rot, like textiles will do. And I never had disease problems either.
I bet this same info is available somewhere else on DG, but couldn't help saying it's worth it to get the Real Thing. I think I bought mine from Charley's Greenhouse Supply - back before there was internet search available.
Hmm! If they can be re-used for years, suddenly they sound like a much better deal.
They rayon batting turned to dirty mush in one season.
Cotton flannel in 1020 trays seems to decompose and tear after one year. I THINK that's because I let salts and acid build up in it.
After I sue up the first batch of cotton flannel that I bought, I think I will try ordering some "real" capilary matting. When I did a Google search, I found many vendors, but not every store that carrries it showed up in Google.
I've been starting my own seeds for 3 years and have had really good luck. I've just recently retired so I do get to spend a lot of time watching soil moisture, temp, etc., but the idea of a capillary mat has really caught my attention. I'm planning a week long vacation trip and was going to have a neighbor watch my seedlings, but well, you know... So anyway I ordered some matting that should get here before too long, but in the mean time I can't shake the feeling that the amount of seed starting mix pushing out of the bottom of the seed tray cells is enough to actually contact the mat and wick the moisture up. I'm using 72 cell plastic trays. Could I enjoy my vacation more if I put a small wick in the bottom of each cell and then have that come in contact with the main mat? While waiting for the mat to arrive, I did do a test using an old t-shirt and cutting the bottoms out of a 9-pack of peppers and it seemed to work, but I had to press down to hard from above to make sure there was good contact. I don't like treating my seedlings that way. Has anybody else used an "extra" wick in each cell, or have another idea?
Bismarck, eh? I'm not far from there! And used to live in central ND - Carrington area - which is where I had my greenhouse.
The only issue with your seedlings not getting enough water in the cell packs will be if the bottoms of the cells are indented, as can happen if you're re-using old cell packs and pushed up the bottoms to extract the plants, last time. Just be sure that the bottoms are all as far down as they're supposed to be - all level. It will work without any wick, I promise! It seemed like an amazing idea to me too, but by golly, it was great. You can also call the people you ordered from and ask. Can you mention the brand you bought? Maybe I can take a look and see if it is similar to what I had before.
Are you arranging to have the mat flooded regularly (water timer or some such) while you are gone?
If you want to experiment with capillary action effectiveness and possible-fail scenarios while you're waiting, take an old cell pack that has one or two indented cells, put some seed-starting mix in it, and set it on a wet washcloth. *Really* wet. I've never done this, but it ought to work - Rick was using various textiles to produce the same effect, but with the disadvantage of the "gross" factor - rot etc.
I used to work in a nursery where the grower for most stuff had the greenhouses on-site. He was forever watering from the top, and had to physically be there to do it. He grows really great stuff, but boy howdy does he have to work at it. I'm so tempted to set up my greenhouse again (probably a two-week construction process, given the site leveling and foundation prep that would be needed) and automate it with capillary mat etc, and have him come and see how he can reduce his aggravation and worry factors by a huge margin!
Thanks for the quick response! I see you are also in zone 3b. I'm right on the border of 3b-4a so I use 3b just to be a little safer.
The mat I ordered is from http://www.gardeners.com/Capillary-Matting/40-385,default,pd.html. It's 21 inches by 3 yards, so I'm thinking of cutting it along the 21 inch side which should give me enough to hang into the water. What I am doing is cutting 1.5 in Styrofoam pieces to fit inside the plastic tray and then placing 2 more strips below that to create a reservoir. I've attached a couple of pics of my test. The t-shirt has been staying wet but I don't think it is thick enough. Is the cap mat thick and does it get soggy? Actually FedEx tracking says it will be here today so I'll get to start right away. I don't try to save the 9 cell packs. When I transplant out to the garden the cells usually get ruined (I put them in the recycle bin) so all my seedlings are in new containers.
I did top watering my first year with mixed results so I started bottom watering last year. I learned along the way that you can also over-water from the bottom by letting the water sit too long, so this year I take the cell packs out and let them sit in another tray for about 10-15 minutes each then put them back. That works really well. But again I'm retired so I have the time.
I'm a little anxious about leaving my "kids" home by themselves for a week but hopefully the cap method will work. I'm also not excited about placing 72 wicks into 6 trays. I don't think I have that much time on my hands!
Ohhh! You're using the capillary mat to pull water UP from a big reservoir. I haven't done thatg, just set coltton flannel on the bottom of the tray, and made sure the 72-cells actually sat on their bottoms, not suspended by the rim resting on the tray's edge.
