Wait until nights are reliably above 50 °F, says the summary at the top of this search, and the horticultural society under it agrees. In Celsius that is 10 degrees, which is the same number our cold alert uses. We did not copy it: our threshold started at 4 °C and a horticulture review moved it up, on the grounds that tropical foliage starts suffering around 10 to 12 rather than at freezing.
So the temperature half is settled, and it is worth saying plainly that this is a forecast question rather than a date question. There is no month at which it becomes safe, and no last-frost date that applies to a flat in a different hemisphere. What matters is the run of nights ahead of you.
Not the best fit right now
The plant's fine, this spot just isn't a match.
Too bright here
Comfortable temperature
Humidity suits it
Airflow doesn't suit it
Light is a deal-breaker here. The other three cannot make up for it.
What the light does when you open the door
Here is the part the temperature answer leaves out. A plant that has spent the winter on your brightest sill has been reading a fraction of what falls on your balcony, and a smaller fraction again of open sky. Hold everything else and move only the doorway:
| Where it is standing | Estimated light | Verdict |
|---|---|---|
| Indoors, at the window | 3,640 lux | Great fit, 100/100 |
| On a balcony | 7,000 lux | Worth a try, 67/100 |
| Outdoors, in the open | 12,000 lux | Not the best fit right now, 45/100 |
That is one plant, one aspect, one clear day, and the verdict flips from workable to too much without anyone changing a species or a season. Glass, and the angle it sits at, is doing more work than most people give it credit for. Our page on how bright a room can actually get works the indoor ceiling out in detail.
Five plants, one open spot
Which is why "put your plants outside for the summer" is not one piece of advice. It is a different instruction per plant, and the split does not follow the tough-plant reputations either:
| The plant you carry out | What the light is doing | Verdict |
|---|---|---|
| Peace lily | Too bright here | Not the best fit right now, 42/100 |
| Monstera | Too bright here | Not the best fit right now, 43/100 |
| Snake plant | Too bright here | Not the best fit right now, 43/100 |
| Jade plant | Just the right amount of light | Good fit, 82/100 |
| Aloe vera | Just the right amount of light | Good fit, 82/100 |
Every row read the identical light in the identical spot, and the split is clean rather than gradual: the two succulents are comfortable, and the three that get recommended for low corners are all past their limit. Toughness indoors usually means tolerance of dimness, which is the opposite of what an open sky asks for. Shade outdoors is the fix, and it is not the same thing as shade indoors.
The watering changes at the threshold too
There is a third change, and it happens the moment the pot is on the other side of the door. Indoors, our watering model does not use the weather as it arrives:
| Where the plant is | What the watering model reads for it | In short |
|---|---|---|
| Indoors | The forecast day converted to a room equivalent first: the temperature pulled toward a room baseline, the daily swing flattened, the air taken as still and the light as overcast | Room equivalent |
| On a balcony | The forecast day itself, discounted for shelter at ×0.8 on the reasoning that a balcony usually has a roof, a wall, or both | Sheltered |
| Out in the open | The forecast day itself, with nothing taken off it: the real wind, the real swing between day and night, and the real sunshine | As forecast |
Rain, wind and snow alerts work the same way: they exist only for a plant that lives outdoors, because a wall stops all three. Heat and cold are the two that follow a plant indoors, and the five events and their thresholds are set out on the page for the journey in the other direction.
What to do with yours
Watch the nights rather than the calendar, and give it a week of shade outdoors before anything sunnier. Take a reading in the spot you are actually planning to use, with the free spot checker if you would rather not install anything, and take it at the time of day the plant will be sitting there. Then expect to water more often than you did indoors, for the reason in the table above rather than because the plant is thirstier, and read what else moves that interval before you change anything else. A summer outside also settles the feeding question, since the light half of that test is cleared by open sky on any day of the year.
The verdicts here come from the same spot check the app runs, with temperature, humidity and airflow held at one set of values so the only thing moving is the one named in each table. Light figures are estimates for a clear day rather than meter readings, and the balcony discount is a calibrated model constant rather than a measurement of your balcony.