Pollination of Vegetable Crops in a Warming Climate

Pollination is the movement of pollen from male to female flower parts of sexually reproducing plants. It is often accomplished by wind and insects and results in the development of some type of fruit containing seeds for the species’ continuation. Farmers and gardeners in the mid-Atlantic are finding that high day and evening temperatures can cause vegetable plants to drop flowers and small fruits or produce deformed and under-sized fruits. This  problem has been observed in crops like bean, tomato, and pepper (mostly self-fertile; individual flowers can pollinate themselves), and in crops like squash and pumpkin (require cross-pollination between flowers).

How do high temperatures affect pollination?

All fruiting plants have an optimal temperature range for the pollination/fertilization process. High temperatures can reduce pollen production, prevent anthers from releasing pollen, kill pollen outright, and interfere with the pollen tubes that serve as conduits for uniting sperm cells and eggs (fertilization) inside undeveloped seeds (ovules). High temperatures can even injure flowers before they open. Night temperatures are increasing at a faster rate than day temperatures as a result of climate change, and seem to be most responsible for these pollination problems.

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Comfy plant places and new garden spaces for vegetables

Every time we plant a seed or baby plant in our vegetable garden we are hoping for the best outcome- a healthy crop and big harvest. Gardening success comes from learning about the needs of our crops and doing all we can to meet those needs. Climate change is causing us to think a little more deeply and holistically about those plant needs and our gardening practices.

In addition to making sure that plants have enough space, water, and healthy soil, we can alter how and where we plant our crops (“comfy places”) to help them adapt to increasing summer temperatures. We can also consider ways to expand or shift our food garden spots (“new spaces”) to better manage growing conditions and produce more food.

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Fighting CO2 on a Balcony

It’s well known that atmospheric carbon dioxide (CO2) is one of the leading causes of climate change and that plants play a role in mitigating its impact by taking in carbon dioxide and releasing oxygen. But did you know that even the smallest gardens can make a difference? Container gardens can be effective ways for adding plants to the ecosystem, nurturing pollinators and other beneficial insects, and even providing food for your table.

A container garden with mixed perennials and annuals provides beauty, food, and habitat. Photo: Pat Wilson

High above Columbia’s Wilde Lake at the Residences at Vantage Point, long-time gardener Barbara Schuyler continues the gardening that was her passion when she and her wife Pat Wilson lived on a rural property. More than 90 containers of shrubs, annuals, perennials, and vegetables grace two balconies that face west and south.

Barbara’s approach to container gardening

Shrubs and perennials comprise a significant part of the garden. Hardy perennials winter over and are especially effective at drawing down carbon dioxide. Some of the perennials, like the orange butterfly milkweed (Asclepias tuberosa) pictured below, are natives. Native plants are well-suited to our climate, require less care than imported species, and support native insects. Barbara’s native plants also include lots of Rudbeckia, some Echinacea, and several Heuchera

orange and blue flowers planted in a container garden
Native butterfly milkweed (orange flowers) combines beautifully with the blue-theme flowers. Photo: Barbara Schuyler

In addition, each year Barbara and Pat decide on a theme and collect annual seeds to plant when the temperature warms up each spring. Last year, the blue flower theme provided a consistent backdrop for the foliage and flowers of other plants.

She uses regular potting soil and each spring spreads the old soil on a tarp to remove roots and debris and returns it to the pots with a portion of fresh potting soil added.

Her collection of containers is eclectic and includes salad tables for vegetables, wine barrels, ceramic and plastic pots. A container exchange in the building helps many patio gardeners find pots that meet specific size and decorative needs. Reusing and sharing materials can help reduce CO2 associated with buying and shipping new products. She also tried felt bags but was not pleased with the results.

spray handle attached to kitchen sink
Photo: Christine Hipple

Watering 90 containers with a watering can during dry spells would be a major challenge, so Barbara purchased a garden hose sink adapter to allow her to connect a lightweight flexible hose to the kitchen sink.  

