Month-by-Month Lethbridge Garden Calendar

The year at a glance

Two dates anchor everything: at the Lethbridge research station, there’s about a one-in-three chance of frost after May 25 and about a one-in-three chance before September 11. See frost dates and warnings for what that means in practice. Every year is different, so use this calendar together with the forecast.

❄ January

The garden is asleep, but the gardener doesn’t have to be.

• Read the seed catalogues. This is the best part of a prairie winter. Look for short-season varieties: tomatoes, corn and melons with a short “days to maturity”, and perennials rated for Canadian zone 4 or colder. See growing degree days for why the packet’s days may stretch here.
• Plan the beds. Sketch last year’s garden and move crop families to a new spot this year (tomatoes and potatoes in one group, the cabbage family in another) to help keep soil diseases and pests from building up.
• Water evergreens during a long chinook. If a chinook keeps it mild for several days and the ground isn’t frozen, give spruce, pine, juniper and cedar a drink around midday so it can soak in before the night freeze. This helps prevent winter burn, the browning on the south and west sides in spring.
• Check stored bulbs and produce. Look over dahlia tubers, gladiolus corms, squash, potatoes and onions. Toss anything soft or mouldy before it spreads.

❄ February

• Order seeds early. Popular varieties sell out. Check what you saved last year with a quick germination test: roll ten seeds in a damp paper towel, keep it warm, and count how many sprout in a week or two.
• Set up seed-starting gear. Wash trays, check the lights and timers, and buy fresh seed-starting mix.
• Start onions and leeks from seed in the last week of February or early March. They’re slow, and need 10 to 12 weeks indoors. See starting seeds indoors.
• Prune elms only until March 31. Alberta bans elm pruning from April 1 to September 30 to protect against Dutch elm disease, because the beetles that spread it are drawn to fresh cuts.
• Keep watering evergreens in chinooks, as in January.

🌱 March

• Early March: start petunias, lobelia, snapdragons and celery indoors. Finish starting onions and leeks.
• Mid- to late March: start peppers and eggplant. They need warmth to sprout, about 24 to 29°C, and 8 to 10 weeks indoors.
• Prune fruit trees and most shrubs while they’re still dormant, before the buds swell: apples, crabapples, plums, cherries, and summer-flowering shrubs. Leave spring-flowering shrubs like lilac until right after they bloom, or you’ll cut off this year’s flowers.
• Last chance for elms: the pruning ban starts April 1.
• Don’t uncover the garden yet. March and April can still bring heavy, wet snow, and a sunny week can be followed by a deep freeze. Leave mulch on perennial beds.

🌱 April

• Early April: start tomatoes, and broccoli, cabbage and cauliflower, indoors. Six to eight weeks is plenty for tomatoes.
• Mid-April: start marigolds, zinnias and cosmos.
• Go to Seedy Saturday. Environment Lethbridge holds this free seed swap with workshops at the downtown library, usually in early April. Bring extra seeds to share.
• Take off tree wraps from young trees once the weather settles, so the bark doesn’t stay damp and insects can’t shelter underneath.
• Hold off on the big cleanup. Many helpful insects, including native bees, spend the winter in hollow stems and leaf litter. Wait until days are reliably warm before cutting back old perennial stems, and then cut and leave short pieces in the bed.
• Late April, if the soil is ready: sow peas, spinach, lettuce, radishes, onion sets, carrots, beets, parsnips, Swiss chard and sweet peas. Do the squeeze test first: if a handful of soil forms a sticky ball, wait.
• Rake the lawn lightly and aerate compacted areas.

🌼 May

• Early May: start cucumbers, squash, zucchini, pumpkins and melons indoors in pots, three to four weeks before planting out. Keep sowing hardy crops outdoors.
• Early to mid-May: plant seed potatoes, onion transplants, kale and turnips. Plant hardened-off broccoli, cabbage and cauliflower transplants around mid-May.
• Harden off seedlings over 7 to 14 days before planting them out. In Lethbridge, wind is as big a shock to a seedling as sun.
• Don’t trust the May long weekend. It’s a tradition, but it’s often too early for tender plants here.
• From about May 25 to June 1: plant out tomatoes and frost-tender bedding annuals, with old sheets or frost cloth ready for cold nights.
• Divide crowded perennials as they start to grow.

☀ June

• Early June: plant peppers, eggplant, melons, cucumbers and squash, and sow beans and corn, once nights stay above about 10°C and the soil has warmed.
• Mulch vegetable beds once the soil is warm, and keep mulch topped up on perennial and shrub beds.
• Thin carrots, beets and lettuce so they have room to grow. Eat the thinnings.
• Hoe weekly. June is when weeds sprout fastest; ten minutes a week now saves hours later. See natural weed control.
• Stake tomatoes and tall flowers before the wind does it for you.
• Hail season starts. From June through August, keep a tarp, old sheet or shade cloth handy for stormy afternoons. Many plants recover better than they first look; give them a week before you pull anything.
• Prune lilacs and other spring-flowering shrubs right after they finish blooming.

