Karen has had disappointing results from her Queensland Blue pumpkin vine which produced pumpkins with very little flesh and she wants to know how to avoid problems in future.
Karen, if the seeds are soft and immature, you may have picked the pumpkins before the ‘fruit’ has fully developed, and pumpkins are fruits although we call them vegetables. However, if the seeds are mature, a common cause of this problem is hunger, and this can occur in several different ways even though you may have thought that the plant was well fertilised.
If soil is not damp, nutrients can’t be absorbed by the roots. If soil pH is too acidic or alkaline plants will go hungry because the soil pH controls which nutrients are available to plants, and pumpkins need a soil pH of 5.5-7 for good growth. Pumpkins vines can produce an enormous amount of foliage – and it is a huge task for the roots at the base of the vine to provide moisture and nutrients through the whole plant. When pumpkin vines are allowed to wander over soft earth, they will usually put down extra roots along the vines to assist with water and nutrient absorption.
You can encourage the formation of extra roots, see Assisting root growth.
Pumpkin flowers are pollinated by bees and occasionally a flower or flowers can be pollinated by pollen from a cattle pumpkin, which usually results in fruits that are tough and pretty tasteless. (If your neighbours are growing cattle pumpkins, you may have to hand-pollinate pumpkin flowers).
I’d advise you not to save any seeds from pumpkins that have little flesh or tough flesh as any vines grown from these seeds will probably produce poor quality crops. Only use seed from your best home produce or purchase seeds from a reputable supplier.
Pumpkins thrive on compost, so make compost through the winter ready for next season’s vines. Turning the heap a couple of times a week will keep you warm, keep the heap aerated, and speed up the composting process. If you live in a cool climate, put some black plastic over the top of the heap to help absorb heat. Use the compost to get your pumpkin vine off to a flying start in a different spot in your garden when soil warms in spring.