Carol, "Also, I'm confused about the need for a base. Wouldn't having one actually inhibit the ground from acting as a heat sink?" The base just goes around the periphery, to give something solid to mount the greenhouse to. It doesn't cover the floor. There is apparently quite a bit of misunderstanding about the role of a "heat sink" or a "thermal mass". But the base is needed for mechanical stability, and isn't relevant to either a heat sink, or to a thermal mass. I am currently building an 8' x 16' lean-to kit (from Essex Greenhouse), and I am excavating down about two feet to bury several inches of foam insulation to prevent the ground from acting as a heat sink. I will install some crushed rock over the insulation to act as a thermal mass. I want the floor of my greenhouse to stay relatively warm during the winter. A heat sink is the thermal equivalent of an electrical short to ground or a ground wire. Just as you don't want to leave your windows open during the summer with your air conditioner running, or during the winter with your home heating running, you don't want to try to warm the planet during the winter with your greenhouse. The thermal mass acts as a battery or a capacitor that you charge during the day and discharge during the night, to help keep a more even temperature in the greenhouse and to make it more energy efficient and pleasant for you and your plants. I don't want to have cold feet while puttering in my lean-to during the winter, and I don't want my plants to have "cold feet" either. So I want to avoid a heat sink, and hopefully my insulation under the floor will do that. My floor material, and the black-painted concrete blocks supporting my benches, will serve as thermal mass. MM

Given the choice, I would go with all vinyl framed thermopane, especially as very few of them in a GH need to be operating and non-operable windows are not all that pricey. But as long as nobody lobs a fast ball into them, unlike polycarb, that will have to be replaced sooner than later and in the sunny south, sooner- glass will last as long as your home. To keep the costs down, check out what is available in your local home centers and determine which sized windows are stock and what sizes are the least costly, then frame the GH to accomdate them. Another benefit of glass is the ease of cleaning it and the ability to use the cheapest yet most effective means of totally removing the mildew, mold and algae inherient to all GH's; bleach, which is deadly to polycarb. Then, there is the shadecloth you won't need. Just go back to what was used on glass GH's before polycarb: water based whitewash. Spray it on in spring and power wash it off in fall. I do agree about making it larger than you think you will need. They are never as large as we think we need. Or, construct it with doors at each end, with the thought in mind of adding on later. And do use an insulated door. It would seem a pity to construct a GH like that, then lose heat/cool through a door. Or, go with a really heavy, tightly sealed insulated storm door, not the lightweight junk that comes with most prefab GH's, even the most expensive ones. However, for framing, think twice about using cedar. The average cedar now sold is not only far more expensive than treated, it's not what was available 40 years ago. All of the tight grained old growth is gone and what is now on the average priced market is soft, fast growth farmed lumber that will rot out faster than treated. Good quality treated lumber, if gone over with several heavy coats of any good oil based penetrating stain sealer, will outlast cedar by a mile, and look good for years. And- when you do restain it, if you dribble any onto the glass, you can use paint thinner that would destroy polycarb to wipe it off and/or go over it when it dries the same way you would any window; with a razor scraper. Then- talk about a garden GH as a class act...

One decision you should make before starting plants is whether you want to grow determinate (DT) or indeterminate (INDT) plants. Your planting system will depend on the choice you make since DTs will grow bushy and are usually either caged or supported with a weave. INDTs typically lend themselves to a stringline support from the greenhouse framework. Since DTs are usually earlier and produce a flush of harvest in a shorter time, they might be more suitable for that winter crop that you start now. On the other hand if you prefer a prolonged harvest into next April-May then INDTs might be a better choice. You probably shouldn't mix types. As with growing anything in a greenhouse you are best to start with as little disease as possible since plants are in closer environment and most diseases tend to spread rapidly. Therefore, I'd start plants from treated seeds in a sterilized planting media. Transplanting older plants from outside is risky. You might even want to remove and remaining plant residue and clean and sanitize exposed surfaces. A bacterial or viral disease could be disastrous. There are many planting options: in ground or pots, raised or level beds, close or moderate plant spacing, heavy suckering vs. no suckering. You might even be considering hydroponics in which case you should do a lot of reading and materials selection before jumping into growing this season. As Stressbaby mentioned Trust is a reliable INDT greenhouse variety. I've grown it for 6 years and only regretted the cost of seeds, >25 cents each. Most other varieties will perform well in a greenhouse, better than field grown. Temperature regulation is important but tomato plants are forgiving as long as you don't freeze (120F) them. The fruit may not be as attractive or plentiful in adverse temperature conditions. Enjoy your new venture.

Joanne, Remember, I warned you.......Nothing connected with greenhouses is ever simple.....The answers to these simple questions will get long and sometimes deep. When you do something and it turns out not to be the best of choices, don't get upset and want to change everything, just try to figure out a fix. That's really half the fun, right after you finish pulling your hair out!!!! Now, greenhouse on concrete slab..... Yes, the slab is or probably is level, and smooth. you can drill holes in it and anchor the greenhouse to embedded bolts, and it won't go anyplace. But. If you put the foundation flat on the concrete it will NOT drain. the wood will swell when it gets wet, and seal the greenhouse to the concrete, and little water will escape, keeping the wood wet and sealed to the concrete. Redwood won't rot, so there is not a huge issue with rotting your foundation, just the capture of water. If you raise the foundation off the concrete with spacers so water can drain, then you have outside air leaking into the house, interfering with your interior climate control, and costing you much $$$$$. The critters will find these spaces too...they have this uncanny sense for locating warm places in cold weather, and moist places in dry. Another issue is that concrete that is kept moist or wet is the perfect medium for algae growth. It will get green, and very slippery, not to mention smelly and unsightly. Every greenhouse I have ever seen with concrete walkways had them elevated a bit above the floor of the house so they would dry quickly. There always seemed to be at least one low wet spot that would require a Clorox wash periodically to prevent a slippery spot. If you put the house on level ground, the water will keep the soil inside moist, aiding in the humidification of the inside air. Perhaps a gravel cover to prevent soil becoming mud, and maybe a few rough textured "stepping stones" placed in strategic places would help. You could build a perimeter of brick or concrete blocks to put the house on, and pile dirt around the outside o them to fill the cracks, and aid in draining water coming off the outside of the house away from it. See how simple it all is? Yes, I did post some information in Greenhouses and Garden Structures on this forum. A lady there has posted an absolutely stunning blog with very detailed explanations and photos of the greenhouse she and her husband built. You can surely pick up some pointers there. I also gathered what few photos I had and posted a very brief story of my "very portable greenhouse". No culture or construction details there, just the story of one young sailor obsessed with doing something a bit different. Check my profile. Don't let me discourage you with my ramblings, just gather info and make the best decisions you can based on your specific conditions, and ENJOY. Bill