Carrots don't germinate well in hot weather. And they bolt, too. Maybe August isn't the right time to grow them. But next time, try soaking them indoors in more moderate temperatures before planting. I have read that you can plant them with a squirt bottle rather than trying to get the tiny seeds out of the water. I intend to try that next time I plant carrots.

I have never built a self-watering bed, but it seems like it should work.

I have seen plans for them online. I don't think you want to poke holes in your pond liner. It is your reservoir. You want it to hold water. You need to provide a way for water to wick up from the reservoir to the soil medium. The wick has to reach down into the bottom of the reservoir.

The reservoir might be filled with gravel. You can keep the soil out of the gravel by using some kind of cloth or geotextile. The cloth would have to have holes where the wick goes down into the reservoir. The purpose of the reservoir is to hold as much water as possible. Therefore, use uniform sized gravel. Do not put vermiculite in the reservoir (you can put it in the soil if you want). Ideally, you wouldn't put anything in the reservoir but water. But then how would you support your soil? So, the gravel is a compromise.

Make sure you give yourself a way to fill the reservoir, and you will also need to avoid over-filling it. You could leave some kind of fill hole/overflow hole just above the pond liner level, or in the top of the pond liner.

You should study how the earthbox is constructed if you are not already familiar with it. In the earthbox, the wick is basically a tube which reaches down into the reservoir. The tube is filled with the same potting soil as the rest of the box. Small holes at the bottom of the tube allow water in. The potting soil composition ensures good wicking action. A little bit of soil escapes through the holes in the tube into the reservoir, but that doesn't seem to cause any problems.

You could use something similar, but you will need more than one wicking tube because your bed is much bigger than an earthbox.

If you do it, please follow-up with details. I would love to hear how you make out.

--McKenzie

Thank you, McKenzie, good food for thought.

The carrots germinated in the constantly wetted pot at the same time as I was trying to get them going in one of the raised beds. I think they would need at least twice daily watering to keep from drying out, but that's really when I need to plant for a fall crop.

When I was saying I would put some holes in the pond liner, I did mean as an overflow up near the soil surface, so there would be 12-18" of reservoir to hold water below. I was planning to have the soil/vermiculte do the wicking rather than have a separate reservoir compartment below the soil, but I will have to think on that subject a bit. It seems like the soil would end up washing down into the gravel eventually anyway since this isn't something I can really take apart and reassemble, like a normal SWC. I think what I'm really trying to do is restrict drainage enough that I can maintain a somewhat water-logged bottom layer that will keep the top layer from drying completely. Luckily, I have all winter to think on this, and room to make three beds, so I could try different approaches to see what works. If nothing else, it should be interesting!

Lantana, sounds like a LOT of work for some carrots!
Usually I sprinkle mine within some greens so they get some shade, or else I give them a sprinkle, then give them a good watering each day and cover them...with a sheet, cardboard, shadecloth, something to help keep them cool and damp to germinate. Nancy

Oh, I had them covered to keep them moist, too. These would be intensive beds closest to the back door for herbs and fresh greens. Being able to grow carrots would be a bonus. They would be easier to cover with shade cloth or plastic as needed to extend the season for our salads. It will be work to dig out the sod and put another bed in there anyway; may as well make it something that really adds to the garden's output and reduces my work when I'm really busy in mid-summer. It will also mean that I don't have herbs in pots on the deck demanding daily watering in the summer.

Most of us trying to create a condition that the soil has a GOOD DRAINAGE. But you are trying to do the opposite.

I dont remember off the top of my head very many garden vegetables that prefers wet feet. Most will get root rot in that condition.

You can experiment and find out if it works.

Yeah, I am pretty sure you need a reservoir separate from the soil. With an air gap between them. Otherwise it will be a soupy mess at the bottom.

Geotextile cloth can keep the soil from settling in to the gravel. Roots will probably penetrate it, but it should last for years anyway.

So the stackup can be pond liner, then graded large-size gravel, then geotextile, then a thin layer of pea gravel, then whatever potting mix or soil you want to use. Overflow must be below soil level.

As noted, you need wicks to let the moisture seep up from the reservoir into the soil.

I think it is an interesting idea and if you want you should go for it. But if you just want to grow carrots, try soaking the seeds first to see if that solves the germination problem.

When you noted that the seeds in the container germinated, I thought the container was inside your house where it is probably cooler. I guess that was a wrong assumption on my part. So I think you are right that it is the constant moisture that was the important difference.

