First off some quick basics. Asparagus is a long lived (about 20 years) perennial, so it needs to be located in the garden where it can live out its life for many years to come. While it can be readily transplanted, it will take time to recover from the move, meaning less fresh asparagus in the kitchen (if it even makes it that far). Asparagus does well in a sunny position, but it can also handle some shade during the day and still perform well.
As James stated in one of the comment responses, asparagus loves a deep rich well drained soil. Of those adjectives, well drained is the most important. Poorly draining soil can result in root rot. So don't dig a pit into clay soil, particularly in sub/tropical areas with heavy seasonal rains.
Asparagus is tough, it can grow just about anywhere. If a seed is able to germinate in a crevice between two rocks, it will and will do quite fine thank you very much. That said, you want eat the new shoots, so giving it deep rich soil will allow the plant to produce more spears more often. And more spears means more tasty dishes.
Asparagus is happiest in a neutral soil pH between 6.5 and 7.5. If the pH starts getting below 6.0, then it will start to suffer. As mentioned previously, asparagus likes rich soil, but particularly rich in phosphorus and potassium. So make sure you given them fertiliser rich in phosphorus and potassium when planting. In fact (as I have also proven), the roots can handle being directly on the fertiliser.
Asparagus should be planted about 12.7 cm to 15.3 cm deep. Any deeper will result in a decreased yield. This information is quite different to what the majority of web sites or even "experts" will tell you. Ohio State University is to thank for this tidbit.
Of course the next question is how close to plant them. Again the information in this area can vary considerably, however with good reason. You need to know how you plant to harvest your plants, how rich the soil is, and what other competition exists. In ideal conditions, they can be planted as close as 15.2 cm. That right, 15.200000 cm. This tidbit is from John F. Kelly, J. Bakker, Hugh C. Price, and Norman L. Myers. This means you can get your 20+ asparagus into a small area and get a better yield of harvest. This is much smaller area than what the Gardening Australia fact sheet on asparagus tells you (in fact much of the information there is out of date).
So what did I do when I planted my 80-some home grown seedlings out?
- I prepared the soil as well as I could (see the Asparagus Galore post).
- I used individual holes for planting out the seedlings as opposed to a furrow (purely by choice).
- I offset the rows resulting in a diamond type planting pattern. The spacing between the plants was no closer than 30 cm partly due to the state of the soil prior to improvement. As a future experiment, I will plant some new seedlings in the centre of the diamond (giving a 15 cm plant spacing) to see what the result is.
- The plants were planted about 10 cm deep which is even shallower than recommended. This was on purpose as I figure I can always add more compost over time.
- I added chicken manure to each of the planting holes. While I did not hold the chooks bum over the asparagus seedling hole, it was freshly collected during the days prior and even on the day.
- The roots were not spread out during planting. There is no need to do this as it makes no difference to the growth of the plant.