Garden Microclimates: Shrug Off Your Growing Zone

Ignore those Zone limitations and find areas in your garden where traditional growing advice doesn’t apply.

| October/November 2019

Microclimate
Photo from GrowVeg.com

When I worked as a commercial gardener, one of the most interesting things I learned about was the influence of microclimates. Even though all the gardens I maintained were within 30 miles of each other, I soon discovered that what grew well in one garden was no sure indicator of what could be persuaded to thrive in another — even when the other garden was right next door! Conventional wisdom states that what a gardener can grow is limited by the USDA Hardiness Zone they’re gardening in, but I’ve found that isn’t the whole truth. Another important factor should also be taken into consideration: every garden’s unique microclimates.

Season extenders, such as row covers, are invaluable for warming up soil and protecting crops from the elements, but smart gardeners can deploy many more powerful techniques. By becoming aware of and manipulating the microclimates that make up your plot, you can improve yields and successfully grow crops that are on the borderline of what’s feasible in your region.

Microclimate
A fan-trained fruit tree grows against a wall, a heat sink that provides additional warmth. Photo from GrowVeg.com



Identify Your Microclimates

To exploit the microclimates in any garden, you’ll first need to learn exactly what they are. This often-overlooked task shouldn’t be rushed; it’s best done at several points during the year to gain a complete picture of how your garden changes through the seasons.

First, ask yourself four questions:

  1. Where is heat stored in my garden? Heat doesn’t just disappear when the sun goes down. Stone, brick, concrete, and even water absorb heat during the day and release it at night, a phenomenon known as “thermal mass.”
  2. Which areas are exposed? Strong winds can chill tender seedlings, flatten plants, snap plant supports, and dry out soil. Wind tunnels — areas where wind is forced between solid objects, effectively increasing wind speed — can be particularly destructive.
  3. Which areas of my garden receive the most sunlight, and how does this vary throughout the seasons? Shadows cast by trees, buildings, and other structures are short in summer and long in winter. What may seem like an unpromising spot in winter can be sun-soaked in summer, and vice versa.
  4. Where does water pool when it rains? Low spots and areas with heavy soil or poor drainage hold water longer, which can be useful in dry regions, or a plant killer in wetter climates.

Once you’ve observed and identified these areas on your property, the next step is to take advantage of them to grow plants that conventional wisdom tells you aren’t possible for your Zone.

Microclimate
Frosted plant leaves and other gardening problems can be avoided by creating habitable microclimates. Photo from Ann Marie Hendry

Keeping Warm

Remember the gardens I mentioned earlier that were near each other? Both experienced the same chilly winters and cool summers; had clay soil and poor drainage; were surrounded, at a respectful distance, by trees and hedges that filtered the worst of the wind; and had some areas in full sun for most of the day. They also received the same annual pruning and regime for soil enrichment.

But one garden grew prodigious quantities of apples, pears, and currants, while the other struggled to produce even a light picking of fruit. The difference? Thermal mass.

Stone walls completely enclosed the productive garden. Soft fruits grew against the walls — even the north-facing one — and they thrived. Heat absorbed by the walls during the day was released at night, keeping frost at bay and crucially preventing damage to delicate blossoms in spring, which resulted in generous bumper harvests.

Microclimate
Add sawdust mulch to acid-loving plants. Photo from Ann Marie Hendry

Walls, paving, rocks, and water barrels can act as “heat sinks,” or sources of thermal mass, to raise temperatures by a few precious degrees. With lessons learned, I transplanted several soft-fruit bushes against the house in the problematic garden. The move had the happy result of improving yields to almost match those in the more sheltered garden next door.

Another way to minimize frost damage is to remove, or at least avoid planting in, frost pockets. Cold air will sink into dips and hollows in your garden, so if you need to grow in those, fill them in to bring them up to the surrounding ground level. Or, go one step further and grow plants on mounds or in raised beds.



Frost pours away downhill, so make sure cold air can escape by removing any solid barriers that might impede its progress and cause it to pool in your growing areas.

Microclimate
Brassicas love grass mulch for its nitrogen. Photo from Ann Marie Hendry

Cold tolerance is a sought-after trait in plants, so plant breeders make great efforts to select for this when developing new varieties for cooler areas. Choose varieties specifically bred to be hardy in your Zone, which will make a considerable difference to your chances of success.

Creating Windbreaks

Strong winds can rip plants and greenhouses to shreds, as I’ve learned at my own cost! My garden sits at the head of a valley that channels the prevailing wind. When the wind forces its way between the house and garage, it speeds up and becomes even more powerful — right before it hits my greenhouse. If only I’d built a hoop house, whose curved profile and plastic cover would have saved me several trips to the glazier!

Windbreaks are the obvious solution to windy situations, but the fix isn’t as straightforward as building a wall or putting up a panel fence. The problem with solid barriers like these is that they force the wind to divert up and over — and then come crashing down, potentially smashing your greenhouse or flattening plants.

