Some Gardening Info from My Other Blog

When I was in college classes for Horticulture there were some things that were immediately helpful to my gardening skills, two of those tools were understanding what is meant when a plant is given a growing 'zone' and how to understand light requirements.
So, to share a bit of the wealth, I have decided to break it down for those who don't already know.
Zones are based on average winter lows and the smaller the number, the more cold hardy the plant is. Example, a zone 3 plant can stand a very hard freezing winter, and a zone 8 plant is probably tropical. Zone 3 is somewhere in Canada most likely, and a zone 8 is in south Florida. Got it. Now some people even break them down further and say things like zone 5a or 5b, if it is a rather large zone. That tells you for sure if it is hardy to that zone or only marginal.
An example, of a marginal plant (one that can still die, even in the zones specified if not given proper protection in winter) would be some of the rhododendrons that are zoned for zone 5, but I use to live in central Illinois and we were considered a zone 5a, the colder half of zone 5. So if we had a particularly bad winter one year, or my rhododendron was in an unprotected spot, it may not survive even though I am technically a zone 5 and it should be hardy.

Purple Rhododendrons can be marginal

That is why in a previous post I talked about mostly only using plants with a cold hardiness zone of 4 or lower, because plenty of plants with a zone 5 were only marginal in my region of the zone. I had some very pretty roses one year, but they were hardy to zone 5, and when it came around to the following spring they had died back all the way to the root. Only the root survived the cold winter and so I ended up with a very vigorous red rose instead of the pink hybrid I had purchased... (hybrid roses are grafted onto the root stock of a more vigorous variety sometimes)
Roses are a bit temperamental in general, but there are plenty of other plants that do the same thing, but they are not grafted on a root stock and so you lose the whole thing. Lavender is one of those. I have tried and tried to keep different lavender plants that say they are hardy in a zone 5, but they always die in the winter, and if they do survive, they are so maimed why keep them.

Now on to light requirements. First off, full sun is not all day sun! That said, full sun equals 6 hrs or more of direct sunlight. Typically the more sun the better, but it is not required for the plant to live. 
For flowering plants, sometimes when they are not in full, all day sun they tend to not bloom as well, but they will live and be beautiful. 
Part sun therefore is between about 3-6 hrs of direct sunlight, and shade is 3 hrs of sun or less in a day.

There are also different types of shade. Dappled shade, as in a bed under a very tall tree, where light comes in through the leaves and where the branches are trimmed up very high from the base of the trunk (picture a very tall tree, and the nearest branch from the ground is 6-10 feet up). 

Big Leaf Hydrangea's like dappled light.

This is most common under deciduous trees (non-evergreen, lose their leaves in the winter). Dense shade is that of evergreens, or trees that have branches hanging very near the ground, or very heavy leafing trees, like maples and lindens. Not much will grow well in dense shade except moss and moss requires it to be damp dense shade.

Another shade condition is the north side of buildings, which are usually a problematic spot, because it never gets hardly any direct sun and a building does not create any dappled light. Yet, as long as it is open aired and there is nothing to block early morning and late evening sun, then there is still hope to grow some shade plants there, like ferns and Hosta and some shade loving shrubs like Japanese Kerria.  
So hopefully that sheds some light on some of these issues (the pun is totally intended). 
One thing that I will mention is that these light requirements do not carry over to indoor plants very well. If you are growing a cactus, obviuosly it needs high light indoors, but that is a totally different kind of light than the full sun mentioned above. It is unrealistic to expect it to receive 6 or more hours of direct sunlight in a day, but I shouldn't get started on that subject, I have not the time or energy to tackle that topic.
For another day, and until then, I hope this was helpful.