Orientation depends on where you are and what is convenient. In very cold places maximising solar exposure is key, so normally the long side is perpendicular to the sun. In hot places it isn't such a big issue, and people generally just pick an orientation that suits the location. It is probably best to put the door on the leeward side from the wind so your greenhouse doesn't pop windows. If you aren't getting light through a wall it is best to insulate it. The best insulated glazing is worse than the worst panel insulation. (1cm of foam is better than almost any glazing on the market) Heat retention is a product of insulation (R-value) times thermal mass. High insulation means you need less mass, high mass means you need less insulation. In electrical terms, the behaviour of a greenhouse is exactly the same as an RC circuit (R = insulation, C = thermal mass). You can work out the time in seconds for the temperature to drop to 40% of the difference (from say 90F to 60F when outside is 40F) by multiplying the R-value in K/W by the thermal mass in J/K. In imperial units use degF hour /btu for R-value and btu/degF for thermal mass and get the time constant in hours.

My grapefruit seeds appear to be doing well. They've grown little roots and they're pushing themselves up and out of the soil. One looks like it already has a bit of a stem structure. Anyone got an idea of how warm these should be. Our days range from 70-90 degrees. I know they grow well in states like Florida so I'm assuming this temperature range is okay. I also have questions on tomato plants. I put several seeds in a dish (not hoping for much) and they've grown very well. However, I planted them all in a very tight group. Obviously there's no hope of separating them without killing them. Do I cut the stems of the ones I don't want or will they work it out via survival of the fittest? Thanks again.

If you live somewhere with freaky weather it is always best to sow a few seeds and then sow some two weeks to one month later to act as back up plants should the first batch not survive. Its all about timing. If they stay in their pots too long, some plants just never do as well in the garden as those that got outside and in the ground at the perfect time. You'll never be able to forecast that "perfect" time so just take the risks you're comfortable with. Hot weather lovers like morning glories and zinnias do not do any better starting them early. They just kinda sit still until things warm up so there isn't a huge advantage to starting them early. They will set seed which will over winter and sprout next year but the zinnia seedlings won't show up until summer is half over and the morning glories will show up where you don't want them and also a bit late. Two things will slow down seedlings - lack of sunlight (much stronger than indoor lighting) and lack of warmth. It is better the keep them starved for light while you wait for things to warm up outside. Cool temps bring with them all sorts of rot problems with seedlings. If you're starting large seeds of things like melons or cucumbers just stick two or three seeds in each space and then use scissors to chop off the heads of the weakest plants after they're a week or so old. No need to risk damaging roots by digging them up to thin them. The headless ones will sink back into the soil over time. The truth about roots - the roots you see when you dig up a plant are not the parts of the roots that do the actual work of drawing in water and nutrients from the soil. The real workers as far as roots go are microscopic. Only superman can see them with the naked eye (and he ain't much of a gardener!). You can gauge a plants health by looking at its roots but the damage that is done by handling baby plants is to the microscopic roots. Some plants just freak out when those roots are damaged.

It depends on the severity of the rot. If it is small and can be repaired, replacements are probably your best choice. If the rot is more severe, a full tear out is the "only" way to go. As for the window choices, Andersen has a number of lines. Which one are you looking at?