Estimating a Balcony’s Microclimate: Four Illustrative Examples

Estimating a Balcony’s Microclimate: Four Illustrative Examples

This article contains a quick review of how to estimate your balcony’s microclimate and growing zone followed by four example scenarios to provide some clarity regarding how to navigate the ‘grey areas’ of assessing microclimate and growing zone. This is a companion article to How to Assess Your Balcony’s Growing Zone & Microclimate. I recommend going back to read it first before you continue reading this article.

Review: How to Estimate your Balcony’s Growing Zone & Assess Microclimate

The USDA Plant Hardiness Zone is based on the average annual minimum winter temperature over a 30-year period, not taking into consideration other factors like summer highs, length of growing season, humidity, or rainfall. While there’s no straightforward way to convert your balcony’s unique conditions into a precise USDA Zone, you can make an educated guess based on temperature observations and other conditions.

Here’s a step-by-step method to approximate the Plant Hardiness Zone for your balcony’s microclimate:

  1. Temperature Logging:
    • Invest in a min-max thermometer or small weather station for your balcony. This device records the highest and lowest temperatures within a given period. Here are my favorites.
    • Track temperatures over the colder months to determine the average lowest temperature. This is the primary criteria for USDA zones.
  2. Compare with Zone Maps:
    • Once you have the average lowest temperature, match it to the zone ranges. For instance:
      • Zone 5: -20 to -10°F
      • Zone 6: -10 to 0°F
      • … and so on.
  3. Adjust for Other Factors:
    • Even within a single zone, there can be great variability. Your balcony might have microclimate factors, like wind chill or radiant heat from walls, that can push it towards the colder or warmer end of that zone’s temperature range.
    • Additionally, consider factors like sunlight duration, humidity, and wind exposure. If, for example, your balcony gets prolonged direct sunlight, it might be conducive for plants from a half-zone or even a full zone higher.
  4. Observation and Experimentation:
    • Once you’ve made an educated guess, observe how plants fare over a season or two. Start with plants known to thrive in the approximated zone, then experiment a little. If a plant rated for a warmer zone thrives, you might lean towards your balcony having a warmer microclimate.
    • Take note of any plants that struggle, either due to cold or heat. Adjust your selections accordingly in the future.
  5. Cross-reference with Local Nurseries or Plant Apps:
    • Local nurseries can offer insights into what plants do well in balconies or microclimates similar to yours. They often have years of experience and feedback from customers.
    • Additionally, there are gardening apps that let you input specific conditions (light, humidity, temperature) and offer plant suggestions suitable for that environment.
  6. Ongoing Adjustments:
    • Climate conditions can change over the years, especially with factors like urban development. It’s a good idea to reassess your balcony’s microclimate every few years.

Remember, while the zone can give you a guideline, there’s no replacement for observation and learning from experience. By paying close attention to how plants respond to your balcony’s conditions and being willing to make adjustments, you can create a thriving garden space tailored to its unique microclimate.



Scenario 1: Mia’s Coastal Oasis in San Diego

Mia’s apartment is located near the coast in San Diego, California. She has a west-facing balcony that’s kissed by the ocean breeze. Here’s how she determined her balcony’s microclimate USDA zone:

  1. Temperature Logging:
    • Mia invested in a min-max thermometer and began logging temperatures in November. By February, she found that the lowest temperature her balcony reached was 42°F, and the highest winter temperature was 68°F.
  2. Compare with USDA Zones:
    • San Diego’s general USDA zone is 10a (30 to 35°F). Given that Mia’s balcony didn’t drop below 42°F, it seemed to align more with Zone 10b (35 to 40°F).
  3. Adjust for Other Factors:
    • The ocean breeze had a cooling effect during summer but also reduced frost chances in winter. The breeze also brought in slightly higher humidity levels.
    • Mia’s balcony, being west-facing, received intense afternoon sunlight, which could potentially allow plants from warmer zones to thrive.
  4. Observation and Experimentation:
    • Mia started with plants suited for Zone 10b and found they thrived. When she tried some plants from Zone 11a, like a specific variety of succulent, they also flourished, hinting that her balcony could handle some plants from warmer zones.
  5. Cross-reference with Local Nurseries:
    • When Mia visited a local nursery, the owner suggested some plants typical of Zone 10b that were popular among coastal residents. She also advised that Mia used pots with greater insulation to provide an extra layer of protection.
  6. Ongoing Adjustments:
    • Mia plans to keep an eye on the temperature trends each year, especially with the unpredictable nature of coastal weather.

