Without doubt the most exciting time in an asparagus plantation is when the spear harvest is underway. In the UK, this is spring time between April and June. Once the picking has finished, it is time for the fern to grow away. Many people then forget about the asparagus bed, save for a little weeding, until the following spring's harvest. However the fern growth period is absolutely crucial in the development of the asparagus plantation.
To sum up very briefly, the better the fern growth, the higher the yield potential for the following season's spear harvest. To understand the importance of the fern growth period, perhaps it is a good idea to hark back to GCSE / O Level Biology. It is a question of simple photosynthesis. For those that are interested, the equation we had to memorise was as follows:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Carbon dioxide + Water + Light energy → Glucose + Oxygen
Before you ask, yes I did have to look that up before committing it to this blog...
But why is this important in asparagus?
The asparagus fern intercepts light that brings about photosynthesis within the asparagus plant. This light is synthesised with the resultant product being Carbohydrates (CHO). As the fern senesces during autumn and winter, the CHO is returned to the asparagus root system. It is then this CHO that is turned into energy to increase the size of the crown and drive the yield potential of that asparagus plant. Resultantly, the better the fern of the plant, the better the photosynthesis and the higher the yield potential the following spring.
That is the science bit over for now...
So in practical terms, what can an asparagus grower / gardener do to improve the fern quality of their crop?
Asparagus fern is susceptible to a whole range of fungal diseases that will cause it to senesce early, thus reducing photosynthesis and crop potential. It is therefore very important to keep the fern healthy. Important asparagus fern diseases are Stemphylium (purple spot) and Botrytis (grey mould). As with most plant diseases, prevention is always better than cure. In asparagus, this means to sufficiently bury, remove or destroy the old fern after it has died off. If it is left around the crop, new fungal spores will be encouraged to reform and they will naturally attack the newest, juiciest looking green fern. Some weed types are also hosts to these asparagus diseases, so it is vey important to keep your plantations weed free. If disease does get into the crop, there are options to control using sprays. In fact, large scale growers will have specialist equipment that travels over the asparagus fern and sprays just where it is needed.
The basic aim is to keep the fern as green as possible for as long as possible to ensure maximum crown development and yield potential for the following spring.
Once the fern has died off in the winter, it is important to remove it at the right time. As a good rule of thumb, the fern is ready for removal once it has become brittle enough to be easily snapped between thumb and forefinger. It should then be cut off at the base, as close as possible to the soil surface and either removed, destroyed or buried.
If these practices are maintained, they will not only increase asparagus yields but also improve the longevity of your crops.
Now I know why I should have paid more attention in those Biology lessons, but better late than never...