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General - Length of Growing Period
The correct choice of planting time is one of the most important decisions that a vegetable producer needs to make. It can be critical as far as crop yields and quality achieved are concerned. It can have an important bearing on various costs of production, such as the costs of insect and disease control. Moreover, it determines the season of harvest, and this normally affects prices received for the product.
The climatic requirements of the crop should be matched to the expected conditions applicable to the specific production site selected, if a successful crop is to be produced. In addition, production should, if possible, be aimed at a time of year when remunerative prices are more likely to be paid.
In order for plant growth to take place during favourable conditions, and when aiming to harvest at a specific time, it is essential to know approximately how long it will take the crop to reach market maturity, as well as the length of the cropping season. Obviously these timespans will vary, depending upon the crop concerned and the cultivar, the cultural practices applied , and the environmental conditions prevailing during growth.
Effects of Temperature
The prevailing atmospheric and soil temperatures play a major role in determining the length the of season for any cultivar.With the exception of lettuce and spinach, most vegetables will either not germinate, or will take a month or longer to emerge, when temperatures are kept at only 5șC.
At 10șC most cool-season crops such as beetroot, carrot, celery, the cabbage family, the onion family, peas, radish and turnip will germinate satisfactorily and generally take 10 to 20 days to emerge.
At 15șC most crops will germinate well and should emerge within 10 to 20 days, except for crops such as Lima bean, okra and peppers, which may take up to about 30 days.
Between 20șC and 30șC most crops will emerge within 4 to 14 days, an exception being celery, which does not readily germinate at temperatures of above 25șC.
At 35șC emergence problems can occur with many cool-season crops, although beetroot, carrot, the onion family and turnip should still emerge well and rapidly.
At 40șC only okra and turnip are likely to emerge satisfactorily. Most vegetable seed will sprout and emerge fairly rapidly at soil temperature varying from 15șC to 30șC.
The effects of temperature on time from seeding to plant emergence are illustrated in Table 2 (see Climatic Requirements). These emergence periods will normally be extended with deeper plantings, as is often the practice with vegetables with larger seed, or under drier conditions. Soil temperatures are lower with depth, and the shoot tips have a greater length of growth in order to reach the soil surface. Prevailing temperatures will also affect other growth stages of plants.
The average growing and harvesting periods of various vegetable crops grown under optimum conditions are listed in Table 4 . As conditions seldom remain optimal for the full growing period, most crops will, in practice, be later-maturing than indicated in the table. Delays should be expected with plantings made early in spring or very late in the normal growing seasons, when conditions are not as favourable for growth.
For example, a green bean cultivar may reach maturity in 60 days when grown over summer, but may need 85 days when planted under the cooler conditions prevailing in early spring. This could result in the next planting of the same cultivar, made 2 or even 3 weeks later (when conditions might be more favourable for growth), reaching market maturity within a few days of the earlier planting.
Most other crops will be similarly affected by changes in temperature, day-length or some other factor which could influence rate of growth or development.
Table 4: The approximate times required from planting to first harvest (under optimum growing conditions) and length of the harvesting period of some vegetable crops. Periods will vary with cultivars.
Vegetable
Days to First Harvest
Usual Harvesting Period
Bean, broad
120
2 months
Bean, green, bush
48 - 60
2 -3 weeks
Bean, green, runner
62 - 68
4 - 6 weeks
Bean, Lima, bush
65 - 78
3 - 6 weeks
Bean, Lima, pole
78 - 90
2 - 4 months
Beetroot
56 - 70
3 - 5 weeks Brinjal
60 - 85 *
2 - 3 months Broccoli
50 - 80 *
Heads 1 - 2 weeks
Sprouts 3 - 4 weeks longer Brussels sprouts
100 - 120 *
2 - 3 months
Cabbage
65 - 120 *
1 - 4 weeks
Carrot
80 - 120
1 - 4 weeks
Cauliflower
60 - 130 *
2 - 4 weeks
Celery
90 - 125 *
2 - 4 weeks Chilli
65 - 80 *
2 - 4 months
Chinese cabbage
70 - 90
1 - 4 weeks
Chives
90
Until replant
Cucumber
60 - 70
1 month
Kohlrabi
50 - 60
2 - 4 weeks
Leek
150
1 - 2 months Lettuce, butter
45 - 70 *
1 - 2 weeks
Lettuce, head
50 - 80 *
1 - 2 weeks
Marrow, baby
40 - 50
6 - 9 weeks
Marrow, large
70 - 80
4 weeks
Melon, musk/sweet
80 - 110
2 months
New Zealand spinach
70
2 months
Okra
50 - 60
4 - 6 weeks Onion, table
140 - 180 *
200 - 250 direct sowing
1 - 4 weeks
Onion, pickling
70 - 100
1 - 4 weeks
Parsley
70 - 80
4 - 10 weeks
Parsnip
120
2 - 4 weeks
Pea, green
60 - 80
2 - 3 weeks
Pepper, sweet
65 - 80 *
2 - 3 months
Potato
90 - 120
2 - 4 weeks
Pumpkin
110 - 130
1 - 2 months
Radish
20 - 30
1 - 2 weeks
Spinach, true
40 - 55
1 - 2 weeks
Squash
85 - 110
1 - 2 months
Sweet corn
70 - 90
1 - 2 weeks
Sweet potato
90 -150
1 - 2 months
Swiss chard
50 - 60
2 - 4 months
Tomato
75 - 90 *
2 - 3 months
Turnips
45 - 75
2 - 4 weeks
Watercress
180
Until replant
Watermelon
75 - 95
1 - 2 months
* denotes time from transplanting
Note:
For crops such as cabbage, carrot, lettuce, onion and potato, the entire crop may be ready for harvesting within a few days but is usually done over a longer period. If the cultivar grown is a hybrid, the harvesting period will probably be more restricted than is the case with an open- pollinated variety.It must be emphasized that the above periods will vary with cultivar, as well as with variations in environmental factors. Maintenance of records of each planting eventually will enable any grower to forecast, fairly accurately, when any specific planting is likely to reach market maturity, as well as the duration of the harvest. Such information is an invaluable aid in future planning.
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