October 27, 2026

When to start planting in raised beds

Start planting in raised beds once a squeezed handful of soil crumbles, and start with hardy crops like peas, spinach, lettuce, and radishes. Hold tomatoes, peppers, squash, and beans until your own yard's last frost has passed. Raised soil warms and drains sooner than ground soil, because it sits above the cold, wet ground and takes sun on its sides. The air above the bed still freezes on the same nights as the rest of your yard. So the frost date decides when tender plants go in.

The published date for our area puts the last frost on April 28. Our station's nightly lows run 7°F below the forecast, and that offset moves our planning date to May 20. The last spring frost we recorded this year came on April 30. We transplanted tomato seedlings into a raised bed on May 18. The steps below take you from an empty bed to a planted one.

Step 1. Find your yard's last frost date

Start with the published last frost date for your area. That date comes from regional records, and your yard can sit warmer or colder than it. On still nights, the denser cold air slides downhill and collects in hollows and low yards. A yard in a hollow can see frost weeks after the published date. Our guide on why your last frost date is probably wrong walks through the causes.

The microclimate checker looks back over recent nights and sets the forecast against readings from home weather stations near you. You get a median and a range for your area, along with a count of the stations behind them.

Step 2. Enter your offset in Siltwell

In Settings, go to Garden, choose Edit garden, and enter a value in Microclimate offset. A negative number means your yard runs colder than the forecast. Siltwell shifts your frost alerts, the forecast lows you see, and the frost dates used for planning by that amount. Frost alerts run for every garden, with or without an offset.

Connect a weather station and Siltwell derives the offset from its outdoor air readings. Once station and forecast lows overlap for about 14 days, Siltwell trusts the learned number. Until then, your manual offset applies.

Step 3. Check that the bed soil is ready

Squeeze a handful of soil from the middle of the bed. If water drips out, wait a few dry days. Working wet soil presses the particles together and closes the pores that roots and air need. Soil that falls apart under a poke is ready to plant. A bed that settled over winter needs topping up first, and our guide to compost for raised beds covers what to add.

Step 4. Sow the hardy crops first

Peas, spinach, lettuce, radishes, onions, and kale can go in before your last frost. These crops tolerate light frost because their cells build up sugars that lower the temperature at which they freeze. A raised bed helps them, since its warmer, drier soil lets seeds germinate sooner.

Sow at the depth on the packet. Small seeds like lettuce go barely below the surface, and large seeds like peas go deeper. A small seed holds little stored energy, so it can't push a shoot through much soil.

Step 5. Lay out the planting chain

A bed rarely holds one crop all season. Spinach bolts as the days warm, and a tomato or bean row can take its place. Siltwell's season plan lays out that chain for a bed. The frost dates it plans against include the offset you entered in step 2, so the chain lines up with your yard. On every account, the bed with the most planned rows shows its full chain. For spacing and layout, see our raised vegetable bed plans.

Step 6. Transplant tender crops after your real last frost

Tomatoes, peppers, squash, cucumbers, and beans go in once your adjusted last frost date has passed and the forecast shows no frost. Each evening Siltwell checks whether tomorrow night or the next will reach your frost threshold, and alerts you if so. Set tomatoes deeper than they sat in the pot. The buried stem grows roots, which gives the plant more reach into the bed. Our guide on planting out tomatoes by your real last frost covers the timing in detail.

What can go wrong

• A late cold night. If a frost alert arrives after planting, cover tender plants before sunset. Our guide on when to cover plants with frost cloth explains why the timing matters.
• A bed that dries fast. Raised beds drain freely, so the top layer where young roots sit dries first. New transplants feel it within days of a dry spell.
• Soil that slumps. Fresh fill settles as air pockets close and organic matter breaks down. Top it up before sowing so seedlings sit near the rim.

Our ground bed ranged from 32% to 62% moisture between mid-July and early September, while raised bed 1 stayed inside a band of 39% to 54%. Raised bed 3 swung across the same range as the ground bed, so a raised frame alone doesn't steady moisture. When both of a probe's two most recent readings fall under 25%, Siltwell warns you about the bed that probe is mapped to. The alert names the bed, and you do the watering. Our guide to watering raised beds for vegetables goes further.

Your offset describes night air temperature. It can't tell you how warm the bed's soil is at seed depth, and bean and squash seeds can rot in cold soil after frost risk ends. They soak up water but germinate slowly, which gives soil fungi time to attack.

If you don't know your offset yet, run the microclimate checker and enter its median as a starting point. After your first few cold nights, compare a thermometer at bed height with the forecast low and adjust the number.