Count the sun hours on your balcony or yard, then pick crops that fit

Before you buy seeds or pots, count how many hours of direct sun your spot gets in a day. That number decides almost everything. With 6 hours or more you can grow fruiting crops such as chillies and eggplant; with about 3-6 hours, stick to leafy greens and shade-tolerant herbs.

This is the first lesson of the path “Grow your own vegetables, from sunlight to plate”. If you have never grown anything, the overview in Start a pesticide-free garden in a small space is a good warm-up. This lesson is only about sun.

Direct sun, dappled light and shade

Direct sun is when sunlight lands on the leaves with nothing in the way; stand there and you see a sharp shadow. Dappled light comes through leaves, netting or a window screen, and the shadows are soft and spotty. Shade is bright but with no sun falling on it at all, such as under a deep roof overhang.

The terms on seed packets and in growing guides mean roughly this:

Term	Direct sun per day	Suits
Full sun	6 hours or more	Fruiting crops; every vegetable grows best here
Part sun	About 3-6 hours	Leafy greens, spring onions, coriander, some root crops
Dappled / light shade	Under 3 hours, or filtered	Culantro and truly shade-tolerant plants only

Sources do not agree exactly on the middle band: some say 2-4 hours, others 3-6. Use it as a guide, not a hard rule. The important part is that the hours do not need to be continuous. Three hours of morning sun plus three of afternoon sun counts as six.

How to count sun hours in one day

You need a clock and paper, or a phone camera.

1. Pick a clear day. Put an empty pot or a chair where you plan to grow, at leaf height.
2. Every hour from 7 a.m. to 5 p.m., check whether that spot is in direct sun. A photo works too.
3. Write it down in a row: one mark for direct sun, another for filtered light or shade.
4. Count the direct-sun marks. That is roughly your number of hours.

If you can, repeat it when the season changes. The sun’s angle in Thailand shifts enough to change the same spot by several hours.

Worked example: an east-facing condo balcony

Say you log this in October:

• 7:00 to 11:00, direct sun every hour = 4 hours
• 11:30, the overhang starts to block it; add half an hour = 4.5 hours
• The whole afternoon is shaded, with a building blocking the western sun

About 4.5 hours in total puts it in part sun. The spot suits lettuce, choy sum, spring onions and coriander, which will grow a little slower than in full sun but still give you plenty to pick. Tomatoes and chillies would flower and set fruit poorly there, and are not worth the space.

If you really want chillies, look for more sun: the outer edge of the balcony, where the overhang blocks the sun later. Moving a pot just 50 cm can sometimes gain an hour.

How much sun each group needs

Every vegetable does best in full sun. The difference is that some groups “tolerate shade” and others do not.

Group	Direct sun needed	Examples from a Thai kitchen
Fruiting crops	6-8 hours	Chillies, eggplant, tomatoes, yard-long beans, cucumbers, luffa, pumpkin
Leafy greens and cabbage family	Tolerate part sun	Lettuce, choy sum, Chinese kale, mustard greens
Small roots, spring onions	Tolerate part sun	Small radishes, spring onions
Coriander	Tolerates part sun; likes some shade in the hot season	Coriander
Prefers shade	Dappled light	Culantro (sawtooth coriander)

The reason is simple. Fruit and seed take a lot of energy, so the plant has to photosynthesise long enough to have energy left for flowering and fruiting. Leafy greens are picked young, so less sun only slows them down.

Some crops even like a bit of shade. Lettuce grown in long hot sun tends to turn bitter. Coriander in heat and strong sun rushes to flower and stops giving leaves. Culantro grown in shade flowers later and gives more leaves.

Count the sun first, then choose the crop. Do not choose the crop and hope the sun will be enough.

Balcony direction in Thailand changes with the season

Thailand is close to the equator, so the sun is not in the south all year as it is in cooler countries. The National Astronomical Research Institute of Thailand (NARIT) explains that the sun passes directly overhead Bangkok twice a year, around late April and mid-August. Between those dates the noon sun sits slightly to the north; for the rest of the year it is to the south, furthest south in the cool season.

What that means for a balcony (a tendency only; surrounding buildings can change it a lot):

Balcony faces	Cool season (Nov-Feb)	Mid-year (May-Jul)
South	Most sun of the year	Less sun; the overhang blocks more
North	Almost no direct sun	Some direct sun
East	Morning sun	Morning sun
West	Afternoon sun, very hot	Afternoon sun, very hot

Morning sun is usually kinder to vegetables than afternoon sun: the air is still cool and dew dries off the leaves quickly. A west-facing balcony collects many sun hours, but Thai hot-season afternoons are fierce, and leafy greens may need some afternoon shading.

In the far north or south of Thailand the overhead dates differ from Bangkok’s, but the rule is the same: count again when the season changes.

Common mistakes

• Counting brightness instead of sun. A room that is bright all day but never gets direct sun will give you leggy fruiting plants with no fruit.
• Counting one day and using it all year. A balcony that is sunny in December may get much less in mid-year.
• Pushing pots against the inner wall. Overhangs and railings block more than you think; measure at the outer edge too.
• Putting fruiting crops in a 4-hour spot. The plant may survive but fruit poorly. Leafy greens in that space would feed you more.
• Forgetting that the neighbour’s tree grows. A big tree that leafs out in the rainy season adds shade every year.

Once you know your sun hours, the next lesson is mixing potting soil and choosing a pot big enough for each crop.

Sources

• Sunlight Hours — Chicago Botanic Garden
• No yard? Grow vegetables in containers — Oregon State University Extension
• Vegetable Gardening in Containers (E-545) — Texas A&M AgriLife Extension
• Best crops for shady garden spots — RHS
• Culantro — UF/IFAS Gardening Solutions
• See the sun at its Bangkok overhead zenith — The Nation (NARIT)