If you have an old, disused greenhouse on your property that you would like to start growing plants in again, here are a couple of changes you might want to make before you start doing this.
Get a glazier to fit panes of toughened glass in the greenhouse
If the greenhouse is quite old, then its panes are probably made from non-specialist glass, which can shatter very easily. If you're planning to use this structure again, it would be worth asking a glazier to take out these panes and put ones made from toughened glass in their place. As the term implies, this glass is made in a way that increases its durability and makes it better able to sustain forceful blows without breaking. This is important, as a greenhouse is normally used to grow plants that would be killed by the cold or eaten by pests if they were grown outdoors.
As such, it is vital that the glass of the greenhouse in which plants like this are grown won't shatter the moment it is struck by, for example, a football or a fallen tree branch, as during the few hours it might take a glazier to replace the glass, the plants inside the greenhouse might fall prey to the effects of the cold air or the appetites of nearby pests.
There is no point in buying this expensive, specialist glass, however, if you don't get it fitted by a glazier but instead decide to do it yourself. The reason for this is that if the glass does not fit perfectly onto the greenhouse's frame (i.e., if there are even a few tiny gaps between the panes' edges and the frame), cold air and tiny pests (such as aphids) will get into the greenhouse and put the plants inside it at risk of damage. Only a skilled glazier will be able to perform the fitting of the panes in a way that will ensure that there are no gaps of this kind when they're finished.
Consider relocating any big structures that surround the greenhouse
If you have installed several other structures around the greenhouse (such as your children's swing set, a tall garden statue or a large shed), then you should consider relocating these items elsewhere before you begin growing plants in the greenhouse.
The reason for this is as follows; greenhouses feature a lot of glass because this material allows sunlight to penetrate the walls of the structure and reach the plants inside of it. This, in turn, ensures that these plants receive enough light for photosynthesis to occur in their cells and for them to then grow as a result of this chemical process. If there are big structures surrounding your greenhouse that stop sunlight from reaching certain sections of its interior through the glass, then the plants in these areas will not grow. As such, if you don't remove these structures, you might have to avoid using the darker sections of the greenhouse.