Mapping Your Balcony Microclimates
Before buying plants, watch how sun, heat and wind move across your balcony during the day. Most balconies have at least two kinds of spots: exposed areas along the rail and walls, and sheltered ones near corners or under an overhang.
Glass, concrete and brick can reflect and hold heat, which dries pots out faster. Wind tends to be stronger on higher floors, and it can pull moisture from leaves faster than roots in a small pot can replace it.
Look at your balcony in the morning, midday and late afternoon. Note where direct sun reaches pots, walls and floor, because those spots dry out fastest.
Selecting Herbs by Exposure
University of New Hampshire Extension says herbs generally need at least six hours of direct sun a day to do well. Match your plants to the conditions in each spot rather than buying only by what you like to cook with.
Sunny, Exposed Spots
Mediterranean herbs such as thyme, oregano and rosemary are generally adapted to bright sun and drier soil. Chives also cope well in a sunny spot as long as the pot does not dry out completely.
Sheltered Spots With Some Shade
Parsley, cilantro and mint tend to appreciate some relief from hot afternoon sun. Mint spreads by underground stems, so give it its own pot instead of sharing one.
Pot Size, Materials and Heat
UNH Extension says containers should be wide and deep enough for the herbs planted, and must have drainage holes. Pots that are too small dry out quickly, and pots that are too large hold excess moisture. On a hot, windy balcony, going up a size can make watering more manageable.
Unglazed terracotta is porous and lets the soil breathe, but it also dries out quickly in sun and wind, so check it often. Glazed ceramic, resin or fiberglass pots lose water more slowly. Dark thin plastic can heat up in direct sun, so shade the pot or choose a lighter color if the sun is strong. A potting mix made for containers drains better than garden soil.
Wind and Container Clustering
Wind is easy to overlook on a balcony. Grouping pots together against a wall or in a corner gives plants some protection and keeps light containers from tipping. Put heavier, low pots on the windward side and taller herbs behind them near the wall. Anchor tall or light pots so they cannot fall from a ledge.
Watering and Heat Waves
Water according to the soil, not the calendar. Push a finger into the soil: if it is dry a couple of inches down, water until it drains from the bottom. Wind dries the surface quickly, so the top layer alone can mislead you.
Most herbs prefer moist, well-drained soil. Rosemary prefers drier conditions, so UNH Extension recommends planting it on its own. During extreme heat or strong wind, move pots down to the floor against a wall for protection.
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