As with melons, cucumbers and watermelons, squash are monoicious plants : male and female flowers are to be found on the same plant. The male flowers are easily recognisable because they are to be found above the foliage on long stems. The female flowers are also easily recognisable because at their base is to be found the future fruit, the ovary, which already with have a well defined shape. The size of the ovary can be of some consequence : in the variety dAlbenga for example it can reach 15 cm in length.
Once the female flower is fertilised the fruit will develop. If the flower is not fertilised the fruit will wither and die.
On the squash plant the male flowers will appear well before the female flowers and also in far greater numbers. It is also noticable that in periods of hot weather the male flowers are far more numerous.
The male flowers possess both pollen and nectar, the female flowers only nectar.
They are very short lived : they will open up before dawn and will close completely by mid-morning.
The squash can be self-pollinated: a female flower can be fertilised by pollen coming from a male flower of the same plant.
However, cross-pollinations are predominant: a female flower is fertilised by pollen coming from different plants of the same variety or of a different variety within the same species.
The insects are the vectors of these cross-pollinations. To ensure the varietal purity, a distance of 1 kilometre is needed between 2 varieties of squashes.
It is essential to understand that cross-fertilisations can only take place between varieties of the same species. There can be no cross-fertilisation, and therefore natural hybridisation, between different species of cucurbita, save for the remote possibility with the species Cucurbita argyrosperma.
Actually, American botanists have remarked that Cucurbita argyrosperma is characterised by different levels of compatibility and so there is potential for cross fertilisation:
- The greatest degree of compatibility is with Cucurbita moschata.
- A lesser degree of compatibility is apparent with wild populations of Cucurbita pepo as well as with a few varieties of Cucurbita maxima and some forms of Cucurbita foetid issima.
- There is an even lesser possibility of cross-fertilisation with other wild populations such as Cucurbita lundelliana, Cucurbita martinezii, Cucurbita pedatifolia, Cucurbita digitata.
To sum up, therefore, before all else, hybridisation is between varieties of the same species. There is no cross-fertilisation between Cucurbita pepo, Cucurbita maxima, Cucurbita moschata and Cucurbita ficifolia. The only other species capable of hybridisation with the first three of these four is Cucurbita argyrosperma. It should be stressed, however, that Cucurbita argyrosperma is little known and rarely cultivated in gardens in temperate zones.
So the gardener can produce his own squash seeds in his own garden ( provided that his garden is sufficiently isolated from any other garden producing squashes) if he grows only one variety of each species: for example, a courgette (Cucurbita pepo), a hubbard (Cucurbita maxima),a butternut (Cucurbita moschata) and a Siam squash (Cucurbita ficifolia).
If you wish to produce your own seed you would be well advised not to grow a variety of Cucurbita argyrosperma near to any variety of Cucurbita pepo, Cucurbita maxima or Cucurbita moschata. On the other hand you could quite happily grow one variety of Cucurbita argyrosperma and one variety of Cucurbita ficifolia in the same garden as there would be no danger of cross fertilisation.
The gardener cannot, at least in open pollination, produce the seed of a variety of green cougette if there is in the same garden any other variety of Cucurbita pepo, for example a yellow courgette.
Actually, the bees will cross fertilise these two varieties of Cucurbita pepo and the hybridisation will only become apparent in the second year when the seeds of this cross-fertilisation come into production.
It is important to understand that the hybridisation takes place in the true fruit which is in fact the seed. What we eat is the flesh of the false fruit which is actually the enlarged ovary. The ovules have been fertilised by the pollen transmitted from the male to the female flower. Each fertilised ovule becomes a seed.
When the ovule of one variety is fertilised by the pollen coming from another variety (of the same species) it creates a seed whose characteristics will be very different.
We shall now describe the techniques of controlled fertilisation which will permit the gardener to produce seed from more than one variety of the same species in the same garden without resorting to the usual distances of isolation.
