And, if you want winter veges like broccoli and cauliflower, to be ready to eat in winter, plant them towards the end of march while the weather and soil is still warm enough to give them a kick start. If you wait till May you'll end up with broccoli in spring when you might be more interested in eating veges like lettuce.
Spinach is perfect to plant amongst your leek seedlings because you'll harvest it before the leeks need the space. Spinach is a fantastic plant. Slugs don't like it, you can eat it when it's young or old, it grows in dry and wet and just about all year round, and it's perfect for quiches and salads. You just need to make sure you eat it before it goes to seed.
Keep harvesting and don’t forget to keep watering. Remember March can still be quite a warm time of year.
Lastly, before the temperature drops too much, move any chilli or capsicum plants to somewhere warmer like a glasshouse or indoors. These plants can survive for a couple of years if they’re warm enough and will often produce better crops in their second year.