Late Season Nectar for Beneficial Insects

In central MA, we veggie gardeners have been blessed with an extended growing season this year, with temperatures dipping below the 40′s only for the first time last week. This means I harvested ‘Cherry Bomb’ hot peppers and green bell peppers right into October – the latest ever in memory. This is good news for my household (frozen fresh, we’ll be enjoying our abundant harvest in burritos, chili and shepherd’s pie well into the winter!) but GREAT news for pollinators and other beneficial insects visiting the red, orange and yellow marigolds (Tagetes tenuifolia) that edge our vegetable beds:

Hot peppers still going strong on October 6th, along with annual marigolds (Tagetes)

When I sat on this wall with a cup of tea the other morning, these marigolds were being mobbed by no fewer than 10 bumble bees of varying sizes, a metallic green sweat bee, a large blue wasp, a parasitic tachinid fly and several sizes of hoverfly (flower flies). These insects are all plant pollinators, but many are also important garden predators, preying upon vegetable pests such as caterpillars and aphids. The insects were completely oblivious to my presence as they searched out sweet nectar…meaning I wasn’t worried about being stung. The bumble bees won’t sting unless you harass them (or their nest). The sweat bee may land on your arm to lap at the salty perspiration, but if you hold still, he’ll soon fly away. The blue wasp is a solitary nester, which means they have no communal hive to defend (unlike honey bees), and won’t sting unless you threaten them. The hover flies don’t sting at all:

The larvae (juvenile form) of hover flies are important controllers of soft-bodied insect pests such as aphids. Robert Sousa photo

If you grow vegetables, a variety of flowering plants in and around your crops are essential to encouraging these beneficial insects that patrol for pests. Marigolds are easy to grow annuals, but they bloom their heads off right through summer and fall until the first killing frost. This means they support late-season generations of beneficial insects even longer than most of the crops they help protect:

In these beds, the greens, spinach and melons are gone by, and the soil already mulched for winter with 6" of farm compost. Yet still the marigolds hold on...

We like to plant the single-flowering type of marigold around our veggie beds, because their simple flower shape make it easy for pollinators to access the nectar at the flower’s center:

If you zoom in on this single form of marigold flower, you'll see at least two tiny pollinators slurping up nectar at the flower's center..

Double forms of flowers make it harder for pollinators to reach the nectar inside. These  double marigold flowers are packed with dense, ruffled petals that make it difficult for all but the largest pollinators to force their way into the nectar store:

Double flowers - not as user-friendly for pollinators!

Despite worldwide declines in many pollinator species (including honey bees and some bumble bees), it’s clear that at least in my little corner of the world, pollinators can still exist where habitat exists for them. The late-season nectar makes it possible for many of the “beneficials” to squeeze in one last generation before dying off or hibernating. Compared to last year, when drought and early frost wiped out most pollinator habitat in September (in central MA), one final generation this year puts populations in in a better position to withstand whatever weather weirdness we experience in 2012.

Although annuals such as marigolds are long blooming, easy to grow and readily available anywhere plants are sold, don’t forget to plant some native late-season bloomers that continue to bloom after frost hits. Frost-hardy perennials such as New England aster and white snakeroot (Ageratina altissima, formerly known as Eupatorium rugosum) are still in their full glory here in New England – their flowers are also crowded with pollinators:

Remember that even with nectar plants to fuel them, beneficial insects also need nesting sites to complete their life cycles and survive from year to year. Leave an area of undisturbed ground near your vegetable beds, as nesting sites for solitary bees that excavate tiny tunnels in the soil to build their nest. Don’t till this area in the spring, to avoid destroying overwintering nests. If you don’t have much room, or lack old trees where many beneficials like to nest, a bee box can also supply pollinators with nesting opportunities:

A well-used solitary bee nesting box. Drill holes of several sizes, but do not drill all the way through the wood. Many wood nesters won't nest in a tunnel open at both ends.

A piece of untreated wood drilled with varying size holes will accommodate a range of beneficial insect nests, including orchard mason bees, who lay their eggs in the tubes, sealing the end off with mud to protect cocoons through the winter. If you have spring-blooming fruit trees, you’ll want to have these efficient pollinators in large numbers! Bumble bees often construct their nests underground in old mouse holes, but they will also use a box like this one at Garden in the Woods in Framingham, MA:

This box is highly visible and off the ground, so garden visitors are unlikely to step on the nest and risk being stung.

What do you have growing in your gardens to support late season pollinators? And if you grow vegetables, please share your success stories of attracting natural pest controllers to your gardens!

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