The first method is quite simply to cultivate different varieties each protected by a veiled cage. Thus you can make a mini-tunnel covered with mosquito net or fleece or a fine meshed metal. The only real requirement of this method is to ensure the introduction of pollinating insects into the mini tunnel because without them there will be no fertilisation.
Bumble bee hives are sold by certain specialist companies but they obviously represent a certain cost. This cost can however be shared between two or three gardeners because the mini tunnels need only be visited by the pollinators every two or three days. The bumble bees go back into the hives at night and so, can easily be transported between gardens.
One can also get the optimum use from such a hive (which normally would be destined to pollinate large areas over a period of weeks) by creating a fairly long tunnel containing one variety of each species of cucurbita, with one variety of cucumber, one of melon, one of watermelon, one variety of aubergine and one of okra. All the seeds thus produced will be pure.
The second technique of controlled fertilisation is to do it manually. With this method you must tie up the male and female flowers which are at the point of opening up the next day. With a little experience you will soon learn to identify them because they acquire a characteristic shade of yellow. Sometimes the tip of the flowers of certain varieties will be very slightly opened the evening before their flowering. The ligature should be placed at the extremity of the flower. We quite simply use masking tape for this job. You should seal at least two male flowers for each female flower sealed.
In gardens with a very large number of squash plants, it is wise to mark the sealed female flowers by indicating the plant with a coloured stick, or with a piece of coloured tape stuck on the leaf above the flower or any other marker that will enable you easily to find the plant the following morning.
It is also wise to follow the same path the following morning and in the same direction, for example east to west . Actually, it will be much easier to undo the ligatures on the flowers if you come at it from the same direction especially because of the lie of the leaves.
In the morning, the male flowers are harvested, the ligature undone and the petals removed. The tape on the female flower is then carefully removed. If one or other of the flowers, once the tape is removed, fails totally and naturally to open out, this indicates that that particular flower is not yet mature and it cannot then be used for the process of manual pollination.
The pollination is effected by dusting the pollen of the male flower on all parts of the stigmata of the female flower. You must be very alert because it is entirely possible for a bee to land on the female flower whilst you are carrying out this process. If that were to happen, you would have to abandon that particular female flower because it could have been contaminated by pollen from another variety of the same species.
When the pollination has been correctly carried out, you must then carefully reseal the female flower with tape. You must not forget then to carefully mark the pollinated fruit by attaching some horticultural tape to the peduncle of the pollinated flower so as to easily recognise at the end of the season the fruits that have been manually pollinated. The tape must be sufficiently loose to allow the fruit to grow naturally.
You would be well advised to carry out this exercise as early as possible in the day. In fact, pollination carried out at the end of the morning during warm weather has very little chance of success because the pollen will have heated up and fermented and will no longer be viable. Dont forget that if the female flowers are left to their own devices they will close up by the middle of the morning, around 10 oclock.
Before carrying out the manual pollination you should inspect the base of the taped female flower to ensure that it has not been entered : it can happen that certain insects, such as large bumble bees, force a way into the flower. This can also happen after the manual pollination and so it would be wise to inspect the flowers that have been pollinated by hand the following day to ensure that they have preserved their integrity. This kind of intrusion remains, however, very much the exception.
As far as is possible, avoid using a male flower from the same plant as the female flower.
Manual pollination will more readily be crowned with success if it is carried out at the beginning of the plants fruiting. Where a fruit has already formed on a plant (as the result of a natural fertilisation) that is destined for manual pollination, you are strongly advised to remove it so that the manually pollinated fruit should benefit from the full vigour of the plant. Also the number of fruits pollinated per plant depends very much on their normal season of growth, upon the climate of the season and according to the characteristics of the variety concerned.
Thus you can pollinate one fruit only on a giant pumpkin, two on a potimarron type, three on a pattypan and up to a dozen on a variety such as Golden Apple.
