Harvest Calculator

Dayboro Harvest Date Calculator

When will it actually be ready to pick? Based on my own station data, not Brisbane averages.

The most common question in my own garden, and I reckon yours too, is "is it ready yet?" I've been squeezing tomatoes and poking carrots out of the dirt for years to check, and I've learned that the number on the back of the seed packet is a starting point, not an answer. So I built this calculator. Pick your crop, pick your planting date, and it gives you the harvest window based on the actual temperature data coming out of my weather station 300 metres up the road. The Bureau of Meteorology still thinks Dayboro is warm. It is not.

Generic harvest calculators use textbook "days to maturity" figures based on ideal conditions. That is fine if you grow in a climate controlled greenhouse. In the Dayboro valley, where summer afternoons push past 35°C and winter nights drop to 4°C, growth rates shift dramatically with the seasons. A tomato I plant in October will mature faster than one I put in during March, because it spends more of its life inside the temperature sweet spot. This calculator accounts for that properly.

Harvest Date Calculator

Estimate harvest dates for 28 crops using live Dayboro temperature data from my own station.

Calculate Harvest Date

Earliest
Expected
Latest
Growth Progress 0%
Current Temperature Suitability
Germination:
Fine print: my harvest dates are approximations based on average days to maturity data adjusted for the current temperature on my station. Actual harvest timing depends on variety, your soil, watering, pest pressure, and microclimate details this calculator cannot fully account for. Use the dates as a guide, not a guarantee. Always check your plants for the maturity signs yourself (colour, firmness, size) before you pick.
Live temperature from my Dayboro Weather Station. Local growing conditions, not Brisbane averages.

Why I don't trust the seed packet number

Every seed packet has a "days to maturity" number on the back. Those numbers come from trials run in controlled conditions, usually in temperate North American or European climates with consistent day lengths and moderate temperatures. In the Dayboro valley at 130 metres elevation in the D'Aguilar foothills, conditions are different enough to make those numbers misleading. I've had tomatoes that were supposed to take 70 days come in at 55 (October planting, warm run), and I've had the same variety take 95 days (March planting, cool autumn behind it). Same seed, same bed, same grower. The only difference was the weather.

Summer temperatures here regularly push past 35°C, which stresses a lot of vegetables and actually slows them down. Winter nights drop to 4 to 8°C, which is fine for brassicas but brings warm season crops to a near standstill. The "days to harvest" for my Grosse Lisse might be 80 days on the packet, but in practice I've measured anywhere from 60 to 110 days depending on when I put them in. That is the range this calculator is trying to give you an honest answer inside of.

Growth speed depends on temperature, not calendar days: plants grow by accumulating heat, not by ticking days off. A warm week in January contributes more to maturity than a cold week in July. This calculator adjusts the textbook "days to maturity" based on how closely my station's current temperature matches each crop's ideal growing range. It is waiting on a live temperature reading every time you click the button.

How temperature affects growing speed

Every vegetable has an ideal temperature range for growth. Inside that range the plant grows at its maximum rate, and the seed packet estimate is roughly accurate. Outside that range, growth slows. Sometimes dramatically. I saw this myself last winter when my capsicum plants basically did nothing from mid June to early August, even though they were alive and green. The stem measurements barely changed. They were waiting on warmer air.

The way the calculator handles it is straightforward. If my station's current temperature sits inside the crop's ideal range, growth is modelled at a factor of 1.0 (normal speed). If it is too cold, the growth factor can drop as low as 0.3 (about a third of normal speed). If it is too hot (and yes, Dayboro summers genuinely can be too hot for some crops) the factor also drops, though less severely. This is why my lettuce bolts in February but thrives in May. Same plant, same soil, different temperature window.

