It can be too hot for lettuce in warmer areas of Australia during summer, although some of the loose-leaf varieties are more heat tolerant. Some light shade and a cool spot will allow lettuces to be grown in containers. Keeping lettuce seeds in an airtight container in the fridge can assist germination in warm weather.
If your area has a wet season in the next few months, it might be wiser to skip sowing sweet corn this month, as heavy rain will prevent good pollination. In cool climates, there is still time to plant fast-maturing varieties of pumpkin, rockmelon and watermelon. Seed for these can be ordered from Phoenix Seeds in Tasmania (PO Box 207 Snug, Tasmania 7054).
The following planting guide is an abbreviated list for vegetables, fruit trees and some culinary herbs that can be planted in August in Australia and New Zealand. A comprehensive monthly guide that includes planting times for the entire garden, as well as when to fertilise, prune, weed, take cuttings or divide plants, can be found in my book Easy Organic Gardening and Moon Planting.

Warm climate – South of Rockhampton
Before the Full Moon, silver beet, nasturtium and sunflower can be sown directly into beds, as well as a green manure crop of adzuki bean, cow pea, lablab, mung bean, pigeon pea, soybean, Japanese millet, millet, or sorghum.
During First Quarter phase, bush and climbing beans, eggplant and pumpkin can be sown directly into beds, and capsicum, rock melon, summer squash, tomato, watermelon and zucchini can be sown or planted out.
During Full Moon phase, beetroot, carrot, parsnip, radish, and watercress can be sown directly into beds. Banana passionfruit, lemongrass, passionfruit and dandelion can be sown or planted out, and banana, mango, pineapple and mint can be planted. Cuttings of mint, oregano, rosemary, sage, thyme, and watercress can be taken.

Warm climate – North of Rockhampton
Before the Full Moon, sow a green manure crop of adzuki bean, cowpea, lablab, mung bean, pigeon pea, soybean, Japanese millet, or sorghum.
During First Quarter phase, capsicum, tomato and watermelon can be sown or planted out.
During Full Moon phase, lemon grass can be sown or planted out, and mango planted.

Temperate climate
Before the Full Moon, cabbage, lettuce, silver beet, dill, nasturtium and sunflower can be sown directly into beds. Leek and spring onions can be sown as well as a green manure crop of adzuki bean, cowpea, mung bean, pigeon pea, soybean, millet, Japanese millet, or sorghum.
During First Quarter phase, bush and climbing beans and sweet corn can be sown directly into beds. Capsicum, cauliflower, cucumber, eggplant, rock melon, summer squash, tomato, watermelon and zucchini can be sown or planted out.
During Full Moon phase, beetroot, carrot, parsnip, and radish can be sown directly into beds. Banana passionfruit, passionfruit, dandelion, lemon grass and watercress can be sown or planted. Banana, mango, pineapple and mint can be planted. Cuttings of marjoram, mint, oregano, rosemary, sage, thyme, and watercress can be taken.

Cool climate
Before the Full Moon, cabbage, grain crops, lettuce, silver beet, tatsoi, dill, and sunflower can be sown directly into beds, as well as a green manure crop of adzuki bean, mung bean, soybean, cereal rye, millet, Japanese millet, or sorghum. Broccoli, Brussels sprouts, leek, lettuce, spring onions, sweet basil and parsley, can be sown or planted our. In warmer areas, NZ spinach and nasturtium can be sown directly into beds, and in colder areas bulb fennel, open-headed Chinese cabbage, and mizuna can be sown directly into beds.
During First Quarter phase, bush and climbing beans and sweet corn can be sown directly into beds, as well as suitable varieties of pumpkin, rockmelon and watermelon (see notes at beginning of post). Cauliflower, cucumber and zucchini can be sown or planted out, as well as summer squash in warmer areas only.
During Full Moon phase, beetroot, carrot, parsnip, and radish can be sown directly into beds. Dandelion, pyrethrum, sage, and watercress can be sown or planted out, and mint planted. Cuttings of rosemary, thyme, and watercress can be taken.