How to Hand-Pollinate Plants

If you've been curious about how to hand-pollinate plants and why you might want to, Let's talk about it!

Sometimes referred to as mechanical pollination, this technique may be required in environments where natural pollination does not occur, or where the rate of natural pollination isn't high enough to achieve the desired results.

pink strawberry small organic alexandria alpine not quite ripe yet but close 1 — This Alexandria strawberry was grown indoors, so pollination by hand was a necessity in order to bear fruit

Why Do Plants Need Pollination?

First the basics - why do plants need pollination at all? Let's look at what purpose pollination serves and why it's important in the first place.

Pollination is the process whereby a plant is fertilized and can then reproduce.

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Pollen is the male sex cell in plants, which is produced in the male part of plants - the anthers in their flowers.

This pollen is necessary for fertilizing plants which reproduce sexually.

Do All Plants Need to Be Pollinated?

While many plants need pollination, many do not.

Pollination is the means by which plants reproduce sexually, though many plants also reproduce asexually.

butternut squash flower yellow orange open with bees inside and squash leaves — No need to hand-pollinate this butternut squash, a pair of bees inside have the job covered this time!

Other plants can reproduce sexually or asexually, depending on environmental conditions.

Sexual reproduction via pollination results in increased genetic diversity - important in environments that are variable, in flux, or rapidly changing.

Asexual reproduction results in identical clones of the parent plant (although mutations can still occur). This means almost no genetic diversity. It's a reproduction strategy which works best in stable, unchanging environments.

Some plants will also reproduce sexually when viable, and revert to asexual reproduction as a backup plan. Think about isolated plants without enough surrounding neighbors to be pollinated. Asexual reproduction is a great strategy when pollination is unavailable or not viable.

Why Would You Pollinate Plants By Hand?

jalapenos growing on plant held in hand small dark green peppers — These jalapeños were hand-pollinated because they grew on a porch in an apartment complex, where natural pollinators are scarce.

Lack of Natural Pollinators

Later on we'll discuss indoor and greenhouse environments, which are typically the main reasons for a lack of natural pollinators.

Aside from those areas, though, you might experience a lack of pollinators for several reasons:

Urbanization & Development

in urban environments, or in developed suburbs.

Areas where natural vegetation and native species have been replaced with manicured lawns - and biodiversity is in short supply.

Widespread habitat loss has resulted in reductions in natural pollinator numbers, sometimes to extreme extents, and in pollinator extinction.

Pesticide & Herbicide Use

Pollinator issues are further compounded by rampant pesticide and herbicide use, which can wreak havoc on natural pollinator populations.

Invasive Species

Invasive species can have negative affects on natives, sometimes displacing, overtaking, or decimating the pollinator species which we rely on.

Adverse Weather Conditions

There are a number of weather conditions which will have a negative affect on natural pollination.

Such conditions may require manual pollination in order to achieve complete fertilization and full crop yields.

Some weather conditions to be on the lookout for:

Lack of Wind

Many plants, such as grasses and cereal grains, require wind-pollination rather than insect pollination.

Typically these are plants evolved to grow in large dense stands in naturally windy places, like grasses on the plains and steppe.

If the wind isn't blowing, wind-pollinated plants are not being pollinated.

You can imagine if you decide to grow a small patch of corn in your garden, it might simply not be windy enough for these plants to be pollinated naturally. Hand-pollination offers you the option to step in and help.

Too Much Rain

Rain washes away pollen, and can also prevent wind-pollination in plants which rely on that method.

Rain can also negative affect pollinators, grounding many flying insects who would otherwise be out and about working hard to pollinate everything.

If it's been raining a ton, your pollination levels may be too low and you might consider stepping in to hand-pollinate with any pollen that hasn't been washed away.

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Low Temperatures

Cold weather often limits the activity level and availability of pollinators.

Many pollinators migrate or enter dormancy when the temperature drops, meaning they might not be around to help pollinate your plants.

High Temperatures

As with low temps, high temps can also have an adverse affect on plants ability to pollinate and be pollinated.

Excessive heat often reduces the logevity of flowers, and may reduce pollen viability.