☀ July

• Water deeply, in the morning. July is usually hot, dry and windy. Aim for about 2.5 cm a week from rain and watering together, and more in a hot, windy week. Pots may need water every day. See soil, compost and watering.
• Harvest often: peas, lettuce, zucchini, beans and herbs all produce more if you keep picking.
• Snap off garlic scapes, the curly flower stalks on hardneck garlic, so the plant puts its energy into the bulb. They’re delicious.
• Last small sowings by mid-July: lettuce, radishes and spinach for a fall crop.
• Watch for hail and cover what you can on stormy afternoons.
• Solarize a weedy patch for next year, under clear plastic during the hottest weeks.

🍅 August

• Peak harvest. Tomatoes, corn, beans, cucumbers, early potatoes. Share the extra zucchini.
• Lift garlic when about the lower third of the leaves have yellowed and died back, usually late July or August. Cure the bulbs in a dry, airy, shady spot for a few weeks.
• Stop fertilizing shrubs, trees and perennials. Late feeding pushes soft new growth that won’t be ready for winter.
• Save seeds from open-pollinated beans, peas, lettuce and flowers. Let them dry fully on the plant.
• Help tomatoes finish. In the second half of August, pinch off new flowers and small fruit that won’t have time to ripen.
• Keep watching for hail into late August.

🍂 September

• First frost: about a one-in-three chance it arrives before September 11. Watch for clear, calm nights. Cover tender plants on the first cold nights; there are often two or three warm weeks after.
• Before a hard frost, pick every tomato showing colour and the full-sized green ones, harvest squash and pumpkins with a few centimetres of stem, and pick peppers and beans.
• Dig potatoes once the tops have died back, on a dry day. Let them dry on the surface for a few hours before storing.
• Plant spring bulbs like tulips, daffodils, crocus and scilla from late September into October.
• Plant garlic starting in late September. See October.
• Bring houseplants back indoors before the first frost; check them for insects first.
• Leave kale, carrots, parsnips, Brussels sprouts and leeks in the ground. They taste sweeter after frost.

🍂 October

• Plant garlic. Late September to early October is the usual window here, and a little later is fine in a long, mild fall as long as the cloves go in a few weeks before the ground freezes. Plant cloves 5 to 10 cm deep, pointed end up, and cover with 10 to 15 cm of straw or leaves. Garlic needs good snow cover or mulch to get through the winter.
• Dig gladiolus and dahlias after the first frost blackens the leaves. Dry them off and store them somewhere cool and frost-free.
• Deep-water evergreens and young trees before freeze-up, so they go into winter well soaked. This is the best defence against winter burn.
• Wrap young trees with light-coloured tree guards, to protect thin bark from sunscald on bright winter days. Leave them on until spring.
• Do a gentle fall cleanup. Remove diseased plants and seedy weeds. Leave some perennial stems and seed heads standing: they shelter insects over winter, feed birds, and catch snow, which insulates the roots below.
• Shred fallen leaves with the mower and use them as mulch or save them for the compost.
• Elm pruning season opens on October 1.
• Drain and store hoses, rain barrels and timers before the first hard freeze.

❄ November

• Mulch perennial beds after the ground freezes, not before. The goal is to keep the ground frozen through chinook thaws, so plants aren’t heaved out of the soil by freezing and thawing.
• Clean, sharpen and oil tools before putting them away.
• Write down what worked. Which varieties did well, when the first frost came, where the hail hit. Next January, you’ll be glad you did.
• Water evergreens during any long mild spell if the ground is still open.

❄ December

• Rest. You’ve earned it.
• Brush heavy, wet snow off shrubs and young trees gently with a broom, upward, to keep branches from breaking. Leave ice to melt on its own.
• Pile clean snow on garden beds and around shrubs. It insulates roots and soaks in when it melts. Keep salty snow from the street and sidewalk away from plants.
• Care for houseplants. Short days and dry furnace air are hard on them; water less, and group them together for humidity.
• Give the gift of gardening: seeds, a good pair of gloves, or a sharp hoe.

A kid’s job for every season

Sources

• Environment and Climate Change Canada, Canadian Climate Normals 1981–2010, Lethbridge CDA, frost probabilities.
• Government of Alberta, “Dutch elm disease prevention: what you can do” (annual elm pruning ban, April 1 to September 30).
• University of Saskatchewan, Gardening at USask, garlic growing guide (planting depth, mulch, harvest timing).
• Alberta Agriculture, “Garlic: fall vs spring planting” FAQ (planting relative to first fall frost, snow cover and straw mulch).
• CTV News Calgary, “Seedy Saturday event returns to Lethbridge this weekend”, April 2025 (Environment Lethbridge).
• Seed-starting timings as on this site’s Starting seeds indoors page.