One big advantage of balcony gardens is that deer can’t get to them, though she has seen a squirrel or two.

Benefits

Visiting her garden every morning is a joy in itself. It provides Barbara the opportunity to be present with her plants, be aware of their needs, and appreciate what they offer throughout the seasons.

Even at this extreme height, pollinators are attracted to and supported by the garden. Three species of bees, several types of moths, and even a few monarchs have been spotted.

Lettuce and arugula do well in pots, and along with cherry tomatoes provide healthy super-local produce — yet another reduction in their carbon footprint. One lesson Barbara’s learned about cherry tomatoes is not to crowd them. Plant just one to a large pot and prune assertively to be sure the energy goes into making tomatoes rather than excess foliage and that there’s sufficient air circulation.

cherry tomatoes ripening
Growing some food at home is fun and helps reduce the carbon footprint of food transport. Photo: Barbara Schuyler

While there’s some level of physical work involved, container gardening is within the reach of nearly everyone – no matter your available space, skill level, physical abilities, or budget. Start small. Share stories, plants, and pots with other gardeners, and enjoy the benefits for yourself, your community, and the planet!

Are you taking any steps in your garden to help mitigate and adapt to climate change? Have a story to share? Let us know! Leave a comment or contact us.

By Christine Hipple, University of Maryland Extension Master Gardener, Howard County, Maryland

Mix It Up! Perennial Vegetables

Most of us plan our gardens each year with abundant annual vegetables to harvest and enjoy. There are, however, several perennial vegetables you may want to consider adding to the mix, some familiar and others, perhaps, less so.

Perennial vegetables have some attractive benefits: they tend to be low maintenance, are generally easy to cultivate, high-yielding, and often more pest and disease resistant than their annual brethren. On the downside, they can be slow to establish and, if they do succumb to disease, will often need to be removed.

One critical consideration in planting perennial vegetables is location. These are perennials and once established some will not be easy to relocate or, as in the case of sunchokes, to eradicate, so site them thoughtfully. And be certain to clear away any perennial weeds before planting.

Following are just a few selections for Maryland, ones I have personal experience growing. The most comprehensive and enlightening reference by far is Eric Toensmeier’s Perennial Vegetables (2007, Chelsea Green Publishing), which offers a fascinating window into the many options available for our area.

Rhubarb (Rheum rhabarbarum)

Yes, rhubarb is a vegetable although we use it more like a fruit, sweetened in pies and sauces. (An annual rhubarb crisp endeared my neighbors to me!) It is the stalks we cut and use as the leaves and even though much of the flower heads are toxic to people and animals.

Root crowns should be sited in full sun with ample space (plant 3 feet apart) as the clumps can grow to be 3-5 feet wide. Rhubarb really prefers cold climates and our Zone 7 is about as far south as it will grow happily. A heavy feeder, it is good to provide extra nutrients with compost annually. Once mature, the attractive large-leafed clumps can be divided for propagation, which should be done every few years to re-energize the plant. Two or three plants will keep you in pies (but try it in savory stews and soups, too). Some growers recommend removing the showy flower stalks once they open. To harvest, twist or cut the stalk at the base and be certain to remove all of the leaves. Rhubarb will die to the ground in winter and in early spring you will see its lovely red buds swelling up from the earth. And you will know it is spring!

Ramps (Allium tricoccum)

Here it is, an easy-to-grow shade-loving vegetable that also happens to be delicious! Often referred to as wild leeks, ramps are native to eastern and central North America. These early spring bulbs have wide leaves compared to most onions, growing to about 10” long. They die back with the coming of summer.

Ramps are found in the wild in moist deciduous forests. They prefer rich, moist soil, much like woodland humus, and form small clumps that can slowly spread to form large colonies. Harvest the whole plant leaving some bulbs for next year, or simply harvest some leaves. The smallish bulbs are like onions or garlic, the leaves like scallions or leeks.

