Pumpkin problems

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.

Assisting root growth

We all know that an adequate supply of phosphorus is essential for healthy root growth but, during hot, dry months, we can further assist some of our vegetables to produce extra roots.
Pumpkins produce a huge amount of foliage – too much for the original root system to supply adequate water to the entire vine. Consequently, these plants and some other members of the squash family have evolved to produce roots at nodes (stem joints) along their runners. (See photo below.)
We can assist this auxiliary root formation by carefully lifting the runner and scratching the surface of the soil beneath where roots buds appear. Then cover this with a shovelful of compost and settle the runner back onto the compost. Encouraging extra roots to form will increase your crop.
These sections may be hidden by foliage but it will help to identify them if you place a soft drink bottle or large juice bottle (with the base removed) neck down beside this area. When watering, water not only around the base of the plant, but also into the bottles to supply water directly to the extra roots without wetting the foliage.

Tomatoes in their natural state, grow along the ground and will also form auxiliary roots along their stems, but our method of growing tomatoes tied to stakes prevents this. However, you can give them a helping hand to produce extra roots before planting out by lying potted seedlings on their side when they are 10-12 cm tall. Leave them like this for a week or so, depending on the growth rate, and remember to stand them upright for watering. As you can see in the photo, the main stem with make a 90-degree turn, and root buds will form on the horizontal part of the stem. Plant them out with the growth tip vertical and the horizontal stem just below the soil surface.
You can also hill up soil around tomato plants (a little at a time), and sweet corn plants to encourage extra roots to grow on the lower parts of the main stem.

pmpknrootstmtroots

Squash, melon and cucumber problems

A problem I am frequently asked about is why do immature fruit of the Cucurbit family become soft or discoloured, and fail to mature. The squash or Cucurbit family includes chokoes, cucumbers, grammas, gourds, pumpkins, rockmelons, squash, watermelons, and zucchinis.
If your cucurbit plant is producing small fruit that yellow and fall off before maturity, or turn mushy at the end furthest from the stem, it does not have a disease, or a pollination problem. Your plant is deficient in calcium. Calcium deficiency also causes blossom end rot in tomatoes and capsicums.
Like us, plants need a good balance of calcium and magnesium to form a strong structure. Calcium and magnesium are required for growing tips of plants as well as fruit production and, if there are not enough of these nutrients to go around, growing tips will get priority. Calcium deficiency can occur in several different ways.
Most commonly, it occurs when soil is too acid (soil pH less than 6) and there are insufficient calcium ions in the soil. In soils with a suitable pH of 6 – 7.5, erratic watering can cause it, as plants are unable to absorb nutrients from dry soil, when needed.

To avoid blossom end rot, ensure that your cucurbit (or tomato/capsicum) bed has a suitable soil pH before planting out seedlings. See Changing soil pH. If your soil is quite acidic, and the problem has already occurred, you can raise soil pH slightly by dissolving a generous handful of dolomite (a mixture of calcium and magnesium) in a full watering can, and apply this around the root area (under mulch) of each plant – one full watering can per plant, or two around large vines such as pumpkin and watermelon. If you know that your soil has plenty of magnesium, use agricultural lime instead. This treatment will take several weeks to work, so good bed preparation is worth the effort.
Where erratic watering is the problem, mulch around your plants to reduce fluctuations in soil moisture, and water plants thoroughly once or twice a week, rather than giving them a light watering every day. Pumpkin vines require a lot of water to produce a good crop.

Pumpkin update

Now that the pumpkin vine is dying off, we are able to find the entire crop – 27 pumpkins from one vine. Compost and plenty of water are the secrets to healthy pumpkin growth. Despite prolonged periods of rain, the vine has remained healthy without a hint of mildew because full access to nutrients has provided the vine with a healthy immune system. The only down side to this luxurious growth has been that it has provided a multitude of places for our chooks to hide their eggs.

Saving pumpkin seed

If your pumpkin vine has performed well for you this year, it is worth saving seed from one of the best pumpkins as the plants that grow from collected seed will have already adapted to your soil and climate conditions, and pumpkin seed is very easy to save. After harvesting, store the pumpkin for 2 or 3 weeks to make sure the seeds are fully mature. Then cut the pumpkin and scoop out the seeds. Place the seeds in water and rub them to remove the pulp. Viable seeds usually sink to the bottom of the container. Rinse the seeds well, then spread the seeds on a sheet of paper to dry where mice can’t get to them. After two weeks, place seeds in a labelled jar or envelope and store in a cool, dark, dry place.