Then I just manually poured enoguh water into the tray tgo get the cotton soaking wet, but no VISIBLE standing water. That way, the channels in the bottom of the trayh held a small reservolir of water, but none of the soiless mix was actually below water level. That would hold 3-6 days worth of water, with cool not-very-dry indoor conditions and no fan.
I never had any trouble getting a good conenction between the flannel and the soiless mix in the cells. I made the cells bulge down before I filled them, they had big slits or rather melted slots, the flannel had somed "loft" and my soiless mix had pine bark fibers and a small amount of peat.
However, I had to cut the rims off propagation trays, or ujse very lows water-holding trays, or the prop trays would have been held up above the tray bottoms.
I've thought about shoving tiny wicks (like cotton twine) into cells, but never had to.
I'm with Rick, I just cut the mat to fit the trays, and soaked it but good, re-wetting as required so I didn't have to top-water; and of course, as I said, in the greenhouse, whole benches covered with cap mat were flooded on schedule by a battery-operated timer that opened the valve from the house's water supply. Maybe having a good-sized reservoir to handle extra requirements during a week away is a good idea. You'll have to let us know how this works out. It's been a week since you got your stuff - is it actually managing to pull water up that far, from a reservoir?
I checked out the link for your matting, and it looks/sounds like it's designed to wick water from a reservoir, which is cool. Three yards of 18" wide for $20 sounds like a pretty good deal, really. I wonder how far it can be expected to wick water? There's nothing I can see on the site about that. All very interesting - looking forward to details of your experience!
Joan, interestingly enough I was just about to post my results when I noticed your replies. It works great! The mat wasn't quite wide enough to cover the styrofoam and reach into the bottom tray so I had to cut lengths to cover the top, reach down past both pieces of styrofoam and then about an extra 1/2 inch or so to reach and fold over in the bottom of the tray. I did this on both ends. I used 1/2 staples to hold the mat in place on the ends. (Look at the pictures from my earlier post)
Since I'm going to leave the "kids" home alone for a week I decided to use a wick for the toms and peppers but I also have some cabbage and broccoli that I just sat on the mat. Both methods seem to be working beyond expectations. Next year when I start I probably won't use a wick, but I'll be here to monitor the seedlings. I also probably won't use a wick when I pot up the toms. When I cut the mat to fit the styrofoam I ended up with a strip about 1 inch wide so I cut that into 1/4 strips about 1 inch long and put them through the bottom of the cells. A lot of work...you bet, but for peace of mind while I'm gone it was worth it. I placed everything on the mat on May 3rd and there is still some water left in the bottom of the tray after 5 days. The moisture in the cells seems perfect! Just moist enough to know the plants aren't being soaked.
After I had cut and placed the wicks, I poured a small amount of water from the top (OMG!) to soak through the cells and the wick, and also flooded the mat to make sure the water from the tray had a good connection. The wicks stick out of the bottom of the cells about 1/2 inch. Then I took some un-moistened starting mix and lightly sprinkled on top of the cells. My thought was to try and keep the moisture from touching the stems. (good idea? not sure). Since its been about 2 weeks since my last feeding, I'm going to mix up a weak solution of fish fertilizer and put in all the trays.
Like Corey tried different materials, I also tried an old t-shirt but after I got the mat I realized the softness of the mat probably helps with the bottom contact. I also was a little afraid of any dye or chemicals that may be in other materials. But I think that is probably just me.
If you're reading this Corey, thanks for starting this discussion, and to you Joan and all the rest for their comments. In a couple of weeks I'll let you all know if this method is a hit or a miss.
>> In a couple of weeks I'll let you all know if this method is a hit or a miss.
Great! It sounds like you have a really good system going.
>> but after I got the mat I realized the softness of the mat probably helps with the bottom contact.
I agree. The mat "puffs up" and the soil mix droops down ... but they should touch in order to establish a capillary connection. I would not try to rely on a mat-to-plastic-cell conection followed by a plastic-cell-to-soil connection. Maybe go to the cosmetics isle and buy a bag of cotton balls? One of those might be enough for three or four cells
I keep looking for an absorbant yarn, but not found any. The closest would be cotton twine, maybe butchers twine.
>> Then I took some un-moistened starting mix and lightly sprinkled on top of the cells. My thought was to try and keep the moisture from touching the stems.
I think that's a good idea. Tom Clothier talks about doing that with sand or grit. I use coarse shreds of pine bark as a top-dressing to reduc e humidity. Mulch! When coarse and loose on top of the cell, bark chunks don't wick much, and they dry out quickly. But then I can 't tell whether the actual soil surface is moist or not.
