The bottom line: Since this month tends to be unpredictable weather-wise, have row covers at the ready for any late-season frosts or freezes that might damage perennials.
Outside: Most vegetables prefer a slightly acidic soil (6.0 to 6.8 pH); pick up a pH test kit at a garden center to make sure yours is in the right range. No such luck? Make adjustments as recommended on the package, using organic matter to increase or decrease the soil’s acidity. Even if your test is good, you should amend the soil—i.e., add conditioners, such as compost, peat moss, or coir (coconut fiber), that improve its texture—yearly, and give perennial vegetables a boost by “side dressing” it with organic compost or aged manure. (Scatter the fertilizer along the sides of a row of plants; turn it into the existing soil with a spading fork and rake it smooth.) If you’re stuck with soil that’s beyond saving, consider building raised beds instead and filling them with good soil.
Inside: Start seeds of warm season crops such as tomatoes, peppers, eggplant, pumpkin, snap beans, squash, and sweet corn.
Use a garden thermometer to determine if the soil temperature is at or above 40ºF. When it gets there, start planting (or “setting out,” in garden lingo) the seeds you’ve started for cool-season crops: kale, lettuce, spinach, and onions.
At the end of the month, plant peas. If the ground is wet and muddy, hold off so you don’t destroy the soil by working in it too soon.