US + Canada

Milk Jugs in the Snow: A Beginner's Guide to Winter Sowing

Put seeds in a milk jug, abandon it in a snowbank, call it gardening. It works. Annoyingly well.

A cartoon farmer in a straw hat sits on a snowy porch surrounded by milk-jug mini greenhouses full of seedlings, while a hen in sunglasses watches from a stack of trays

Apparently you can put seeds in an old milk jug, abandon it outside in the snow, and call it gardening. Meanwhile, half of us have a basement humming with grow lights, heat mats and a fan, like we're running a very suspicious, very small agricultural operation.

Turns out the milk-jug people are onto something. It's called winter sowing: the jug acts as a tiny greenhouse, winter's freeze-thaw cycles do the work a fridge would, and in spring the seedlings come up already tough enough for real weather. No lights. Less fuss before transplanting. Barely any effort, which is the best kind.

Here's how to do it, when to start where you live (US and Canada), and which seeds love it versus which will just sit there sulking.

What winter sowing is

You sow seeds into vented, clear containers (milk jugs, pop bottles, salad clamshells), put them outside, and let the winter do the work. SDSU Extension describes it as a way to start seeds "as early as December or January," and notes it's often used for seeds that need cold stratification, a stretch of cold and moisture that softens the seed coat and breaks dormancy [1]. The technique was originally developed by Trudi Davidoff on her Winter Sown website [1]. It's cheap, uses recycled materials, produces lots of seedlings, and needs no indoor space or grow lights [1].

The seeds also get a natural cycle of cold, warm and wet, and stay protected from being washed away or eaten by bugs and birds [1].

What to sow (and what to leave alone)

SDSU's list of good candidates [1]: - Native plants that need cold stratification (the packet may carry a code: "C30" means at least 30 days of stratification) - Perennial flowers and annuals that self-sow or are cold tolerant - Alliums - Frost-tolerant greens such as spinach and some lettuces - Self-sowing herbs: dill, cilantro/coriander, fennel

Leave the tomatoes alone. For South Dakota, SDSU says not to winter sow heat-loving crops or those needing warm soil to germinate, such as the nightshade (Solanaceae) and cucurbit families, and warns that many online winter-sowing guides come from much milder zones [1]. Even cold-hardy brassicas germinate better in warm conditions and shouldn't be started outside too early [1]. SDSU's advice is written for a cold-winter state; if your winters are milder, check your own state or provincial Extension/ag ministry before trusting a jug with your peppers.

When

Per SDSU: native perennials December to February, as late as March in colder climates, though germination may suffer if the cold period is too short; cold-hardy annuals, perennials and vegetables February to April depending on climate and seed type [1]. Those windows are South Dakota's. Shift them by your own frost dates (see below): the colder and longer your winter, the more the "as late as March" end applies to you. If your winters are mild, don't borrow a cold-state calendar: ask your state Cooperative Extension office (US) or your provincial agriculture ministry (Canada) when local gardeners start seeds outdoors, and check your frost dates below.

How (the 9-step version, trimmed)

  1. Wash the container with warm soapy water. [1]
  2. Cut around it about 4 inches from the bottom; on a gallon jug leave the handle area uncut as a hinge. [1]
  3. Poke drainage holes in the bottom. [1]
  4. Add 2-4 inches of soilless seed-starting mix and moisten it. [1]
  5. Sow to the depth on the packet; thin soil cover unless the packet says surface-sow or needs light. [1]
  6. Close it up with tape (or zip ties/pipe cleaners) but leave the cap off so moisture gets in. [1]
  7. Label it, noting that some permanent markers won't survive the weather; a tag inside works. Record seed and date. [1]
  8. Put it outside in a sunny, protected spot (a milk crate stops it blowing over). Adding snow inside mimics outdoor conditions. [1]
  9. Transplant at two sets of true leaves or about 2 inches tall. [1]

Reality checks (SDSU's, not ours)

Your zone vs. the neighbours' zone (US and Canada side by side)

United States Canada
Official map USDA Plant Hardiness Zone Map, 2023 edition [4] NRCan Plant Hardiness Zones, 1991-2020 (2025 update) [2]
What it measures Average annual extreme minimum winter temperature, 1991-2020 [4] Several climate variables combined into one zone [2]
Scale Zones 1-13, each 10°F wide, split into "a" (colder) and "b" (warmer) half-zones [4] Its own numbered zones; NRCan also publishes a separate USDA-method (extreme minimum) map for Canada [2]
Look yours up ZIP code search at planthardiness.ars.usda.gov [4] Municipality search at planthardiness.gc.ca [2]

Because the two official maps are built differently [4][2], a Canadian "4" and a US "4" are not the same thing. If a catalogue prints USDA zones and you're in Canada, use NRCan's USDA-method map, not the standard Canadian one.

Frost dates beat zones for planning. Zones are about surviving winter; frost dates tell you when to plant. Look up your local average last spring and first fall frost: in the US, NOAA's 1991-2020 U.S. Climate Normals (or your state Extension office) [5]; in Canada, ECCC's Canadian Climate Normals for your nearest station [3]. An average frost date is a 50/50 date, so half of years run later. Your local numbers beat any regional rule of thumb, so look yours up rather than trusting a map in a catalogue.

Next step this week: pick three cold-tolerant seeds from the catalogue you've been hoarding and start one jug. Short on time? Batch it: cut and label all your jugs in one sitting, sow them the same afternoon, and let winter handle the rest. Your main job after that is a glance now and then to make sure nothing has blown over.

Sources