Garden Microclimates - What You Need to Know

If you spend much time in your garden, you know where the wind blows the hardest during a storm, where the sheltered areas are and where the soil tends to stay boggy or dry. Those choice or challenging spots are part of the ecosystem that is your landscape. The more you know about how your garden functions, the better equipped you'll be to grow the plants you REALLY want to cultivate.

Plant Hardiness Zones and Your Garden

Most gardeners rely on the Plant Hardiness Zones published by the U.S. Department of Agriculture (USDA) to help guide their plant choices. Zone recommendations are published on seed packets, added to those plastic seedling spikes included with new plants and referred to in articles like those posted here. I think hardiness zones are somewhat misunderstood, though. Here's why:

Many gardeners believe zone listings include more information than they actually do. Those numbers aren't the result of complex algorithms of multiple geographical and weather related characteristics. Zone designations refer to the average anticipated low temperature for a specific geographical location. That's it. Here's how the USDA puts it:

"Hardiness zones are based on the average annual extreme minimum temperature during a 30-year period in the past, not the lowest temperature that has ever occurred in the past or might occur in the future." (USDA Agricultural Research Service)

Zones don't take into account heat, humidity, or microclimate variables like proximity to water or buildings. These last two are particularly significant because they can have a big impact on temperature but are too localized to be evaluated by zone, even with the more specific "a" and "b" zone designations in use today. (More on that in a minute.)

Here's an example: You have a pond, creek or other water source near your home. Wind coming from that direction will be somewhat cooler that the surrounding air because soil, which is dense, holds heat better than water. As hotter air passes over a volume of water, its temperature drops. The reverse is also true: Developed areas with lots of concrete roadways and tall buildings will hold heat better than the surrounding undeveloped terrain.
Protected areas can be warmer in winter.

This is even the case on a smaller scale:

In summer, the shady side of your home will be cooler that the sunny side.

Elevated areas like decks and balconies will be cooler.

In winter, unprotected locations will be colder than sheltered areas.

If you live at the base of a hill or in a dale, your microclimate will likely be colder than the surrounding terrain because cold air is heavier than warmer air and will migrate to the lowest level it can reach.

If your home is on a south facing slope, your yard will be somewhat warmer that the folks on the other side of the hill with a northward facing garden.

These microclimates create conditions the savvy gardener can take advantage of -- or prepare for.

Test Your Garden -- It's the Only Way to Be Sure

So, if you think parts of your garden are warmer or colder than the norm, grab a thermometer and do some research. The difference between zones is actually 10 degree Fahrenheit for an average winter low. That number is further broken down by an "a" or "b" designation, an incremental difference of 5 degrees Fahrenheit.

In English, that means you can look at a zone map, discover you're in Zone 5b and be 5 degrees Fahrenheit away from a Zone 6 designation. Natural microclimates in portions of your yard or geographical area could easily adjust for the 5 degrees and open up a whole new world of plants for you. You may find you have a sheltered spot where rosemary will thrive, or a chilly corner with asparagus potential.

Proximity to water can affect climate.

Here are some tips on how to take advantage of microclimate variations:

Watch your garden this year. Take a look at where the sun shines in the morning and afternoon. Pay attention to how the wind blows. Review  topographical maps. Your findings should factor into your garden planning. 

You can Install the Google Earth to take a look at 3D maps for your area. The software/service is free. The installation page is here: Google Earth

You can also visit the U.S. Geological Survey site for access to maps for your area.  Start Here: USGS Map Locator & Downloader  

Invest in some outdoor weather temperature equipment and start making notes during hot summer days and cold winter nights. Focus on areas you think may be average, protected or particularly vulnerable.

This can be a more reasonable investment than you think. There are reasonably priced wireless weather stations that allow for up to three independent outdoor sensors. A system will include a convenient indoor console with a summary readout. (*Outdoor sensors are typically pretty durable. They run on batteries and have weatherproof cases.) Perform a web search on "wireless garden thermometers" for options. I know that La Crosse Technology (WS-9160U-IT Digital Thermometer) has one, but there are definitely others.

You can also use the old fashioned method, and position an outdoor thermometer where you want it and check the readout during peak hot and cold periods. (This may take some garden love when you're slogging through the snow in the middle of the night, though.)

