Hi brandond, I am going to make some assumptions and hopefully give you some ideas to work and play with. Others may have different ideas and I invite them to pitch in. I do not have any experience with rain barrels but with irrigation in general. First, you probably will need to have a minimum of a two foot corridor in between your two 2.5 foot by 12 feet beds. That means 70 square feet of bed. Watering will be a trial and error because seedlings take a different amount of water than grown plants. It will also will make a difference how well you can control the climate inside the greenhouse. The types of plants you grow will dictate the type of actual water delivery system. The 55-gal. drums can be linked to fill and empty as one unit. Allow where overflow from the drums will go. You will have a system that will deliver water by gravity with very low pressure. There is approx. 0.5 psi for every foot elevation difference between water level in the barrels and the outlet in the greenhouse. So the delivery system will be very different than if you could pressurize you system. A low-pressure system needs larger diameter pipes or hoses to deliver water to an automated emitter system. Second, the amount of water you will need for fully mature plants is approximately 40 gallons per week. That is putting 1" of water on your two beds per week. That is 5 weeks of water for four barrels. You can automate your system with a battery-powered programmable controller attached to your hose outlet. If there is no rain within 5 weeks you will need to supplement the barrels from your house water supply. Also time how long it takes to fill a 5-gal. bucket from your greenhouse outlet. You can then calculate the time it will take to water your plants. As you get further along, let us know how we can help you with a more detailed low-pressure inexpensive delivery system. Aloha

Thanks for the info. We were told we had to fill them up then submerse them in water for two weeks and they would seal themselves. The problem is... Where? I got out there and played with them a little today. We had already drilled the holes in the top so I stuck the hose in one and let it go. In the beginning there were some pretty serious looking leaks but within a few minutes they were nothing but little sprays and they cleared up quickly. I guess between the pressure of the water and the wood swelling from the inside, the cracks sealed. I don't know. I have to check the water level tomorrow. Until then, hopefully the nice soaking they are getting from the rain will help a little. Thanks again for taking the time to reply. -Tina

Actually, the more I think about it, it definitely is a siphoning effect. The water level always drops to around 1/3 when this happens, and I have 3 rain barrels all connected together. Too much of a coincidence for it to ALWAYS drop to 1/3, with me having 3 rain barrels. I have my overflow pipe coming up from the bottom of the middle barrel in the configuration, with a hose connected at the bottom and running into the yard. Ideally, as the water level rises, it hits the upper level of that pipe (inside the barrel) and starts draining out the overflow right down the center of the barrel and into the yard. HOWEVER, my center barrel also happens to be a closed system. Other than the overflow pipe, there is no outlet to exchange air for the water coming into the barrel (the outside barrels both are vented - one with downspout entry, the other with a nail-sized hole on the top). So, when that middle barrel completely fills up (like it does in a downpour), it then completely fills up the overflow pipe and siphoning effect occurs. It then siphons ALL the water out of the outside 2 barrels, until enough water is siphoned out so that the level drops to the top of the overflow pipe in the middle barrel. It then slowly levels out the water from that 1 full barrel to all 3 barrels. That's why it's always roughly 1/3 full after this phenomenon occurs. To fix this, I need to get some air exchange happening in that middle barrel. To do so, I have to eliminate the "closed system" aspect of my middle barrel. I can do that by simply putting a nail-sized hole in the top like I did in the other. I think I'll try that first. Oh, and the reason I didn't see this happen when I tested this before, is that I didn't let the water completely fill high enough and long enough for the siphoning effect to start. It would have been a period of time AFTER the barrels all appeared full. I obviously didn't wait long enough. I think that makes sense to me. Make sense to anybody else?

Abnorm- I just checked Craigs List again. I found barrel saddles, a wheel barrel and steel drums but no barrels. Can you send me a link to the ad you saw? I'm just not seeing it.