The choice of cultivar
is an important decision that has to be made
before growing starts. There are many possibilities for each crop,
but a major consideration is the need for uniformity. Where this is
important, e.g. for 'once over harvesting' or uniform size, then F1
hybrids are normally used even though they are more expensive. Required harvesting dates affect not only sowing dates but the
selection of appropriate early, mid-season or late cultivars. Other factors
for choice include size, shape, taste, cooking qualities, etc. Examples of
carrot types to choose from are given in Table 1.1.
|Table 1.1 Types of carrot shapes
Most vegetables are grown in rows. This helps with many of the
activities such as thinning and weed control. Seeds are often
sown more thickly than is ideal for the full
development of the plant;
this ensures there are no gaps in the row and extra seedlings are removed
before plant growth is affected. The final plant density
the crop concerned, but it is often adjusted to achieve specifi c market
requirements, e.g. small carrots for canning require closer spacing
than carrots grown for bunching. The arrangement of plants is also an
important consideration in spacing
; equidistant planting can be achieved
by offsetting the rows (see Figure 1.3).
Seeds are often sown into a separate seedbed or into modular trays
until they are big enough to be planted out, i.e. transplanted, into their
fi nal position. This enables the main cropped areas to be used with a
minimum of wasted space. It is also a means of extending the season
and speeding up plant growth by the use of greater protection and, where worthwhile, with extra heat. Larger plants are better able to
overcome initial pest or disease attack in the fi eld and also the risk of
|Figure 1.3 Spacing of
plants in rows; offset
rows to the right and
mature plants to the
(the growing of one crop in between another) is uncommon
in this country but worldwide is a commonly used technique for the
- to encourage a quick growing plant in the space between slower ones
in order to make best use of the space available;
- to enable one plant species to benefi t from the presence of the others
which provide extra nutrients e.g. legumes;
- to reduce pest and disease attacks.
Continuity of supply can be achieved by several means, most usually by
- selecting cultivars with different development times (early to late
- by using the same cultivar but planting on different dates.
These options can be combined to spread out the harvest and which can
be achieved with some accuracy with knowledge of each cultivar and the
use of accumulated temperature units.
After the crop is established, there are many activities to be undertaken
according to the crop, the production method and the intended market.
These operations include:
- weed control
- earthing up e.g. potatoes and leeks
- pest and disease control. This is essential to ensure both the required
yield and quality of produce.
The stage of harvesting is critical depending upon the purpose of the crop.
Recognizing the correct stage to sever a plant from its roots will affect its
shelf life, storage or suitability for a particular market. Some vegetables
which are harvested at a very immature stage are called 'baby’ or 'mini'.
The method of harvesting will vary; wholesale packaging requires more
protective leaf left on than a pre-packed product. Grading may take place
at harvesting, e.g. lettuce, or in a packing shed after storage, e.g. onions.
An understanding of the physiology of the vegetable or plant
material being stored is necessary to achieve the best possible results.
Root vegetables are normally biennial and naturally prepared to
be overwintered, whether in a store or outside). Annual
vegetables are actively respiring at the time of picking, but
with the correct temperature and humidity conditions the useful life can
be extended considerably. Great care must be taken with all produce to
be stored as any bruising or physical damage can become progressive
in the store. Dormant vegetables can be cold stored, but care must be
taken to prevent drying out. For this reason different types of store are
used depending on the crop; ambient air cooling is used for most hard
vegetables and refrigeration for perishable crops gives a fast pull-down
of temperature and field heat.