Here we go again. Unfortunately temptation has got the better of me; I am back with bad puns discussing the seedy side of gardening.
This time things are getting fruity. Don't worry I won't be going down the same path as Van Norden in Tropic of Cancer! Understanding plant sex both in terms of pollination and gender is vital to the home gardener.
Fruit bud formation
Before the drama of sex in your orchard can play out you need players: flowers. This is partially based on season and weather but is manipulated in the orchard by pruning. To avoid “castrating” your trees it is worth knowing the parts of your plant that produce the flowers and fruit. Here timing is everything. Basically if flowers and fruit form on new season growth hard pruning is the go. Peaches and nectarines fruit on previous season's growth and once fruited will not fruit again.
Pome fruit like apples and pears fruit on specific lateral buds called spurs. You want to protect these spurs but shorten leafy, vertical growth.
This is not the place for an in-depth discussion on fruit pruning — all I ask is that when pruning your tree have a thought for its sex life and research when, and on what age wood, it flowers and fruits.
Cross pollination
Successful pollination is needed for most plants to set fruit. It is the fertilisation of the embryo and the initiation of seed development that releases hormones that cause the ovary wall to grow into a fruiting body.
Pollination is a natural process but to get a successful crop sometimes the gardener needs to turn matchmaker.
Some fruit varieties are self-fertile so they are easy and ideal for small backyards or balconies where multiple fruit trees are out of the question. Apricots are the prime example of self-fertile fruit. Many other fruits, especially most pome fruit (apples and pears) are self-sterile and need to be pollinated not only by another tree of the same species but one of a different yet compatible variety. This is really nature's way of ensuring a diverse gene pool.
As orchardists we are interested in fruit for particular purposes and to maintain the qualities of taste and size we have propagated them asexually through grafting or cuttings. Still, to get fruit, we must go along with the predilections of our trees and it is something to get right early on in establishing your fruit collection. You can get quite confused about what variety goes with what.
This is all simplified as fruit trees are usually classified in groups to easily assess compatibility. The Diggers website lists suitable mates for all the fruits that we sell requiring cross pollination or you can go along with a heritage collection that takes away all the guesswork. Jonathan is easy and a fairly good pick, being compatible with many other apples.
Chromosome threesome
Ploidy refers to the number of chromosomes found in the cells of all living things. The common number is 2 (diploid), one from the father and one from the mother, just like people. Things are never so straightforward in the plant world and some have 3 chromosomes (triploid).
The home orchardist will encounter triploids most commonly in apples. Triploids produce essentially sterile pollen, they cannot fertilise themselves or others. This means they need a compatible pollinator. The tricky part is that in order for the pollinator tree to set fruit it must either be self-fertile or else you will need another compatible variety to act as the “pollinator's pollinator.” Triploid apples like the iconic Bramley's Seedling more than make up for their complicated sexual needs as they are usually vigorous pest resistant trees that produce heavy crops of large apples.
Banana cultivars are the other great triploid fruits. They fruit without fertilisation with only little black specks in place of seed. The large seeded original banana species fruit is almost inedible; like eating a mouth full of broken teeth! The danger for the banana industry is that without the diversity created through sexual reproduction and almost total reliance on one variety, Cavendish, they are vulnerable to complete wipe-out from disease.
Avocado Arthur and Martha
Probably the most common question of a sexual nature I get in the garden involves the cross pollination of avocados. Avocados have “perfect” or “bisexual” flowers; they have both male and female parts. The intriguing thing about avocados is that over two days they open first as female then the next day as male. We group avocados into types A & B.
Type A are female and ready to be pollinated in the morning and male and releasing pollen the following afternoon. Type B are ladies of the afternoon arising the next morning as males to release their pollen.
Ideally, to help boy meet girl, grow a type A avocado with a type B to get a bumper crop. In reality for the backyard you don't need to stress too much about having one of each particularly if you have a type A variety.
Nature doesn't run like clockwork and flowers sleep in or stay up late and there are actually moments on a tree when there are at least some male and females open at any one time. Fruit can even occasionally form without pollination producing seedless “cocktail” avocados.
Sexism in the garden
As gardeners we can sway the balance of male and female plants in our landscape with unforeseen consequences.
While they orchardist craves the fruitful female, in the ornamental garden fruits can cause mess and unwanted seedlings. Horticulturist Tom Orgen, in his book Safe Sex in the Garden, documents urban foresters’ preference for male street trees. Male clones produce none of those pesky fruits and seeds that litter roadways.
So it makes sense to grow tidy male clones. However, what males do produce is large amounts of pollen. Orgen argues our “sexism” produces high allergy landscapes.
This pollen cloud, that is pretty evident in most treed streetscapes, countermands the concept of trees as air filters. In some instances they are the wheezy lungs of the city. Hopefully we can return some balance to our cities by letting some of those messy ladies back into the city: a good reason to use robust and diverse seed grown trees.
Sisters are doing it for themselves
While the patriarchy is holding sway over our street trees, the sisterhood fights back with the babaco. Babaco is a natural papaya hybrid that like botanical amazons produces only female flowers. It is literally “virgin fruit” or parthenocarpic. This is a great advantage over its ancestor the mountain papaya that requires the space for a non-fruiting male plant to produce a crop.
More beetles and the bees than the birds and the bees
Spare a thought for the beetles and bees that are the intermediaries in these fruity flings. Sure, they get paid in nectar and pollen for their services but they need a place to live and supplementary food. A diverse orchard should incorporate flowers that make your backyard a magnet for pollinators — think of growing a mini meadow rather than monoculture lawn. Meadows and “timber insect hotels” also promote the local bees like the magnificent blue banded bee that is our version of the bumblebee, a great “buzz pollinator”.
Although a great excuse for some bad puns, looking at plants as driven by sex makes us better gardeners. When we prune think of flowers, when we plant think of their sex companions; it all leads to backyard bounty.