When one thinks of kitchen gardens, vegetable plots and allotments one rarely visualizes a scene replete with masses of flowers. No our imagination and memory play us pictures of rows of worthy vegetables; a patchwork of foliage with few if any flowers. And if you trawl the associated books flowers rarely get a mention except in the older tomes where a row of flowers may be included 'for cutting'. So why do we so ruthlessly exclude all the flowers from our visions? Especially as they are such an essential part of most plant's lives, a joy to behold and can be so useful to us in so many ways.
There have often been rather optimistic designs for 'cottage gardens' incorporating edible crops in amongst flowering plants. It's a lovely dream fabricated, temporarily, at garden shows. Sadly in practice at home the cottage garden theme has never worked well as the crops need much better conditions than they can get amongst so many competitive neighbours. Furthermore the tending and harvesting of such mixed cropping is difficult and the crops 'attractive' seasons rather short. On the other hand the alternative of making our vegetable patch more floriferous can offer us many benefits. In fact with some crops it already is floriferous but we rarely take much notice of their blooms.
Flowers for crops- other than for our fruits flowering is not essential for many of our crops and indeed for some it is a disaster if the blooms appear. All the root crops, most brassicas, alliums and salad leaf vegetables are grown for their immature non-flowering parts and if they flower, or bolt as we call it, they become effectively unusable. Our struggle is to get these crops to grow unnaturally large and succulent without bolting.(-though once the crop has gone to waste then if the space is not needed their flowers can be left to benefit the garden ecology.) In the case of potatoes the flowers appear at the same time as the new tubers are initiated and if the flowers are allowed to set and form seed-pods this can reduce the tuber harvest by about 5-10% so it is worth removing them! However many of our most important crops depend on their flowering to successfully complete their cycle; such as sweet corn, all the peas and beans, pumpkins, cucumbers & squashes, tomatoes and the other fruit like vegetables. Not all these flowers are small and insignificant; for example remember the pumpkin family blooms reach hand size. There are even some highly coloured flowers available in some vegetables such as the wide range of beans from white and cream to reds and purples. The start of flowering of the vegetables we want to flower is said to be the best time to give one really good watering which will then, allegedly, double the crop. (-probably not so true on the western side of the UK)
Flowers as crops- apparently we eat very few flowers but as tastes are becoming wider then it is surprising how many petals if not whole flowers are slowly being added to our fare. I regularly add pot marigold, rose and nasturtium petals to many dishes, use the flowers of rosemary, thyme, sage, hyssop, lavender, sweet Cicely, violets, pansies and borage in others, chomp on day lily flowers whenever I'm in their vicinity and make a demon liqueur from primroses and cowslips. I suppose you can count globe artichokes as it is their flower buds if not the flowers as such that we eat. (Several other flower 'buds' have been eaten in a similar way; immature sunflowers I find just edible, though several of the thistle family such as Silybum marianum are suggested I have never found them either palatable or even easy to nibble.) Our major flower feast is the broccoli's and cauliflowers which are masses of immature flower buds arrested at a gross stage of development. It is the high degree of development and breeding that makes these so tricky to grow well -they so want to bolt and bloom. (Capers and cloves are also flower buds but a bit beyond the average UK garden!)
Flowers as attractive companions- one of the best of reasons for introducing more flowers into the kitchen garden is for their benefits to pollinating and predatory insects. Almost all flowers are useful in some way though man made 'doubles' are often less value having given up their pollen or nectar bearing parts to make more petals. Early flowering blooms are most useful as they help get the insect population to come in and then increase quickly at the start of the year and this is particularly important if you grow early flowering fruits such as plums or peaches. An under planting or orchard border of flowering redcurrants and spring bulbs is especially useful for encouraging bumble and humble bees for just such a purpose. Many flowering plants are worth growing just because they are so effective at bringing in and maintaining insect populations; the poached egg plant Limnanthes douglasii is particularly good and widely used. The beautiful ferny leafed blue flowered Phacelia tanacetifolia is also frequently grown, (particularly by sweet corn farmers!) as is Buckwheat Fagopyrum esculentum. I find the alpine strawberry to be useful as it has such a long flowering period and the fruits are also handy. Most beneficial flowers for later in the year are the various brambles and then finally ivy which feeds up the insects ready for hibernation. I notice the winter flowering honeysuckle Lonicera fragrantissima is heavily visited, especially by honey bees, on warm winter days and is well worth including where space is available. The winter blooming hellebores though poisonous are also valuable in an orchard or fruit cage just for their rain proof flowers which are rich in pollen.
Flowers as repellent companions- many flowers deserve space in the vegetable plot because of their perfume, but not for our benefit. As with the scents of aromatic herbs flower perfumes fill the air and thus confuse pests searching for their lunch by smell, which most pests must do. Any flower with a perfume can thus mask a fainter scent. Say for example that of carrot foliage, this will then make it harder for the carrot root fly to find it's quarry. So although flowers may not eliminate all the damage at least they might reduce the extent. Also some blooms may act as sacrifices attracting pests away from crops; e.g. flowering umbelliferae family members may attract carrot root fly away from their main targets. Some smells may even actually repel pests away as with the pungent scent of all parts of the French marigold family and that of the edible chrysanthemum Shungi-ku.
Flowers for fertility- Although at first glance there may seem little potential here, after all it is other organisms on the roots of plants that mostly fix nitrogen. However small things may add up; certainly growing more flowers will bring in and support more insects thus more insect droppings and dead bodies will drop onto our soil. More insects will bring in more birds thus more feathers and droppings will be deposited in our garden. And although their mass is small when considered to the foliage, roots and haulm of a green manure none-the-less the rain of falling petals does add to the soil organic matter content. Also only a few flowers are closely related to vegetable crops so most can be fitted into a vegetable garden with little concern as to their rotation. (Take care-Stocks and wallflowers are related to brassicas, and stocks, and nasturtiums, even get the same caterpillars in bad years) If large quantities of flowers are grown, as for cutting, then they can form an extra year for a rotation giving additional benefits as a break crop. (I find especially valuable as a green manure/liquid feed break crop is borage, it is actually the leaf rather than the flower that is most useful as it has a very high nitrogen content and rots to improve the soil or make a rich, rather glutinous, feed.)
Flowers for cutting- and finally of course are those flowers that we want for the house. It makes sense to grow flowers for cutting in the vegetable area as there their blooms can be taken without spoiling the overall appearance of the ornamental areas. And some such as sweet peas really need the intensive care, and regular cutting, only really available in with the vegetables. However rather sadly there seem to be fewer flowers for cutting in most gardens and allotments I now visit and I guess their popularity has passed. Yet when I compute the relative value of growing flowers to vegetables then cut flowers win hands down! Just look at the price of flowers compared to veg! So if you buy many cut blooms or would like more to enhance your home then consider putting carnations, pinks, stocks, wallflowers, sweet peas, dahlias, chrysanthemums, gladioli or whatever you fancy in alongside your turnips and potatoes. They could be your most valuable crop for all the reasons above, and in hard cash terms too.