Rainy-season vegetables: raised beds, drainage, fungus, snails, what to plant
In the rains, vegetables die from waterlogging, not thirst. How high to raise beds, draining them, cutting fungal disease, snails without chemicals, what to plant.
- In the rains, roots fail because waterlogged soil runs out of air. Thailand's Department of Agricultural Extension recommends raising beds more than 30 cm above the ground.
- Slope the bed surface about 2%, and work at least one third coarse sand or organic matter into clay soil, so water doesn't sit.
- Cut fungal disease by watering at the base in the morning, weeding so air can move, and not crowding plants.
- Snails and slugs feed at night: hand-pick after dark, use board traps, and clear their hiding places around the bed.
Thailand’s rainy season runs from about mid-May to mid-October, with the heaviest rain in August and September. The problem in the vegetable bed flips from the hot season: plants don’t die of thirst, they die because standing water rots the roots, because damp-loving fungal diseases spread, and because snails come out at night to eat the leaves. The fix is to raise the beds, give water a way out, let air move through, and choose crops that suit the season.
This is lesson 14, following vegetables in the hot season. In southern Thailand the rain can continue to around mid-January, so the same approach applies for longer there.
Why soggy soil kills vegetables
Roots need both water and air. Soil that stays saturated pushes the air out of the pore spaces, and roots starved of oxygen begin to rot. Texas A&M’s raised-bed guide stresses that plant diseases develop much more easily in wet conditions, and that fungal diseases often appear where there is little air flow.
How high to raise the bed
The Department of Agricultural Extension (DOAE) notes that soil holds a lot of water in the rains, and recommends raising beds for shallow-rooted vegetables more than 30 cm above ground level. Texas A&M gives similar numbers: 20-30 cm is usually enough for a raised bed, and vegetable beds should be 30-45 cm deep.
| Bed type | Approximate height | Suits |
|---|---|---|
| Mounded bed, high centre, low edges | 20-30 cm | ground that doesn’t flood, just stays soggy after rain |
| Framed raised bed | 30-45 cm | clay soil, low spots, frequent standing water |
| Pots and troughs | lifted off the floor on bricks or stands | concrete yards, balconies |
Dry spells happen even in the rainy season. DOAE recommends watering regularly through them: fruiting crops that go short of water and then get heavy rain all at once can split their fruit.
Draining a 1 x 2 m bed, worked through
Say your soil is clay and you want a 1 x 2 m raised bed, 30 cm high. Step by step:
- Soil volume: 1 x 2 x 0.3 = 0.6 m³, or 600 litres.
- Texas A&M recommends amending clay with coarse sand, organic matter or coarse perlite at least one third by volume: 600 ÷ 3 = 200 litres. The other 400 litres can be your existing soil.
- Slope the surface about 2% towards where water will run off. On a 1 m wide bed sloping from the centre to each edge (50 cm), that’s about 1 cm of drop; sloping from one edge to the other, about 2 cm.
- Keep the paths around the bed lower than the bed, and make the paths carry water away to lower ground rather than back into the bed.
Don’t build a bed where a puddle forms after every rain; moving to higher ground is easier than fixing it later. For a basic soil mix, see starting a pesticide-free garden.
After a heavy rain, walk round the beds once. If water is still standing after half a day, that bed needs to be higher or needs a way for water to leave.
Cutting fungal disease
DOAE recommends steps you can take at home:
- Cover the bed with rice straw, dry grass or shade cloth to soften the impact of raindrops on bare soil.
- Weed so air can move, humidity drops, and pests have fewer places to live.
- Use seed from a reliable source.
- Space plants properly so leaves aren’t packed too tight for air to pass; Texas A&M notes fungal diseases tend to develop where there’s little air flow.
DOAE also suggests Trichoderma, a beneficial fungus mixed into compost or potting soil to help suppress disease-causing fungi. If you use it, follow your local agriculture office’s advice or the product label.
On watering: water the base, not the leaves, and water in the morning so foliage dries quickly. Sprinklers wet the leaves and make disease more likely. Mulch is still fine, as DOAE recommends, but keep a gap around the stems, and lift it now and then to check it hasn’t become a snail hideout.
Snails and slugs
Snails and slugs feed at night and hide by day under anything cool and damp, so often all you see are holes in the leaves and shiny slime trails in the morning. UC IPM (University of California) recommends:
- Hand-pick after dark. Use a torch under leaves, around pot rims and along bed edges.
- Board traps. Lay a board on runners about 2.5 cm high; snails gather underneath. Lift it and collect them every morning.
- Remove hiding places such as piles of bricks, loose boards, upturned pots and weeds near the bed.
- Water in the morning, not the evening, so the surface dries before night.
- Copper bands about 10-15 cm wide around the edge of a raised bed help stop snails climbing in.
If you need a bait, iron phosphate baits are safer around children, dogs and wildlife; metaldehyde can poison dogs and birds. Always read the label, and know that bait alone isn’t enough: you also have to remove shelter and moisture. More non-chemical methods are in natural pest control.
What to plant in the rains
DOAE lists vegetables that do and don’t suit the rainy season:
| Suits the rainy season | Doesn’t suit the rainy season |
|---|---|
| Short-cycle leafy greens: pak choi (kwangtung), Chinese water spinach, lettuce | Onion |
| Climbers: ivy gourd (tamlueng) | Shallot |
| Legumes: garden pea, yard-long bean | Garlic |
| Cucurbits: cucumber, pumpkin, wax gourd, bitter gourd, luffa | Carrot |
Save bulbs and roots like onions and carrots for after the rains. Train climbers like ivy gourd, bitter gourd and luffa up a trellis so the bed stays open and the fruit is easy to pick.
Common mistakes
- Planting flat in a spot where water pools. Roots rot before the plants get going.
- Crowding plants. Leaves touch, air can’t move, foliage stays wet and disease spreads quickly.
- Watering in the evening right after rain. The soil stays soggy all night, and snails love it.
- Mulching and never checking underneath. Cool, damp mulch can become a snail shelter.
- Forgetting to water in a dry spell, assuming the rainy season means no watering at all.
Sources
- Advice for caring for vegetables in the rainy season, from the Department of Agricultural Extension (Thai) — Daily News
- Country Report Thailand: seasons — Thai Meteorological Department / WMO
- Building a Raised Bed Garden (E-560) — Texas A&M AgriLife Extension
- Quick Tips: Snails and Slugs — UC IPM, University of California
- Watering Wisely: How Much Your Summer Vegetable Garden Really Needs — NC State Extension
FAQ
Do I still need to water in the rainy season?
Not on days it rains, but dry spells happen. When the rain stops for several days, water as usual. The Department of Agricultural Extension warns that fruiting crops that go short of water and then get heavy rain can split their fruit.
Do beer traps work for snails?
Yes. UC IPM suggests burying a container of beer with its rim at soil level; snails crawl in and can't get out. Check and empty it every day. It works better alongside hand-picking and removing hiding places than on its own.
Can I grow lettuce in the rainy season?
Yes. The Department of Agricultural Extension lists lettuce among the short-cycle leafy vegetables suited to the rains, but raise the bed so water can't pool, and don't crowd the plants: leaves that touch and stay wet rot easily.
General information, not medical advice. If you are pregnant, take regular medication, or have a liver or kidney condition, ask a doctor or pharmacist before taking herbs beyond normal food amounts.