Scenario 2: Leon’s Urban Space in Chicago

Leon lives in Chicago, Illinois, in a busy urban area. His balcony faces south but is partially shaded by a neighboring building. Here’s how Leon discerned his balcony’s microclimate:

  1. Temperature Logging:
    • With his min-max thermometer set up by early December, Leon observed that the lowest temperature during winter on his balcony was -5°F, while the highest was 35°F.
  2. Compare with USDA Zones:
    • Chicago typically falls under USDA Zone 6a (-10 to -5°F). Given that Leon’s balcony hovered at the warmer end of this zone, he considered it closer to 6b (0 to -5°F).
  3. Adjust for Other Factors:
    • The neighboring building provided some wind protection, reducing wind chills in winter. In summer, it cast shade during the hottest parts of the day, reducing extreme temperature spikes.
    • While the balcony received about 5 hours of direct sunlight, it was not as intense as it would be without the building’s shade.
  4. Observation and Experimentation:
    • Starting with plants typical of Zone 6b, Leon found great success. Encouraged, he even tried a few varieties that were labeled for Zone 7a and was pleased when they also thrived.
  5. Cross-reference with Local Nurseries:
    • A trip to a nearby urban plant nursery gave Leon insights into plants that urban dwellers with similar balconies had success with. They recommended a mobile app that helped him identify plants based on his specific conditions.
  6. Ongoing Adjustments:
    • Given the rapid urban development in his area, Leon plans to re-evaluate his balcony’s microclimate in a few years, anticipating potential changes in wind patterns or sunlight due to new structures.

Scenario 3: Ella’s Toroto Urban Jungle Balcony

Ella lives on the 15th floor of a high-rise in downtown Toronto. Her balcony faces north and is somewhat shielded by neighboring buildings. Eager to transform her space, she first consulted the Canadian Plant Hardiness Zone map and found Toronto is generally in Zone 6a.

To gain a more specific understanding:

  • Sun Exposure: Ella tracked the sunlight pattern for a week. While her balcony received indirect light throughout the day, it only got about 2 hours of direct sunlight in the late afternoon.
  • Surrounding Structures: The building adjacent to hers reflected additional light onto her balcony during the mornings, and its shadow kept her space cooler during peak noon.
  • Elevation & Floor Material: Being on a higher floor, her balcony was often subjected to winds. The concrete floor retained warmth well into the evenings.
  • Air Circulation & Moisture: The prevalent winds ensured that her balcony remained dry most of the time.

After her observation period, Ella deduced that even though Toronto was Zone 6a, her balcony’s conditions veered towards a cooler, windier version of that zone. She then opted for plants that enjoyed shade, were resilient to wind, and could handle the urban warmth radiated by the concrete.

Scenario 4: Raj’s Ground-Level Retreat

Raj resides in a ground-floor apartment in San Francisco. His spacious balcony faces east and enjoys a clear view with no immediate tall structures. He began his assessment by checking the USDA Plant Hardiness Zone Map, finding that San Francisco is within Zone 10b.

Delving into specifics:

  • Sun Exposure: Raj noted that his balcony enjoyed direct sunlight from sunrise until early afternoon, transitioning into shade by evening.
  • Surrounding Structures: Without any obstructive buildings, his plants received sunlight unencumbered. However, the fence around his balcony reflected additional morning light, causing one corner to be particularly bright.
  • Barrier & Protection: The wooden fence around his balcony provided a safeguard against any strong winds and also prevented any potential intrusions by wildlife.
  • Air Circulation & Moisture: The general atmosphere on his balcony was more humid, possibly due to the adjacent lawn, but a mild breeze kept the air fresh.

Taking his observations and the broader Zone 10b characteristics into account, Raj realized his balcony had a slightly more humid environment compared to the general area. With this information, he decided to go for plants that relished morning sunlight and prospered in a somewhat moist setting.