The production of pumpkins and squashes

Pumpkins and squashes belong to the family cucurbitaceae and are related to calabashes, watermelons and muskmelons. Pumpkins and squashes probably originated in America from where they spread to Europe and other parts of the world. Pumpkins were introduced to South Africa when the first Europeans arrived and they imported the seed from Brazil.

An interested fact about pumpkins is that both male and female flowers are carried on the same plant.

The common names of the different species in the Genus Cucurbita cause considerable confusion. The botanical types which are of economic importance are Cucurbita Maxima (pumpkin), Cucurbita Pepo (squashes) and Cucurbita Moschata (butternut). In South Africa ‘Flat White Boer’ and Queensland Blue are classified as pumpkins, while Green and Golden Hubbard are wrongly called squashes. To prevent confusion, in this article the term pumpkins will refer to Cucurbita Maxima.

Cucurbita maxima (pumpkins) varieties:

• Flat White Boer
• Queensland Blue
• Green and
• Golden Hubbard

Cucurbita pepo (squashes)

This includes Gem Squashes, Baby Marrows, Table Queen, Golden and White Custard. The growth habits vary from short stem which creates a busy appearance such as Caserta, to the wide trailing varieties Rolet and Little Gem. Many F1-Hybrid squashes are also available. Varieties such as Ambassador, Embassy, Gold Rush, President, Zenith, Sundance and many more.

Cucurbita Moschata

The best-know variety are the Butternut Ceylon “Pumpkins”, Rovaal and Roverberg. Rovaal is a cylindrical type or more or less a watermelon with an excellent yield and keeping quality.

Climatic requirements of pumpkins and squashes

Soil temperature

The minimum soil temperature for good field germination is approximately 18°C and the maximum 30°C. Seed germinates poorly below 16°C. No germination takes place at temperatures below 10°C.

Air temperatures

Cucurbits are sensitive to frost and are injured at -2°C. Almost no growth takes place at temperatures below 15°C. Plants generally grow more luxuriantly at higher temperatures.  At extremely high temperatures only male flowers may be formed. Varieties with dark-skinned fruit are highly susceptible to sunburn. The most effective protection is obtained when the fruit are totally coved by foliage. A good foliage can be maintained by good cultivation practices.

The length of the growing season from planting to harvesting is more or less as follows.

• Marrows: 60 – 75 days
• Butternut: 90 – 100 days
• Pumpkins: 120-150 days

Humidity

Areas with high humidity during the growing season can be plagued with fungal diseases especially at the end of the growing season. In these areas production is dependent on a highly effective spray program.

A long rainy period just before or during harvesting can cause the fruit to rot, especially on heavier soils.

Soil requirements

The best results are obtained on a loamy to sandy loam soil. Heavy soils that do not drain well should be avoided. The surface of such soils remain damp too long after rainfall or irrigation and aeration of the soil is limited. The end result is fruit that rot on the field.

Pumpkins and squashes prefer slightly acidic soils.

As far as soil acidity goes, good results can be expected over a wide range pH range, typically between 5.5 – 7.5. If the soil is more acidic, less than 5.5, dolomitic agricultural lime must be applied according to a soil analysis. Work the lime 4 weeks before planting into the soil.

The ideal soil-depth for pumpkins and squashes is 400 mm. The highest concentration of roots are found in the top 200-300mm of soil. Tillage banks and impenetrable layers at less than 400 mm must be broken.

Fertilizer requirements

Because of diversity of soil types, it is not possible to give a standard fertilizer recommendation. Fertilizer recommendations must be based on soil analysis. Following a general guide is dangerous but if you don’t have anything it is better than nothing.

Pumpkins and squashes react favourably to a high organic matter content in the soil. If kraal manure or compost is available it can be worked into the soil. For soils low in phosphate at least 300 kg/ha super phosphate or 80 kg/ha urea must be applied in addition to the kraal manure.

If required, an additional topdressing of 100-150 kg/ha LAN or 60-70 kg/ha urea can be applied just before flowering. Normally a single topdressing is enough and can be applied approximately three weeks after emergence.