Ramps are being over-harvested in the wild. This is yet another good reason to start your own colony (and move some into that forested land nearby).

Sunchoke (Helianthus tuberosus)

Also known as Jerusalem artichoke (although neither an artichoke or from Jerusalem, go figure). These edible tubers are native to northeastern North America. Sunchokes grow 6-10 feet tall with cheery sunflower-like blooms in full sun or light shade. If sited in a wind prone area they will need support, or you can prune them back by a third to encourage bushier growth.

Sunchokes are very productive. Some varieties have knobby tubers while others are smoother (and easier to clean). They are sweet to the taste and rather nutty when roasted. Anything you can do with potatoes you can probably do with sunchokes. Harvest annually leaving some pieces of tubers with eyes 1-3 feet apart for next year’s crop. The flavor is best after a hard frost. A word about inulin: sunchoke tubers are high in inulin, a type of starch, which is not digestible by humans and can cause gas. Some people do not tolerate it well. Inulin does increase the ability to absorb calcium.

Here is where caution is required! Left to their own devices sunchokes will form large colonies – they are best treated like a mint using containing methods. I grew mine in a large raised bed and they gave me more tubers than I could use and a glorious mass of tall yellow flowers.

Cardoons (Cynara cardunculus)

Found in the wild all along the Mediterranean, cardoons are more popular as a food crop in Southern Europe and North Africa where they are native. They are related to globe artichokes but are grown for the edible stalks rather than the flower heads, which taste like artichokes and are used like celery. Their dramatic spiny silvery foliage and beautiful thistle-like flowers, however, have earned them a place in many gardens. Perhaps as architectural interest in a border? Bonus: Deer won’t touch them.

Cardoons do best in full sun and well-drained soil, although they tolerate some light shade. Start them from seed 6-8 weeks before the last frost and transplant them after the last frost date. The first year they can grow 3-5 feet tall and 3 feet wide, so plan some space. Plants have about a five-year productive life span. They can be divided in spring.

For eating, the stalks are usually blanched (protected from sunlight), to make them more tender and easier to cook, in the fall. This is done by tying the plant into a bundle and wrapping it with cardboard or newspaper to 18 inches then leaving it alone for a month. Hill up the soil around the stems. Cut the stalks off at ground level. Alternatively, you can harvest just some of the fleshy leaf stalks. Clean the leafy bits from the stalk (it will look like a celery stalk), peel away the outer skin, and parboil them before using them in recipes to mitigate any bitterness.

Asparagus (Asparagus officinalis)

Last on this list but probably the most widely known and loved perennial vegetable: asparagus. This edible shoot is a native of Eurasia but has naturalized throughout North America.

Asparagus can live for 15 years and longer, so situate it thoughtfully. (I well remember helping my dad pull out an ancient asparagus bed as a kid. Suffice to say it involved a tractor and chains.) It requires full sun and good drainage. Annual applications of compost or well-rotted manure keep it productive and plentiful water all season will keep it happy. It is easy to grow from seed but generally, year-old rooted crowns are planted in early spring to speed the time to harvest. Plant them 15-18 inches apart in wide beds or rows, with 4-5 feet between rows. All male varieties will not seed (females have berries) and tend to be more productive and disease-resistant. A broad selection of asparagus is available including lovely purple varieties (white spears are blanched).

Spears develop from the underground crowns in early spring. Do not harvest at all in year one and harvest lightly in years two and three. Spears should be snapped off or cut at 6-8 inches. After 8-10 weeks let the spears grow. They will form a lovely, tall, fern-like frond. After frost, the foliage will turn yellow, and at that point, it can be cut down to 2 inches. Asparagus can have a number of pests and diseases. Purchase resistant varieties, keep patches weeded and remove all foliage after frost for best prevention.

These are but a few of the interesting options available to you! 

More information about asparagus is on the Home & Garden Information Center website.

By Deana Karras, Baltimore County Master Gardener