What to Plant in Late Summer for a Fall Harvest

The beds look spent by mid-August. The lettuce has bolted, the peas are brown strings, and the tomatoes are so heavy they're pulling their cages sideways. It's easy to read that as the end of the season. It isn't. Late summer is one of the best sowing windows of the year, and the crops that suit it are quick, cool-natured and genuinely useful in the kitchen — crisp radishes in October, tender spinach for November soups, kale that sweetens after the first frost.

What changes is the arithmetic. You're no longer sowing into a season stretching out ahead of you; you're sowing into a countdown. Get that countdown roughly right and a fall harvest becomes the lowest-effort crop you'll grow all year: fewer weeds, fewer pests, far less watering once the nights cool.

Count Backwards From Your First Frost Date

Everything in fall planting starts with one number: your average first frost date. If you don't know it, your local extension service or a regional gardening guide will give you a range for your area. Write it down, then subtract.

Here's the rule worth using. Take the days to maturity on the packet, add two weeks for slower germination and shorter days, then add another week as insurance. That total is the closing date of your sowing window. A radish listed at 28 days really wants about 50 in the fall garden. A spinach listed at 45 wants closer to 70.

Those packet numbers assume long June days and warm soil. Neither applies in September. The buffer isn't pessimism; it's the difference between a real harvest and a bed of tiny leaves you're politely calling baby greens.

The Fast Lane: Radishes, Salad Greens and Herbs

Sow these first, while the soil is still warm enough for quick germination. Most go from seed to plate in under two months, and several can be cut young and repeatedly.

• Radishes. Twenty-five to thirty days for the small round types, and they tolerate cool weather better than almost anything. Sow thinly, every two weeks until mid-September.
• Arugula. Fast, peppery, best picked small. It bolts in heat, so a late sowing suits it. Sow thickly and cut leaves as needed.
• Lettuce. Choose loose-leaf and romaine types over tight head lettuces; they mature faster and shrug off cool nights. Start them in a partly shaded spot if afternoons are still brutal.
• Spinach. The prize of the fall garden. Sow in early September for October cutting; the leaves turn sweeter after a cold snap.
• Mustard greens and mizuna. Ready in three to four weeks for baby-leaf harvest. Flea beetles love them, so check the undersides of the leaves regularly.
• Cilantro and dill. Quick from seed and much happier in September than in July. Sow a short row every three weeks.
• Scallions. Slower than the rest — sixty days or so — but worth a row. They'll stand in the garden into cold weather.

Sow slightly deeper than you would in spring. Warm, dry soil dries out fast, and a seed sitting half a centimetre too shallow is a seed that never germinates. Then water daily until the seedlings are up.

Roots Worth a Late Start

Beets, turnips and carrots all appreciate shorter days, but they need more runway than salad greens. Beets and turnips are the safer bets: sown in late July through August, they size up in roughly two months, and their greens are edible too. Small beets are perfectly good beets, which takes some pressure off the calendar.

Carrots are trickier. Choose a short, stubby variety and sow by early August at the latest. Germination in hot soil is the main obstacle — cover the row with a board or a layer of burlap and check it daily, lifting it the moment you see green. If you're sowing into a bed that held garlic or early potatoes, you're in luck: that soil is usually loose and free of the big clods carrots hate.

For Brassicas, Buy Transplants

Kale, broccoli, cabbage and bok choy need too long from seed at this point for most gardeners. Buy transplants instead. A six-pack of kale set out in mid-August will be giving you leaves by October, while seed sown the same day is still a seedling when the frost arrives.

Set transplants slightly deeper than they sat in the pot, water them in well, and cover them immediately with insect netting or a light row cover. This is not optional in late summer. Cabbage white butterflies are at their peak, and the caterpillars that follow will strip a young kale plant to a skeleton within a week. Netting keeps them off without any spraying.

Bok choy and tatsoi are the exception worth sowing directly — they're fast, and a light frost improves them. Watch for slugs, which thrive in the damp, cooling soil.

Don't Forget Peas

A quick row sown in late July or early August will pod before the nights turn too cold, especially if you pick an early variety. Put the trellis up at sowing time rather than later; peas sulk when their tendrils are untangled and moved.

Getting Seed to Germinate in August Heat

The awkward part of fall planting is that you're sowing into summer conditions. Three things make the difference.

1. Water before you sow, then water again. Soak the bed the evening before. Seeds need consistent moisture through the first week, and a dry spell mid-germination is fatal.
2. Shade the seedbed. A sheet of shade cloth on hoops, or even an old window screen, keeps the surface cooler and stops it crusting over.
3. Keep sowing. Succession sowings every two to three weeks spread the risk. If flea beetles mow down your September arugula, the October sowing is already in the ground.

Once seedlings are established and the nights lengthen, fall beds need far less attention than summer ones: fewer weeds, less evaporation, less bolting.

This Week's Job List

Walk outside with a notebook and do three things. Find your first frost date and write it on the packet of everything you plan to sow. Clear one finished bed — bolted lettuce, spent peas, tired zucchini — and sow the fastest crop on your list into it. Then buy your brassica transplants and a length of insect netting, because both vanish from shelves quickly at this time of year.

After that, keep the hose handy for a fortnight and let the cooler weather do the rest. A fall garden rarely looks impressive in September. By November, when the tomatoes are a memory and the shops are selling pale, expensive greens, it looks like very good planning indeed.

Photo: flutie8211 / Pixabay