Growing fruit trees in pots is tough… and growing potted subtropical fruit trees indoors is even tougher. The entire indoor growing environment is alien to a fruit tree native to any climate, but for warm-weather trees trying to survive and produce fruit in cold northern winters? Ouch!
Fortunately, there are some easy tips and tricks to help your potted trees produce fruit. If you’ve ever considered growing pomegranate trees on your windowsill but weren’t sure how to ensure a potted pomegranate tree’s blossoms are pollinated and will produce fruit, this is the article for you!
NOTE: This post contains excerpts from my book, The Complete Mini-Guide to Growing Windowsill Pomegranate Trees: A Reference Manual for Northern-Zone Gardeners. The book is a comprehensive instruction manual for growing potted pomegranate trees indoors, and may be purchased on Amazon in ebook or paperback formats for less than the price of a fancy cup of coffee!
Pollination Basics for Pomegranates (whether the tree is grown indoors or out!)
Don’t be disappointed if a new pomegranate plant doesn’t start blossoming within its first year. The plant is not an aggressive grower, and works its way towards maturity at its own leisurely pace. You may get a few fruits in the second year, but if you don’t harvest any until year three, that’s not unusual. The pomegranate is self-pollinating, but the addition of a second plant of a different cultivar will tend to increase fruit set. Flowers may appear singly or in clusters of up to five, and are produced on the tips of the brittle branches.
Blossoms tend to appear on new growth sprouting from two- to three-year-old branches. Blossoms appear in colors along the red spectrum; white, yellow, orange and red. You may get extra-ruffled, double-blossom flowers, which are typical of some of the more ornamental trees; if you see many of these on your tree, beware! The fruit set from double-blossomed varieties is notoriously sporadic or nonexistent.
The trees tend to produce two types of flowers. Male flowers will drop off after the blossoms fade, while the fruit-bearing blossoms will develop into juicy pomegranates with just a tiny calyx as the remnant of the flower it used to be. The male flowers are often described as bell-shaped, but you can easily distinguish them from the fruit-bearing blossoms by their shape. Male blossoms look like the standard, petal-based flower, while the fruit-bearing blossoms have a little round baby fruit at the base – so small that you might miss it if you weren’t specifically looking. That little knobbly end of the fruit-bearing blossoms gives the flower a shape like a peanut, with an initial swell of the potential fruit and then a slight narrowing before the swell of the petals.
When to Assist Pollinating Potted Pomegranate Trees
The pomegranate’s pollination needs are simple… and yet results are complicated. A healthy, established tree will tend to start blossoming in early spring, and as old blossoms fade, new ones should continue to be produced throughout the year. Under natural circumstances, pollinators such as bees and hummingbirds (hummingbirds ADORE the pomegranate, and hang out on my deck all summer visiting the lovely orangey-red flowers) will do all the work of pollination, and the blossoms will produce fruit. The blossoms that opened earliest in the year will produce the largest, best-quality fruit; blossoms that opened later in the summer and early fall may not reach maturity before cold weather sets in, and if they do, the size and quality tends to be lower.
On the surface, this pollination process all sounds very simple and straightforward. The tree knows when to blossom, the birds and the bees transfer the pollen, and you end up with fruit without having to lift a finger…
…but for a windowsill-grown pomegranate, things aren’t quite so simple. If you are interested in harvesting fruit from your potted pomegranate tree, there are going to be times when you will need to pollinate the tree yourself, either to increase the size of the harvest and sometimes to encourage any fruiting at all.
Most obviously, if your tree begins to blossom indoors instead of on your patio, those blossoms are quarantined from their natural pollinators. If the bees can’t get to the flowers, you need a substitute method to transfer pollen!
Secondly, even if you have your tree outdoors for the entirety of the growing season, you may not be able to attract pollinators at the level the tree is used to in its natural environment. This will depend on the ecological life of your general location, as well as the attractants of your specific yard & garden. There are a thousand little factors that can affect your pollination landscape; do you or your neighbor keep bees? Do you grow diverse, thriving gardens that attract hummingbirds, or is your one plant pot competing with the greenhouse two miles up the road? Does your tourist-trap neighboring attraction constantly spray pesticides that kill off the bee population?
You can analyze your hummingbird populations and assess the bee activity and scrutinize your neighbors’ spraying practices to try to figure out your best course of action… or you can just decide it’s better to be safe rather than sorry, and roll up your sleeves to play pollinator yourself. Whether your tree blossoms indoors or outdoors doesn’t change the fact that assisting in pollination is almost always beneficial to the fruit load and quality – and you don’t have to worry that you are stealing the bees’ lunch! If you lend a hand by transferring pollen, the nectar is still there, and all you’ve done is help the tree without hurting the pollinators.
It’s true that an outdoor-grown tree will tend to produce some fruit even with limited pollination, so you could just skip the process and hope for the best. However, it’s been extensively studied (pomegranates are an important cash crop in some parts of the world, after all), and results strongly indicate that poor pollination is directly associated with low fruit yields, and the fruit that is produced is of poor quality.
If you want to get into the nitty gritty specifics, consider the interior of the fruit. Each of those juicy arils represents a distinct pollination instance. If you are relying on a quick fly-by from one lost little bee on his way to greener pastures, those blossoms aren’t going to get the quality attention they need to produce those seeds. You may get fruit, but it will be small and even misshapen because there isn’t enough viable arils in the fruit to plump out the rind.
How to Assist in Pollination
Pollinating the blossoms is quick and easy, but there are a few tricks you can use to make your fruit yield and quality even higher.
Perhaps most importantly for the windowsill grower, keep an eye on which flowers you are using to pollinate. Any single fruit-bearing blossom already contains enough pollen within itself to successfully set fruit, so technically you can just shake the tree and call it good. However, studies have shown that there is better fruiting results if you transfer pollen from male flowers to the fruit-bearing blossoms. This isn’t critically important, but for the indoor gardener where every fruit is a victory, it helps to know any shortcuts to success.
Additionally, it’s important to get those blossoms pollinated as early as possible. Although fertile for several days after opening, the yield for blossoms that were pollinated on the first day they open is far higher than late-pollinated flowers. The size is also far larger if you can get to the blossoms on day one, so don’t wait!
Finally, transferring between trees is helpful when possible. Although self-pollinating, the pomegranate has been proven in multiple studies to benefit from cross-pollination from other varieties. If you have no other pomegranate trees (or if the blossoms don’t open at the same time), that’s just fine – your tree is completely capable of producing, and producing well! However, if you have the option, always intermingle pollen from multiple trees when you move from blossom to blossom.
To pollinate the blossoms yourself, you can use any small tool capable of transferring the tiny grains of pollen. Many people recommend a q-tip, but in my experience this tends to just collect and hoard the pollen, rather than move it around, so I prefer to use a paintbrush or even the tip of my finger. Using your tool, whatever that tool may be, your goal is to “dust” the grains of pollen from flower to flower. Your touch should be very light so you don’t damage important flower structures, so be gentle!
Since the male flowers don’t produce fruit anyway, you don’t have to feel guilty for using the cheater’s method: when I’m in a rush, I just pluck off a single blossom and rub it’s face with the fruit-bearing blossoms on the tree. You won’t find many official or commercial resources recommending this method, but although it’s not pretty, it works just fine for me!
Interested in reading more about how to grow potted pomegranate trees on your windowsill? Check out my other articles: Growing Windowsill Pomegranates: 3 Cultivars