Microclimate
A willow hurdle air-permeable fence protects plants from wind. Photo from GrowVeg.com

Instead, opt for permeable barriers. These types of barriers slow down wind, while still enabling it to continue on its path. Hedges make superb windbreaks for this reason, but even netting securely attached to stout posts can help reduce the force of wind. You may need to combine the two and use windbreak netting to protect a young hedge while it becomes established in a windy spot. Consider growing an edible hedge of fruits or nuts to make your windbreaks an even more essential part of your productive garden.

You can reduce the impact of wind in other ways too. Gardening in sunken beds is an effective method sometimes used to provide shelter in flat regions. Six inches deep is enough to protect delicate seedlings.

If you need to go much deeper to protect mature plants, consider creating berms as well. These mounds will deflect wind, channeling it away from your precious plants. Bear in mind that sunken beds will be more prone to waterlogging, so they’re not usually suitable for heavy soils.

Microclimate
This sheltered corner of the garden is protected from blustery weather with a hedge windbreak. Photo from GrowVeg.com

Careful plant choices can make even the windiest spots more promising. Choose bush beans instead of pole beans that can be torn to ribbons, or let squashes, cucumbers, and tomatoes trail over the ground instead of supporting them on fragile trellises. Narrow-leaved onions and garlic are usually more resilient than broader-leaved or top-heavy vegetables, such as kale, that tend to blow over.

Sun and Shade

Where shade falls in your garden will vary according to the time of day and the season. Even if your garden is shady for most of the afternoon, you can still grow a wide range of vegetables if it receives morning sun. Leafy greens, bush beans, carrots, beets, and celery are all happy with just a few hours of direct morning sunlight.

You should plan to grow plants at wider spacings in a shady spot. They need to be able to absorb as much light energy as possible, so causing further shade by planting too close will reduce your harvest. To enhance the available light, wrap a board in aluminum foil and prop it up nearby, or paint a light color on vertical surfaces to reflect light back onto plants.

Microclimate
Ask yourself whether your plants need a shaded or sunny (below) spot to thrive in your garden. Photo from GrowVeg.com

Shade is often considered a bad thing in a garden, but you can use it to your advantage if you grow crops that might struggle in full sun — a real benefit in hotter climates. Crops such as lettuce, arugula, and beets are prone to bolting in hot weather, but you can delay the inevitable by planning your garden so these crops grow in afternoon shade.

It’s possible to create temporary shade in even the hottest, sunniest garden. With a little bit of clever planning, you can grow shorter, heat-averse plants, such as lettuce, on the north side of taller, heat-loving crops, such as tomatoes, to benefit from the shade they cast.

Microclimate
Photo from GrowVeg.com

For a more temporary solution, suspend shade cloth above cool-season vegetables, or use vertical barriers on the south side of susceptible plants. Straw bales are easy to move into position, and can be used as mulch, or added to your compost pile when you’re done with them.

Water Management

Areas where water is slow to drain are ideal for growing thirsty crops in hot summers, reducing the frequency of watering required. These same areas will warm up more slowly in spring, however, so avoid using them for your earliest plantings.

Microclimate
From left: If your plants need more water, add a water bottle reservoir. Photo from GrowVeg.com

Mulching with organic matter can also help sandy soils retain moisture, which is welcome in warmer conditions. Anyone gardening in a hot climate, or just enduring a hot summer, knows how quickly watering becomes a time-consuming chore, even in smaller gardens.

Microclimate
To avoid soggy soil, position your plants on mounds. Photo from Ann Marie Hendry

A nifty trick for gardening on dry soils or slopes is to plant into a shallow depression made in the soil, so the plant sits slightly lower than the surrounding soil level. When it rains, or when you turn on the hose, water will collect around the plant. Pooling gives water time to soften the crust and percolate down; this is particularly good for soils that dry to a hard crust, making it difficult for water to penetrate.

If high rates of evaporation mean that water doesn’t get a chance to penetrate deeply into your soil, you can deliver a shot of water straight to the roots using an olla. A traditional olla is an unglazed earthenware container that you sink into the ground and then fill with water. Because terra cotta is porous, the water gradually escapes into the soil at the root zone. You can achieve a similar effect by cutting the bottom off a plastic bottle and punching holes into the cap and neck. Partially bury the bottle top-down in the soil, and then pour water into the open end.

Microclimate
Managed microclimates can bring about an abundant harvest! Photo from Ann Marie Hendry

A garden is a long-term project. Take the time to observe your property and note its quirks. Discovering your garden’s limitations and possibilities is key to successfully growing food in any climate. Get to know your plants; take note of how other gardeners near you have overcome challenging growing conditions; and use your knowledge, experience, and skills to grow more than you ever thought possible.

Microclimate
Swiss chard plants grow in raised beds to avoid wet soil. Photo from GrowVeg.com

And remember, if your neighbor seems to have a greener thumb than you, the answer may lie in their garden’s microclimates and not just their gardening skills!


Ann Marie Hendry is a writer for GrowVeg.com, and is one of the expert gardeners supporting customers of the MOTHER EARTH NEWS Garden Planner.

 






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