Growing Common Marjoram or Wild Oregano

On a recent visit to Richters Nursery at Goodwood, I purchased some "Common Marjoram"/Wild Oregano seeds (Origanum vulgare).
Please could you confirm if these seeds are the same variety as the ones grown in the Mediterranean that have the best medicinal composition. Is it the same herb variety that the North American Herb and Spice Company use for their product of "Oil of Oregano"?

We can't comment on what exact strain of oregano the above company uses, but we believe that all of the wild oregano oils are coming from wild plants similar to our greek oregano. Our greek oregano was selected from wild plants from the mountains of Greece. It has the same strong oregano aroma and flavour as the wild types, so the oil is likely to have a similar chemical profile to those of the medicinal oregano oils that are widely marketed.
The common marjoram you purchased is not the same as the greek oregano. It does not have the same aroma and flavour. Although, confusingly, it is alternately called "wild oregano" it is far removed from the kind of oregano you want for medicinal purposes. The greek oregano is actually much closer to the "wild oregano" that the medicinal oils are extracted from.

Please would you advise me on the following:-
1. The best soil.

They like a sandy soil. In our sandy rock garden they flower and seed freely.

2. Recommended plant food for growing it in pots as well as outdoors.

Well-rotted manure added in the spring as a top dressing, is the best fertilizer.

3. The best way to grow this herb and the best time to reap the leaves for the highest composition of the medicinal properties.

This herb needs full sun and heat to develop the best oil content. Harvest the leaves just before the plants open their flowers for highest oil content. It is also recommended to harvest in the morning just as soon as any dew has evaporated, again for highest oil content.