When to Plant Containers and Raised Beds

Planting time is local. It depends on the plant, recent weather, soil temperature, day length and how exposed the planter or bed is. A date from another region's calendar is a guess; your local frost dates and a soil thermometer are data.

Hardiness zones are not frost dates

Hardiness zones, Canada's and the USDA's, rate how well a plant survives winter. They do not tell you the last spring frost or the first fall frost. Get frost-date probabilities for your area from a weather service or extension office, and remember that an average last-frost date still leaves a real chance of frost after it. Watch the forecast before you plant anything tender.

Containers and raised beds run warmer and drier

Soil above ground warms sooner in spring than the ground around it, which is one reason raised beds can be planted earlier. It also dries faster in sun and wind and cools faster in autumn. Check the soil with a thermometer against the germination temperature on the seed packet, and check moisture with a finger, not a schedule.

A season-by-season plan

Early spring: set up

• Check planters and beds for loose fasteners, damaged finish and blocked drains, and clear leaves and soil from outlets.
• Loosen compacted soil and top it up with compost or fresh mix; replace mix that drains badly or held a diseased crop.
• Test irrigation lines, emitters and timers before relying on them.
• Harden off transplants over a week or two: a few hours outside at first, longer each day.

Spring: cool crops first

Lettuce, spinach, peas, kale and pansies tolerate cool soil and light frost, so they usually go in before the last frost date. Tomatoes, peppers, squash, beans and basil need warm soil and no frost; plant them once the frost risk has passed.

Summer: water and feed

Containers in full sun can need water every day in a heat wave. Group plants with similar needs, mulch the soil surface, and feed container plants regularly, because frequent watering washes nutrients out.

Autumn: second crops and structure

Sow a second round of greens, plant spring bulbs, and leave grasses and seed heads standing for winter interest. Clear spent annuals and top up the soil.

Winter: protect and drain

Evergreens, branches and bark carry a container through winter. Keep drains open so the soil does not sit waterlogged and freeze solid, and keep de-icing salt off planters and plants.

Composing a container

A useful starting point is one upright plant for height, a few mounding plants for mass and trailing plants at the edge. It is a visual rule, not a horticultural one: a single grass or a two-plant pairing can be just as strong. Whatever the mix, pair plants that share light and water needs, leave soil depth for the largest root system, and keep fast growers from smothering slow ones.

Stretch the season

A cold frame is a clear-topped box over a bed. It traps daytime heat and shelters seedlings from wind and light frost, so you can sow earlier in spring and pick greens later into autumn. Open it on sunny days so plants do not overheat, and close it before evening. Our Raised Garden Bed can be ordered with a cold frame kit.

Stock raised beds come in footprints from 2 × 4 ft to 5 × 10 ft and heights of 12, 20 and 26 in. Taller beds mean less bending and more root depth; on wider beds, leave a path on both sides so you can reach the middle.

Keep a record

Note sowing and planting dates, the first and last frosts you actually saw, and what thrived or struggled. After a few seasons your own notes will beat any general calendar.

Planning a new bed or planter: Shop stock sizes.