Butternuts are a type of winter squash, as while they grow over the Summer and Autumn,
most varieties will store for three or four months over the winter, in a cool dry
Butternut Squash are from the Americas, and may have been cultivated for well over
7500 years by the Native Americans. The word “Squash” comes from the native word
“askutasquash”, which apparently means “the green thing to be eaten raw”. though
we prefer them cooked!!
Butternuts have unfortunately been mostly derived from Cucurbita moschata, which
prefers longer and hotter summers than are routinely likely for much of the UK. There
is much “weeping and wailing” on the vegetable growing forums, from those who fail
to get their semi-tropical Butternuts to set fruit or harden off before the Autumn.
This is not surprising as there is a very limited time available to carry this out,
especially in the North of the UK.
They cannot be planted out before the last frost in late May or early June without
cloche protection. The Butternuts must be hardened off before the first frost of
the Autumn in possibly late September. This gives an available “growing window” of
some 105 days, whereas the traditional varieties of Butternuts are likely to take
some 125 days before even the first Butternut is ripe! Therefore, even though new
varieties, specially bred for the UK climate, are becoming available, it is still
a challenge to grow mature, hardened-off butternuts in the North of the UK, unless
with some protection or in a very sheltered, sunny spot.
While this situation can be frustrating, remember that it is quite easy to grow the
alternative type of Winter Squash, derived from cucurbita maxima and cucurbita pepo,
in the North of the UK. Some of these Winter Squash varieties can be just as sweet
Your best chance of success with Butternuts in the North of the UK, would be to start
the seeds of one of the specially bred, early ripening Butternut varieties indoors
in a propagator in April, transfer the seedlings to a greenhouse, then cold frame,
before planting them out in early June under cloches or a purpose made cold frame.
In cold weather in April, even in a mini greenhouse within a greenhouse, the Butternut
seedlings can show signs of distress, while the pumpkin type of Winter Squash seedlings
grown in the same conditions are happy.
Warning. On no account plant out these sub-tropical plants before the last expected
date for frost in your area. This could be mid May for the mildest areas such as
Southern coastal areas, and early June in the North of the UK. Even then, provide
cloche or fleece protection for the first few weeks as cold nights and winds will
cause plant damage. Gardeners are regularly caught out by late frosts occurring during
the traditional cold period known as “The Ice Saints”, usually just before mid May.
Remember, one night of a late frost will kill your sub-tropical plants!!
When the plants start to flower, it is usual for several male flowers to appear before
the first female flowers form with an embryonic butternut underneath the flower.
You will then need to provide access for the bees to carry out the pollination, unless
you are prepared to hand pollinate the female flowers, as shown in the photo on right.
Pick the male flower when the pollen is “mobile”, and carefully strip off the petals.
Insert the pollen bearing male anther(yellow) into the middle of the female stigma(orange),
making sure that the pollen grains are transferred. Alternatively, use an artist’s
brush to transfer the pollen from the male anther onto the female stigma. Normally,
this is only effective where the male and female flowers are from plants of the same
species. Ie, both plants are cucurbita moschata, but can be different varieties.
(The example of a cross between species given below, squashkin, will have been achieved
with specialised laboratory techniques).
When a squash has quite clearly set and is growing in size, remove the dried up remains
of the flower petals to prevent them rotting in damp conditions.
In the South of England, there are many reports of success in growing Butternuts.
Start the seeds indoors in a propagator in April, transfer to a greenhouse, then
cold frame, before planting out in May or June under cloches.
The ground should be fertile and kept well watered during the growing season. The
plants can trail for several metres in a season. Therefore plenty of space is required.
You can stop them after they have set the first few fruits, which will keep them
under control and which will encourage the plants to ripen the squashes. As the squashes
form, a slate or tile should be placed under each one to keep them off the ground
and prevent rotting.
The squashes should be ready for drying off in late September or October. Cut off
the fruits leaving plenty of stem attached to prevent rot reaching the butternuts.
Place them in a dry sunny shelf in the greenhouse or sunny windowsill, for several
weeks. This hardens the skin and improves the eating quality by reducing the water
content. Once the skin has become hard, they should be stored in a cool, frost free,
dry place indoors, where they should remain in good condition until Spring. Check
your stored squashes weekly and use up any that are showing signs of the skin breaking
Pests and diseases on Butternuts.
Slugs and snails can cause a lot of damage to the main stem, particularly immediately
after you have planted out the young plants. Apply slug pellets immediately after
Red spider mite can hide on the underside of the leaves, and cause so much damage
that the leaves start to wilt in the sun, even though the plant is well watered.
Regularly check the underside of the leaves and spray as necessary.
Powdery Mildew can also be a problem in late Summer or Autumn, when you may see a
white flour-like covering to the leaves. If it occurs, it will probably be late in
the season, when the butternuts are hardening off, and it can probably be ignored.
If you need to keep the plants growing for as long as possible, you can use a fungicide.
Wind damage. Obviously not a disease but it can cause physical damage through which
other rots can start. It usually shows itself as a longitudinal crack up to 5 cm
long through the main stem, caused by the wind catching the large leaves and twisting
the stem backwards and forwards. It is easy for the young plants to become “leggy”
while they are in a greenhouse or cold frame before planting out in their final position.
Take great care while handling the plants at this stage to minimise this damage.
Once planted out, peg the stems with a cane or better still, grow under cloches for
the first month.
Suggested Butternut Type Squash varieties.
There has been a breeding breakthrough with a new butternut (cucurbita moschata)
crossed with a Winter squash, Crown Prince F1 (cucurbita maxima). When trialled last
year, in Glasgow, it set fruits at least a month before the previously available
fastest butternuts. It was only protected for the first month with a mini-tunnel.
This is my choice if you wish to grow a butternut type of squash.
Squashkin, also to be known as Autumn Crown. Produces a slightly mottled, buff coloured,
thin skinned fruit, shaped like a slightly smaller Crown Prince and weighing up to
1 Kg. The fruits have a large amount of useable orange, very sweet flesh which smell
of melon when freshly cut. Trailing vine up to 4 m.
Varieties especially bred in the UK for the UK climate, and claimed to ripen about
four weeks earlier than traditional varieties, are available as follows:-
Harrier F1. Claimed to be ready to harvest in 95 days from sowing, but expect longer
in the North of the UK. It has sweet flesh, good storage and about 800 g or 1.75
Hawk F1. Claimed to be quick maturing with sweet flesh, good storage and about 700
g or 1.5 lb size.
Hunter F1 Claimed to succeed as far north as Lancashire, with sweet flesh, good storage.
Having successfully grown the three varieties above, specially bred in the UK during
a dull, cool and wet Summer in Glasgow, growing them both under cloches and in the
open, my advice would definitely be to grow them under cloches in the North of the
UK. Harrier F1 produced the most fully ripe fruits, as it tends to set the fruits
earlier. However, they are all likely to do much better than the traditional varieties.