This message was edited May 8, 2012 2:14 PM
Just got back from a short vacation and the mat/wick/reservoir system worked perfectly! The total time away was just under 8 days. I filled the trays and left Wed AM and got back the next Wed PM. The trays were empty but still moist and the mats were still moist. The moisture level of the cells seemed perfect. For a longer stretch of time I guess I could make the bottom supports smaller to make room for a bigger reserve of water. So for what its worth, if you need to be away for a few days, this worked for me! Now its on to potting up the toms.
Gee, Dan, I feel bad that I haven't been on DG for a whole 3 weeks! It's been a madly busy time here, but that's the best of life, isn't it, when you're busy with things that make you happy. Gardening and getting in closer touch with family and friends, for me, and not so much time on the computer.
I'm writing to say thanks for your efforts to update us all on your results. I knew it would work! Not so sure the individual wicks were necessary, but with no time to experiment before your trip, you couldn't take the chance, I know. I hope at some point you'll have the opportunity to try cell pack-to-cap mat with reservoir, and let us know how that goes. Sounds like something I could definitely employ when I put my greenhouse back together on its new site, if it is effective, as I won't have a powered water supply in this location.
My tomatoes in the garden - planted the week before Mother's Day - are 18-30" high (I bought one extra-large one, hoping for early production), and all have green tomatoes on them, so I'm pretty happy with the prospects. Hope you are too! Have you set them out yet?
Hi Joan, time does get away once you go from preparing for the garden to being IN the garden. I also don't spend much time at the keyboard. For the cap method I did try the pack-to-cap method on some cells and it did work and next year I probably won't use wicks at all. I also found the cap method (wick or no wick) to be useful for the last few days of hardening off when the plants sat outside for a few days. I only had to check the reservoir to make sure the mats stayed moist. Everything is growing quite well! Don't want to rush summer but I'm already looking forward to harvest!
Well here we go again! Getting anxious to get onions started. Last year I said I wasn't going to use wicks for the capilary method but I've changed my mind. Wicks worked so good last time, why not just do it again. I saved all my wicks when I potted everything up so it's just a metter of cleaning them along with the potting cells and place them in before I place the starting mix. I'm going to use the same method as in my posts from last year, but I think I'll make the pieces that go into the bottom of the tray a little smaller to allow for a larger resevour. Can't wait to get started.
I've used capillary mats on raised platforms for years. As others have said, I re-use them year after year. I started with the Burpee system. Then, finding the plastic parts flimsy and short-lived, I switched to grids raised on 1 1/2" rounds of PVC in Permanest trays, much sturdier, from IGC:
The PVC rounds are extra.
I use 10:1 water:peroxide for all watering (some people prefer 9:1. At high concentrations it becomes a weed-killer, so I always measure), and sprinkle cinnamon on top of all pots to prevent gnats. I can be away up to 2 weeks and come back and find everything perfect.
I have never found wicks to be necessary as long as I make sure the bottom of the cell is not indented and the soil mix is pushed all the way down. Occasionally a purchased plant needs it, but that's it. BTW, I use commercial mixes, usually MG because it is easily available.
Pics 1& 2 are this year in a city window, the house is closed for the winter. The black tray on the bottom shelf is from Gardener's Supply, is quite sturdy,and comes with a raised platform and mat. I also use these outside later on, pic 3.
I also use the Gardener's Supply AWS deep rooting system with the tray and the capillary mat. I love it for starting the seedlings and growing on, since the plants actually draw up the water as they need/want to.
Hadn't thought to put them outside for hardening off, thought. Thanks!
P.S. I wash mine at the end of the season with a mixture of 9:1 bleach, cheap mouthwash ($1 and a splash of Ajax Lemon Detergent, not Anti-bacterial). Rinse well and dry in the sun. Good to go for next season...
I'm thinking I'll make more of the wicking platforms with a piece of wood/styrofoam and use a piece of felt as a DIY capillary mat...That's what the original is made of -- felt, with a perforated piece of plastic fused to it. I can hot glue mine together. The plastic helps keep the roots from growing into the capilarry mat. It was cheaper to buy the AWS 15-cell trays separately than buy that whole domed unit. $7.95/per, and I can fit them into the trays I already have.
I only use the dome for germinating, then poof, back in storage. And, I've since learned to shove those trays into some big clear plastic baggies. Provides the same greenhouse effect as the domes, but, for FREE. Can't beat free!
>> shove those trays into some big clear plastic baggies
Because I happen to have some 18" wide Saran Wrap, I like to use that.
This is the tray I use outside. It's a little bigger than the standard 11x22, and I can fit lots of plants on it. It fits well in the mini-greenhouse I use for hardening off. It's also great later on for parking things I haven't gotten around to planting yet, especially since we're gone during the week.