Harvesting pumpkins

Pumpkvine.jpg
It’s about time to harvest pumpkins again. Our pumpkin vine this year was a volunteer that sprang up in the chook run from the remnants of an old compost heap. It didn’t get any TLC because we half expected the chooks to trample it before it became established. However, it defied the odds and performed magnificently – which only goes to show how good compost is for growing vegetables.
I think it was only watered once but it received plenty of rain during its growing period, and the vine has produced at least 14 JAP pumpkins that we have found so far. JAP pumpkin is closely related to butternut pumpkin, gramma and trombone squash (Cucurbita moschata). These are thinner skinned and don’t keep as long as the Queensland Blue types (C. maxima).
Because we couldn’t spare the water last year, we bought all our pumpkins and some of them weren’t the best because of the drought. Consequently, we were curious to see what we could expect from our volunteer plant and picked one of the pumpkins early. (As you can see in the photo below, the stem is still moist.) Pumpkins picked at this stage do not keep well but we are using this pumpkin immediately, so it doesn’t matter. Now that they are nearly ripe, we will put a broken piece of foam box or thick cardboard under each fruit to keep them drier and clear of the ground, so they are less likely to rot. We will be leaving the rest of the crop until the vine dies off, and the stems become brittle, as that is when they develop their full flavour and store well. If you can’t wait that long, at least wait until the tendril closest to each pumpkin browns off.
Don’t worry about frost on your pumpkins, it will only kill the vines, and it is said that frost toughens the skins so that pumpkins keep longer.
P.S. When the vines had died back a bit, we realised that the vine had produced 28 pumpkins. Not bad for a volunteer vine! There were, of course, more than enough to supply family and friends, and we were able to sell the rest through our local organic greengrocer.
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No crops on cucumbers or squash?

This post has been updated. See Squash family not forming fruit?

The squash or Cucurbit family that includes chokoes, cucumbers, grammas, gourds, pumpkins, rockmelons, squash, watermelons, and zucchinis, produce both male and female flowers on the same plant, and rely on insects, such as bees, to pollinate the female flowers and produce fruit.
Although we eat many of this family as vegetables, in gardening terms, their produce is fruit.
With large areas of Australia experiencing prolonged overcast weather, and other areas experiencing smoke from bush fires, bee activity tends to be reduced and cucurbits may not be cropping. In circumstances like these, you may have to hand pollinate your plants to reap the benefits of your hard work. This is quite a simple procedure.
First identify the the female flowers on your vine or bush. At the base of each female flower you will find a miniature version of the mature fruit of that particular species. For example, cucumber vines produce what looks like a tiny gherkin at the base of each female flower while watermelon produce a watermelon miniature, often complete with stripes. The bases of male flowers, on the other hand,
join directly onto a vine stem.
Remove a male flower from the vine, and carefully peel back the petals so that the pollen bearing part in completely exposed. Then dab the centre of the male flower into the centre of a female flower. Repeat this process, replacing the male flower as pollen is removed. Then stand back, and allow nature to take its course.

If you can only find male flowers on your cucurbit vine, the problem takes a little longer to overcome. Pinch off the end of each long runner. This will stimulate the plant to produce side shoots called laterals. Some members of this family tend to produce female flowers on laterals. Once female flowers form, proceed with hand pollination if there are not many bees around.

If your cucurbit plant is producing small fruit that yellow and fall off before maturity, or turn mushy at the end furthest from the stem, you have a different problem altogether. Either you do not have enough calcium in your soil, or watering has been erratic and calcium has not been available when needed. Like us, plants need a good balance of calcium and magnesium to form a strong structure. Calcium and magnesium are required for growing tips of plants as well as fruit production and, if there is not enough of these nutrients to go around, growing tips will get priority. Dissolve a generous handful of dolomite (a mixture of calcium and magnesium) in a full watering can, and apply this around the root area of each plant – one full watering can per plant, or two around large vines such as pumpkin and watermelon. If you know that your soil has plenty of magnesium, you can use agricultural lime instead. §