We have noted that certain varieties of squash have proved more recalcitrant than others to manual pollination. This is the case, for example, with the variety Green Olive. It remains to be proved, however, whether this is an intrinsic feature of the variety as such or whether it is the result of some environmental problem.
When at the start of the season you have the intention to carry out manual pollination, you should have close regard to the spacing of the plants to ensure that the stems of different plants do not mix and to ensure that the flowers, especially the male flowers, can easily be identified from one plant to another.
In order to profit from a good genetic diversity it is necessary to grow at least 6 plants of a variety. The ideal is to grow a dozen or better still 20 if garden space allows.
After harvest, it is recommended to wait as long as possible before opening up the fruits and harvesting the seed. The seeds, in fact, continue to mature inside the fruits : if one waits a month or more before opening the fruits, the quality and viability of the seed is very much improved.
When the fruits are opened, the seeds are extracted by hand and washed thus removing the pulp. They are subsequently placed to dry on a small tray in a dry, well ventilated place. Squash seed takes several days fully to dry. A fan can greatly speed up the process. The seeds are totally dry when they split upon bending. You are strongly advised against drying them on paper because they will become stuck to it.
Squash seeds have a viable life of six years. They can, however, remain viable for up to ten in the right conditions. The different varieties of Cucurbita pepo contain, per kilo, between 5000 and 20000 seeds.
The different varieties of Cucurbita maxima contain, per kilo, between 2500 and 5500 seeds.
The different varieties of Cucurbita moschata contain, per kilo, between 5200 and 12000 seeds.
Although squash are fundamentally allogamous, they are able to self-pollinate. Certain American authors put forward different reasons for this. The first is the fairly drawn out development of the Cucurbita which allows for the pollination of the female flowers by male flowers of the same plant. The second is the very common practice amongst the Ameridian peoples to mix in the same garden plants of maize, squash and haricot beans, thus forming a barrier between plants of the same variety.
Whatever the reason, the ability to self-pollinate has been regularly used by seedsmen to create new varieties and it would seem that Cucurbita are not too prone to what we call genetic depression.
As a result, it is very easy for a gardener to play at creating his own varieties by crossing two varieties of the same species. The technique is similar to that employed in manual fertilisation with the exception that the male flowers are collected from a different variety, but of the same species.
Thus, for example, the evening before one could tape the female flowers of Golden Delicious (in the form of a heart) and the male flowers of Marina di Chioggia (which are both Cucurbita maxima). The following morning the pollination is carried out as already described. For sure you must not forget to attach a label naming the variety of female and of the male. The seeds are harvested in autumn and then sown the following season.
When the cross pollination has been carried out between varieties that are very pure (which is often the case with those grown professionally) it will create plants in the first generation which are relatively similar and so it is not necessary to grow a large number.
This is not the case, however, where the varieties used for the cross pollination are amateur varieties with relatively variable characteristics. The cross pollination will here create plants of the first generation that are fairly diverse and so in this case you can grow a greater number of plants than in the former case.
You are going, systematically, to self-pollinate the plants of this first generation That is to say, the female flowers of each plant will be manually pollinated by male flowers of the same plant. The gardener will select fruits according to his desired criteria, for example the choice of a bronze coloured, warty skinned heart shape. He will only harvest the seeds of those fruits he desires.
These seeds are then sown in the following year and all the plants self-pollinated. The gardener will then again select only the fruits in the form chosen, namely bronze coloured, warty skin in the shape of a heart. This process is repeated for a number of years until the plants produce just those characteristics chosen in the first generation.
The variety is thus said to be stabilised. It is, however, highly likely that, from time to time, fruits will appear which are not true to type as a result of recessive genes.
A new variety can also be created where for example one finds growing in the garden a squash that does not correspond to the variety planted. One can call this a mutation or perhaps more poetically a gift of the angels.
If the gardener likes the colour, or the shape, the flavour or the earliness of this mutation he can use it as the basis of the process of auto-pollination in order to obtain, after a number of years, a stabilised variety giving only fruits similar to that originally discovered in the garden.