Many pollinators take refuge when hot weather strikes, only coming out again when it's cooled off.

Where I live in the Sonoran Desert, very few insects can be seen out by day during our scorching summers.

It can be eerily quiet at midday on a 117F day (47.2C), and pollination by insects is not usually occurring during the daytime swelter in such hot climates.

Night is a different story entirely, when cool temps coax all the critters out of hiding and the desert comes alive with activity.

On my night hikes and wandering my garden in the dark, I see moths (the primary pollinator in the desert) hitting every flower, ants carrying pollen, bees buzzing (though I don't think most can fly at night), and all manner of insect and critter running around to accomplish their work before the heat of the day returns.

Many flowers in the desert, such as datura, only open their flowers at night to coincide with pollinator activity.

If you're going to be experiencing unseasonably hot temperatures in your garden while plants are flowering, consider pollinating by hand to help increase pollination.

Drought

During droughts, plants can succumb to the lack of moisture and may produce fewer flowers, less nectar, or fail to produce flowers entirely.

If you're expecting drought, saving some male flowers might be a good idea so you can hand-pollinate those flowers which do open.

Hail

Hail doesn't just have the potential to damage plant leaves and stems - it can also wreak havoc on flowers.

A heavy hailstorm can easily wipe out most or all of the flowers on your crops, making pollination impossible.

If you're expecting hail and do not own hail netting, you might consider collecting the stamens of flowers before the hail so that you can then hand-pollinate any surviving flowers afterwards.

Humidity

In the presence of high relative humidity, pollen granules may clump together. This can prevent both pollen transfer and wind pollination.

Pollinating by hand may be helpful during long streaks of high humidity.

Indoor or Greenhouse Growing

If you're growing indoors or in a greenhouse, pollinators are often just not available.

Isolated environments like these are walled off from the ecosystem at large, resulting in very little possibility of pollination happening naturally.

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Pollinating by hand should be assumed to be a necessity in isolated grow environments like these unless you've specifically introduced pollinators.

Wind-pollinated plants can also suffer from underpollination in these environments - so fans and hand-pollination are both great ways to counteract this.

Avoiding Cross-Pollination

In most cases, cross-pollination only has the potential to affect seeds and future generations which we'll discuss in the next section on plant breeding.

There is, however, a phenomenon known as pollen interference whereby cross-pollination with an incompatible species can displace or even block viable pollen. This can reduce crop yields, so there may be some cases where growers intentionally avoid this by isolating flowers and hand-pollinating.

Still a small subset of crops are immediately affected by cross-pollination even before those genes are passed on to the next generation.

This is true of corn, where the kernel size, color, and flavor are all affected by the variety which they are pollinated by.

corn stalks tall organic in desert sand garden few clouds mountains in background — Corn pollen can travel for miles on the wind, and you might not want your neighbor's corn variety to pollinate yours

Many plants with edible seeds like cereal grains and pseudocereals can be adversely affected by cross-pollinating with less desirable varieties, as these genes immediately present in the seeds.

Even if you don't intend to save seeds to regrow, you may still have reason to want to prevent unintentional cross-pollination between certain varieties of crops. If you're in this situation, isolating flowers and pollinating by hand can prevent this problem.

Also consider if you grow for market or sale and are certified organic or non-GMO, unintentional cross-pollination with GM or inorganic plants can immediately result in loss of certification in some cases, so you'll want to be careful to avoid this. Hand-pollination when flowers are isolated ensures that you know exactly what crossed with what.

Intentional Hybridization and Breeding

Intentional hybridization can ensure that cereals and pseudocereals produce the type of grain you want.

If you're a plant breeder looking to create new hybrids, hand-pollination will likely be a key part of that process.

Breeding plants often involves isolating flowers to prevent unintentional crosses, and then carefully pollinating by hand to ensure complete fertilization between the varieties you intend to cross.

Increased Yields

When incomplete pollination occurs, yields can suffer.

If you're expecting reduced levels of natural pollination because of any of the reasons listed above, manual pollination can help to keep your crop cycle on track and increase your yields.