--McKenzie

Thanks, the geotextile is a good idea, I will look into that. You're right that soil in the bottom would probably create anaerobic conditions, which might create some problems later. We have weird soil here - yesterday I was cutting sod, and it was really damp in most areas, then I would suddenly come across a spot that was bone-dry for no reason. Add to that the materials like saw dust that haven't completely broken down in my raised beds, and it's just not a great germination environment for smaller-seeded plants. I had success with beets and radishes in the same bed, but only manage brassicas and lettuces in spring when it's cool. When I make these beds they will be filled with vermiculite and store-bought potting mix most likely. I think it will be much better for succession planting of things like lettuces that like their moisture. As it is, it's just too much work to get them going after about May, and I use lots of straw mulch around bigger plants, so tucking them into shady spots doesn't work out too well either.

Thanks again for the input. I will be sure to take photos and post as this project progresses. Yesterday I got all the sod cleared from the area, but now it's supposed to snow on Saturday, so I'm not sure how far I'll get before winter hits for real.

I like the idea. When farm land became scarce the Myans would build a log raft and dredge soil from the swamps, placing that soil on top of the logs. Basically building a floating bed. I have seen several modern set ups that grow greens on a floating mat.
That being said I would look at placing inexpensive 4" black drain tile in the bottom to reduce the need for gravel and allow for more water holding capacity. If you know any builders you may be able to get this for free.
You'll need to get an effient way for the water to wick into your soil above, you could use a heavy natural fiber rope drilled into the drain tile extending into the soil, in several locations. If you know any sailors you may be able to get this for free.
I agree with the post above, you will need a break from your soil to your reservoir otherwise you will have wet feet and a muddy mess. I would recommend a piece of rigid foam insulation. This should not only prevent over saturation or your boundary layer but may allow your ability to extend the season -assuming you could put some type of greenhouse over the entire bed.
Either way, I think your onto something cool. Another thing you could try that has worked for us; drill a hole in the bottom of a 5 gallon pail, install a fitting that will allow you to hook up a soaker hose and loop the hose around your rows just below the soil line. Just keep the bucket filled -and keep a lid on it.

I have two 4'x8' self watering beds. They truly are self watering because they are filled every time it rains by the overflow from my rain barrels. The reservoir under each bed holds about 150 gallons. Even during the hot dry summer of 2012, I didn't water these beds except to get the plants established.

You do need a reservoir below the root zone and wicks to bring the water up. I used columns of soil inside perforated drain pipes. The overflow should be located at the top of the reservoir but below the root zone. That will prevent the roots from sitting in water.

I even grew carrots in one of the beds last summer; they did great. But don't expect the top few inches of soil to be wet enough to germinate carrots. In my experience the top inch or two stays very dry. The water just doesn't wick all the way to the top. I am OK with that because it keep the weeds down.

I germinated carrots by laying row cover directly on the soil over the newly planted seeds and watered it 3 or 4 times a day for a week or so. After they germinated, I removed the row cover and let them get their water from below.

pawneepapa, what holds up your soil? Did you put gravel in the reservoir?

--McKenzie

My reservoir is actually 35-gallon barrels on their sides and plumbed together at the bungs. I cut holes in the sides (now the top) of the barrels and inserted the drain pipe. When I filled in the bed, the soil went down into the drain pipes to act as wicks. The reservoir fills from one end and overflows into the next bed, which I built about 4 inches lower than the first bed. As previously mentioned, these beds are plumbed into the overflow on my rain barrels. I initially filled them from the hose but I have never needed to add more water in the last 4 years. That includes the awful drought we had here in Kansas in 2012.

Plants in these beds typically do better than my other beds. I think it is because they have all the water they want but their roots are not continually sitting in water. Plus the rainwater doesn't have chlorine, which I think makes a difference.

While this system works great, if I were to build another bed I think I would dig the hole, line it with a pond liner, install short drain pipes vertically for the wicks, fill it with gravel (the bigger gravel size the better to increase the water volume), and use a landscape cloth, with holes for the wicks, to keep the soil out. It is just a simpler design plus I have had a trouble with tree roots invading these beds. A pond liner might keep them at bay.

Here is what these beds look like filled with soil and growing. The pipe sticking up above the soil is how I check the water level and where I would add water if I ever needed to.

pawneepapa

Thanks for sharing, really like this setup. Couple of questions, are the black pipes going into your reservoirs perforated or solid? And did you have to cap the bottoms?

Very impressive pawnee! Good job!

Wow. I think this is everything I could have ever possibly want to know answered right here in this thread. Thanks pawneepapa!

dajsnipe

The pipe is perforated and I cut the bottom to match the curve of the barrel. There was a small gap but not enough to let much soil into the reservoir.

Thanks

Wow, great information, and those are some great looking beds. Thank you so much for posting!