Lesson 5
Containers, compost and water management
Containers must not tip, shatter or leak. Plastic is the only sensible choice. Choose squat, wide pots with a low centre of gravity — tall thin pots topple on corners. Self-watering containers (with a reservoir at the base) are worth every penny: they extend watering intervals from one day to three or four.
Compost matters more in a van than in a garden. Standard multipurpose dries out fast and compacts hard. Add 20–30% perlite or vermiculite to improve drainage and aeration. Water-retaining crystals (hydrogel) can extend watering intervals, but use sparingly — too much and the compost turns to gel. Coir-based composts hold moisture better than peat-free blends, and they weigh less.
Watering is the single biggest challenge. A 15cm pot in full sun can need 150ml daily in summer. If you park for three days, that is 450ml per pot — half a litre. The maths gets brutal fast. Group pots together to reduce evaporation. Use drip trays to catch runoff and let roots reabsorb it. Water in the evening, never in midday heat.
Automatic solutions: a gravity-fed drip irrigation system (fed from a 5-litre bottle) can water six pots for a week. Self-watering wicking systems use a felt strip to draw water from a reservoir. For short trips, group plants in a large tray, water heavily, then cover loosely with a plastic bag to create a humid microclimate.
Quick reference: container sizes
- Herbs (basil, parsley, thyme): 12–15cm diameter, 1–2 litres
- Salad leaves: shallow trays, 5–8cm deep, any length
- Microgreens: seedling trays, 3–5cm deep
- Dwarf tomatoes: 5–10 litres (bigger = better yield)
- Chillies: 12–15cm pots, 2–3 litres
- Radishes, spring onions: 10cm depth minimum
Setting up a simple self-watering pot
- 1.Choose a plastic pot with drainage holes and a matching drip tray.
- 2.Place a 2–3cm layer of gravel or perlite in the drip tray.
- 3.Stand the pot on the gravel; fill the pot with compost mixed with 20% perlite.
- 4.Water the compost from above until water runs into the tray.
- 5.Top up the tray reservoir every 2–3 days; the compost wicks moisture upwards.
- 6.Check compost moisture with your finger — if the top 2cm is dry, add water to the tray.
- 7.Every two weeks, water from above to flush out salts and refresh the root zone.
Weigh your pots when freshly watered, then when dry — you will learn what 'needs water' feels like in your hand.