Choosing a vegetable garden app that knows your garden
Climate, soil, variety, stage and weather. An app must know these five things and use them. A five-minute test checks it.
An app that gives you the same sowing date in Lille and in Marseille knows nothing about your garden. To give the right date, it must know your climate, your soil, your variety, your plant's stage and the weather for the coming days. A five-minute test is enough to check that it uses them.
Vegetable garden apps, in three families
A 2022 study listed 606 apps related to plant diseases in three app stores. It kept 17 of them. Before installing one, look at the question it answers.
| Family | Your question | It relies on | Its limit |
|---|---|---|---|
| Calendar and plan | When to sow, where to plant | The climate of your area, sometimes adjusted for crops under cover | An average date if it ignores your variety and the weather |
| Identification | Which plant is this | A database of photos of plants already named | A blurry or badly framed photo fools it |
| Diagnosis | What is wrong | Photos of diseased leaves | It sees neither the underside, nor the whole plant, nor the rain of the past days |
These three families do not replace each other. An identification app tells you that your plant is a tomato. It does not tell you when to plant it. Photo diagnosis has its own guide, Identifying a sick plant with your phone. It shows the limits of a photo and the right way to photograph a diseased leaf.
Five pieces of information for the right date
1. The climate at your address
Climate weighs the most. Météo-France counts an average of 37.1 frost days a year at Lille-Lesquin and 20.3 at Marignane, near Marseille. In our data, the same tomato is planted on 15 May in northern France and from 25 March in the south of France. Seven weeks apart.
A good app asks where you garden. Often your town is enough. In Belgium, the Royal Meteorological Institute (RMI) publishes its climate statistics town by town. An app that asks you nothing serves you a national average.
2. The temperature of your soil
A seed does not read the calendar. It reacts to the warmth of the soil. In measurements from the University of California, a carrot takes 51 days to come up in soil at 5 °C. It needs 17 at 10 °C and 7 at 20 °C. A bean hardly germinates below 15 °C.
No app measures the temperature of your soil. At best, it estimates it from the weather. A thermometer pushed in at sowing depth still has the final say.
3. Your variety
Two tomatoes do not follow the same calendar. For northern France and Belgium, our data plant Marmande from 10 to 31 May. Cœur de bœuf is planted from 15 May to 15 June. An app that only knows "tomato" gives you an average date. For your variety, it is sometimes off.
Check that it lets you choose the variety on your seed packet, or at least the type (early, late).
4. Your plant's stage
A plant moves forward at the pace of the heat it receives, not of the days. A cold week slows it down. After a warm week, it is ahead. These are called growing degree days, explained in the growing degree days guide.
An app that counts the days since your sowing gives the same harvest date after a cold May or a warm May. If it follows the heat received, the date shifts.
5. The weather for the coming days
Climate normals give an average. The forecast talks about this week. In Lille, April still has 1.3 frost days on average. A planting date that is right on paper can fall the day before a frosty night.
The same goes for diseases. Tomato blight takes advantage of a few warm, humid days. The forecast announces them. The guide Tomato blight explains how to spot them.
The five-minute test
You can check everything before subscribing to anything.
An app cannot see your garden
Even well informed, it does not know the shade your wall casts from 3 pm. It does not know that your heavy soil warms up slowly or that one corner is sheltered from the wind. You know. A good app admits it and lets you correct it.
Identification apps have been measured. In a 2023 British study, five free apps received 857 photos of wild plants identified by specialists.
So even the most reliable one sometimes misses with its first answer. Read the next suggestions too and compare them with the plant in front of you.
What about Vegiwise?
We build Vegiwise in Liège. The app starts from your address to know your climate and your local weather. You tell it which varieties you have sown. Every day, it calculates the heat each plant has received to place its stage. Before a blight window, you get an alert. It cannot see the shade of your wall. You teach it that. To put it through the five-minute test, start here.
FAQ
Do you have to give your exact address?
No, not for the climate. Climate normals are published by weather station or by town. A precise address mainly serves the local forecast.
Can an identification app tell me when to sow?
No. It names a plant, sometimes a disease, from a photo. For sowing dates, you need a calendar matched to your climate, like our dates by region in France.
Is a free app enough?
To identify a plant, often yes. The five apps in the 2023 study were free. The right species was among their first five suggestions for 85 % of the photos. For dates matched to your garden, put the app through the five-point test, free or not.
And without an app?
A good calendar for your climate, a soil thermometer and the day's forecast already do most of the work. The sowing calendar for Belgium is made to be printed.
Photo: Markus Spiske, Unsplash
Sources
- Siddiqua A. et al., Evaluating Plant Disease Detection Mobile Applications: Quality and Limitations, Agronomy 12 (8), 1869, 2022
- Hart A. G. et al., Assessing the accuracy of free automated plant identification applications, People and Nature 5 (3), 2023 (857 photos, 5 applications)
- Oregon State University Extension, Soil temperature conditions for vegetable seed germination (données de J. F. Harrington, université de Californie à Davis)
- Météo-France, Fiche climatologique Lille-Lesquin, statistiques 1991-2020
- Météo-France, Fiche climatologique Marignane, statistiques 1991-2020
He gardens in Belgium and tries out in his own vegetable patch what the app recommends. His articles always start from a source you can check and a step you can take this weekend.