Once you have a rough grid of your garden's microclimates, you can start investing in perennial plants with a real sense of what you can expect from them. You may be surprised at what you discover.

Happy gardening.

*Based on product reviews, these batteries can last up to a year.


Cornell University Gardening Resources, "Microclimates" (06/14/2013)


Watering Herbs in Pots

Although many herbs are hearty and pretty indestructible, they do need water -- and regular watering will help them perform better -- whether you're after leaves, seeds or flowers. If you're maintaining a patio or deck garden, I have a few tips that can help your dainty darlings survive the summer weather.

Get thee to the fridge -- This first one seems a bit unusual, but it works for me indoors and out. I read about it in an old newspaper article about keeping poinsettias. These classic Christmas flowers are thirsty devils, and to maintain them well takes regular watering. One wily gardener came up with the idea of "watering" his poinsettias with a couple of ice cubes a day combined with once weekly deep watering. As the cubes melted, they dispensed water in a gentle and reliable trickle the plants could absorb easily.

This is really an inspired idea. Here's why: When a plant's pot gets too dry, the soil becomes less able to retain moisture. Water -- when it does come -- just rushes through and exits from the bottom. Without enough dwell time, plant roots can't absorb nutrients effectively and go hungry. The plant begins to look needy, which can lead to a vicious cycle of overwatering. The result: the plant either dies of starvation from lack of water, or dies of starvation because its roots are sitting in too much water and rot.

The beauty of ice is that it's a cheap, natural and effective method of timed water delivery. I've been using it for years on many kinds of indoor and patio herbs as well as other plants and can say from experience this method works on tropical plants like orchids, African violets, spider plant, pothos and other classic houseplants. It also works on chives, parsley, oregano, ginger, lemon balm, mint, thyme, lemon eucalyptus, pineapple sage and other herbs.

I'll typically add four ice cubes to each six inch pot in the morning before things start to warm up, and repeat the process again in the evening. During hot summer months like July and August, I'll also water plants in the evening as needed -- usually a couple of times a week. For a large plant in, say, a 10 inch pot, I'll just shake six or eight ice cubes from a carafe.

Although I haven't had problems, I'm careful to keep ice cubes away from plant stems and leaves, positioning them on the soil or mulch. I haven't used this method with cactus plants, but it does work with immature aloe vera starts and jade plant.

If the prospect of micromanaging your greenery isn't appealing, using ice cubes is one of those "set it and forget it" activities you can perform before going to work in the morning, making it a regular routine. The amount of water in an ice cube may not seem significant, but more moisture will be absorbed by the plant than with conventional watering, so it provides decent coverage without the risk of over watering and killing plants -- or damaging your furniture if your plants are indoors.

Mulch more
- Adding mulch to a potted plant is like providing insulation to a home. It helps in temperature control and impedes evaporation. I like adding moss, but also use sand, stones and marbles. Outdoors I've even used shredded paper anchored with rocks. Works great. (It's also another way to get full value from that paper shredder. If you don't like the look of newsprint, try shredding paper bags.)

Pick a pot (no, not any pot!) - Self watering pots, thicker walled pots and non-terra cotta pots help conserve water. If you have a thirsty herb like catnip, basil, cilantro or dill, plant it properly in spring and you'll have fewer water related problems later. Oh, terra cotta pots that have been sealed on the inside work fine; unsealed pots absorb moisture, stealing it from the soil in dry weather.

Rube Goldberg devices - Upending a two-liter bottle (or burying one in the soil), as a water resource for a potted plant can work pretty well. I've done it myself, especially when I plan to be away from home for more than a day during hot weather. There are plenty of DIY tutorials around that can show you how to turn a plastic bottle into a garden reservoir. Watering Plants on Hot Summer Days

Shade is where you find it - Plants in dapples light typically require less frequent watering on hot days than plants in full sun. Planning some shade strategies now, like placing taller and more drought tolerant herbs on the sunny side of your patio to screen smaller, more delicate specimens, can make August easier on you and your plants. I've been known to move pots around to make the best use of sun and shade. I've even tented plants with shade fabric and bamboo screening. Just because you placed a tub of geraniums next to the Adirondack chair --where it does look neat -- doesn't mean your blooms have to stay in that spot forever. If you're dealing with a large pot, consider placing it on coasters to make moving day easier on your back.