Ideal ranges for common Dayboro crops

Crop Type Ideal Range Days to Harvest Germination
TomatoWarm18–30°C60–90~7 days
LettuceCool12–20°C45–60~5 days
CarrotCool15–25°C70–80~14 days
BroccoliCool15–25°C70–100~7 days
BeansWarm18–27°C50–70~7 days
PotatoCool15–22°C90–120~14 days
CucumberWarm18–30°C50–70~7 days
SpinachCool10–20°C40–50~7 days
CapsicumWarm20–30°C60–90~10 days
ZucchiniWarm18–30°C45–60~7 days
PumpkinWarm18–30°C85–120~7 days
CornWarm18–30°C60–90~7 days
RadishCool12–22°C25–35~4 days
GarlicCool10–22°C150–210~14 days
Sweet PotatoWarm20–30°C90–150~14 days
StrawberryPerennial15–25°C60–90~14 days
AsparagusPerennial15–25°C365–730~21 days

The table above is a selection of the 28 crops in the calculator. The range in days to harvest is enormous. I can pull radishes in under a month, while my asparagus bed took a full year before I dared to harvest a single spear. Garlic I plant in March is not ready until September or October. Once you plan your garden around these timelines you will have something to pick in every month of the year. That is what this tool is really for.

Frequently Asked Questions

How accurate are the harvest date estimates?
The estimates come from average days to maturity data adjusted for the current temperature on my station. In practice I've found they are a solid starting point rather than an exact prediction. Your soil, your watering, the pest pressure in your patch, and the specific variety you picked all shift the actual harvest date. The "expected" date assumes average conditions. The "earliest" and "latest" dates bracket the likely range. My own harvests usually fall somewhere inside that window, give or take a week.
Why does the calculator say my crop will take longer in winter?
Because plants grow by accumulated heat, not by calendar days. In Dayboro's cooler months (May through August), warm season crops like tomatoes, beans, and capsicum grow a lot slower. My station temperatures sit below the crop's ideal range. The calculator just reflects what I've measured in my own beds. Cool season crops like broccoli, lettuce, and peas actually grow faster in winter because they are finally in their preferred range.
What does the "growth factor" mean?
The growth factor is a multiplier from 0.3 to 1.2 that adjusts the textbook harvest timeline. 1.0 means the crop is growing at normal speed (the temperature sits inside the ideal range). Below 1.0 means growth is slower than expected. Above 1.0 means conditions are ideal and the crop may mature slightly faster than the seed packet promised. The factor is calculated from the current temperature on my station relative to each crop's own ideal range.
Can I use this for crops not in the list?
The calculator covers 28 common vegetables and herbs I've grown here myself. If your crop is not listed, find a similar one with comparable temperature preferences and days to maturity. Most chilli varieties behave like capsicum. Rocket is comparable to lettuce but a bit faster. The growth rate adjustment will still be useful even if the exact days to maturity figure is not perfect for your specific variety.

Methodology

The calculator uses a temperature based growth adjustment formula:

Growth factor calculation

For each crop, the current temperature from my Dayboro station is compared to the crop's ideal growing range:

  • If the temperature sits inside the ideal range: growth factor = 1.0
  • If below the ideal minimum: factor = 0.5 + 0.5 × (temp / optMin)
  • If above the ideal maximum: factor = 0.5 + 0.5 × (1 - (temp - optMax) / 15)
  • The factor is clamped to the range 0.3 to 1.2

Adjusted days to harvest

The textbook midpoint of the days to maturity range is divided by the growth factor to produce the adjusted estimate: adjustedDays = baseDays / growthFactor. A growth factor of 0.5 (cold conditions) effectively doubles the expected time. A factor of 1.2 (ideal conditions) shortens it by about 17%.

Data sources

The current temperature is fetched from /weatherdata/weather-current.json, which I update every 5 minutes from my Dayboro station (Ecowitt GW2000 + WS90, 130m elevation). Crop data (days to maturity, ideal temperature ranges, germination periods) is drawn from multiple horticultural references and calibrated against what I've actually measured here.

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