How to Grow Pumpkins

Pumpkins are native to tropical regions of South America. They bear large fruits and so naturally need a large growing area.  They have edible firm flesh encased in a tough outer coating. Pumpkins have a similar appearance to marrows with regards to their growth habit. That is, they are bushy to trailing plants and their leaves are large, mid-green, heart-shaped and lightly covered with short hairs. The flowers are yellow to orangey yellow coloured and bell-shaped. The fruits are variable and have outer skins in shades of dull greyish yellow though to bright orange. There are also some varieties with white, bluish or green skins. They may be smooth or furrowed and rounded to vase-shaped. Pumpkins range in weight from small types at about 5 pounds (2.3kg) through to the largest weighing in at 100 pounds (45kg). The latter types are usually the ones grown for giant vegetable competitions and garden fetes. Some are grown primarily for their seeds which are roasted.

The terms pumpkin and squash often refer to plants which belong to the same botanical classification. What is termed a pumpkin in Australia, New Zealand and the UK refers to the broader shaped fruits of Cucurbita maxima.  In the US these are called “Winter Squash”.  However, there is no agreed botanical system to distinguish squashes and pumpkins. Therefore the names are often used interchangeably.  In the UK and Australia the name 'squash' is often preserved for irregular and often quite unusual shaped fruit.

Many pumpkins come from the group Cucurbita pepo e.g. 'Delicata', 'Acorn', and 'Jack O' Lantern'. Most of the larger varieties like the giant types come from C. maxima e.g. 'Big Max' and 'Giant Atlantic'. Others come from C. argyrosperma e.g. 'White Cushaw', and from C. moschata e.g. 'Butternut Hercules'.     

Growing Conditions
Pumpkins require similar conditions to cucumbers except that the soil doesn't need to be quite as warm for seeds to germinate. Temperatures of 12-15°C and over are usually suffice for germinating most types but it's important to know the temperature range for the specific type you're growing. Prepare the soil beforehand around the end of winter by digging out holes 30-40cm deep and wide. Mix in plenty of well-rotted manure or compost into the soil and backfill. A soil pH of 6-7 is ideal.

Culture
Position seedlings or plant out the seeds in a position where they will receive full sun. In temperate climates planting will coincide with about mid spring. In warmer regions it will be earlier. It is a good idea to harden off young seedlings in a cold frame in cooler regions before planting them out in vegetable beds. In these areas plants can be put in their final positions towards the end of spring or a slate as early summer. If sown directly in cooler regions cloches may be placed over seedlings until temperatures have warmed up and the last chance of frost has elapsed.

Once established they are reasonably hardy and secondary vines will re-grow form damaged vines. To promote the growth of lateral shoots which bear most of the female flowers the growing tips of trailing varieties can be pinched back. This will also help to contain trailing types. In some cases it may be necessary to aid pollination by brushing pollen form male flowers onto female flowers.  

Apply a layer of organic mulch to preserve soil moisture and keep the roots warm. Water plants well throughout the growing season. You can try laying ground fruits on a layer of straw to stop rots, mildews and viruses from passing to them from the soil.    

Planting
Plants should be spaced at 40-50cm for smaller bush types through to 1 to 1.2m for trailing types. Of course you should space them according to recommended spacing for the variety. If they are allowed to trail across the ground then you will need more ground space. Bush types and shorter vines are more suited to smaller gardens.  

Pest and Disease Problems
Pumpkins are a lot less difficult to grow than cucumbers. They are however prone to some of the same diseases. In particular, watch out for cucumber mosaic virus which causes mottling of fruits and distortion. They may also become covered with lumpy spots. Powdery mildew can cause the formation of a white powder-like substance on the foliage and fruits. Downy mildew may leave a greyish white velvety coating on plant parts. The risk of rots, moulds and mildews may be reduced by good aeration and keeping fruits raised on straw mulches.      

Harvest

Typically, fruits mature between 10 to 15 weeks depending on conditions and variety. In the main, those with larger fruits are left on the vine to mature for longer and many of these will be left to harvest until the autumn providing crops for winter use. Smaller fruiting types will be cropped earlier as they reach maturity. They can be removed from the vine when the stem starts to shrivel. If you wish to produce fruit for shows then remove all but one fruit and allow the plant to put all its energy into that one fruit. Fruits should be cold stored at 10°C or less.