If kraal manure is not available the super phosphate must be increased to 500 kg/ha and 250 kg/ha LAN.

Applying the fertilizer to pumpkins and squash fields.

Pumpkins and squash are planted in rows. Your first pre-plant application will be broadcast but subsequent post emergence fertilizer applications must be placed in the rows of both pumpkins and squash. Once the roots have developed and spread can one apply a last application broadly.

There is no use in broadcast fertilizer applications if the plant cannot utilize the nutrients. The nitrogen will be consumed quickly by bacteria and lost to the plant. So basically you have fed some bacteria and it has not gone into producing good yields.

Planting time of pumpkins and squashes

Pumpkins and squash can be planted from early spring to mid-summer. Remember they are summer crops and have soft leaves and stems which are easily damaged by frost and even extreme hot conditions.

Insect populations such as pumpkin fly and aphids increase as the season progresses. The pumpkin fly lay their eggs just under the skin of a young fruit and this gives rise to the characteristic lesions on the fruit, white maggots are found inside the fruit at a later stage. Aphids on the other hand carry the mosaic virus and infect plants as they feed. High humidity during summer cause serious problems with leaf diseases. These insects and diseases can be avoided by planting early in the season.

The earliest planting date is when the soil temperature has risen to about 18°C and there is no danger of frost. Even at 18°C the seed germinates slowly and poor stands may be obtained if poor weather sets in. Seed trays can be used and kept in warm place for early plantings. Select early varieties or cold resistant varieties when planting early.

Planting method

As has been mentioned before, pumpkins are planted in rows and not broadcast like wheat or barley. The general guideline for in row planting are:

• Pumpkins: 2.1 – 2.7 m rows and 0.7 – 0.9 m in the rows
• Marrows: 1.2 – 1.5 m rows and 0.5m in the rows
• Squash, butternut: 1.2 – 1.8 m rows and 0.5 m in the rows.

The spacing may be adapted to some extent according to climatic conditions and available implements. These are just a guide line.

Two to three seeds are sown together at given distances within the rows.  The reason why more than one seed is planted is to ensure a good stand since pumpkins and squashes normally cannot be transplanted. Seedlings that have been establishsed in pots or seed trays can however the transplanted after two or three weeks. The seedlings are thinned out to single plants by cutting the stem off.

As with other vegetables, pumpkins and squashes can also be planted in seedling trays with slightly larger holes. Seed trays are used with expensive F1-hybrid varieties.

The seed must not be planted deeper than 30-40 mm (3-4 cm). Under ideal conditions the field should be irrigated well before planting, irrigation should not be applied before emergence as this may cause the formation of a crust on top of the toil preventing the cotyledon from emerging.

The seed should not be planted too shallow as the top layer of soil will dry out quickly, resulting in poor field germination.

Methods of establishment

Pumpkins and squash can be established by various techniques. The method will depend on the humidity and rainfall of the area and the type of soil, implements and irrigation system.

Planting on level ground: Fertilizer can be broadcasted or placed in rows using a disc plough or rotovator. The seed or plants are planted on a level surface with no further cultivation.

Furrows: Furrows are use where fertilizer Is applied by hand in the rows or where flood irrigation is used. Furrows are drawn at the required spacing by means of suitable implement. Fertilizer is applied in the furrows and is lightly mixed with the soil in the middle of the furrow channel. The furrows can now my irrigated using flood method. The seed or plants can then be planted just above the level at which the water flows.

Planting holes: If very little irrigation water and soil are available, pumpkins and squash can be planted in holes. Fertilizer compost or manure can be spread in a circle ±700 x 700 mm and worked into the soil. A ridge is made around the hole to keep water in. Water can be applied with a bucket or hose.

Weed control

The roots of cucurbits are shallow and spread widely. As a rule of thumb the roots spread as wide as the leaves and stems grow. They develop at the same rate and in the same direction as the vines. Weeds must therefore be controlled by shallow cultivation to prevent damaging the roots. If a hoard crust develops, usually after heavy rain, the curst should be broken between the rows during the first 5-6 weeks. Weed control at a later stage may damage the plants and is not necessary as dense foliage tends to smother weeds.