The Garden Centers Say Go, The Weather Says Wait
- Diana Pierce
- May 6
- 6 min read
By Diana Pierce | May 06, 2026
I visited a big box garden center recently and stopped cold.
The shelves in the back of the garden area were jam-packed with plants, still in their shipping wraps. An employee told me more were arriving every day.
Here’s what most shoppers don’t know: those plants were grown in warm-climate greenhouses and shipped north on a corporate timetable — not a Minnesota one. They’ve already been stressed by the journey before they ever reach your cart.
That’s not true of locally grown plants from places like Bachman’s or Gertens, where what’s on the bench was grown here, for here. But at the big box stores, the calendar says spring long before Minnesota does.
Our temperatures are still dipping into the 30s at night. The garden centers are saying go. The weather is saying wait.
It’s a familiar Minnesota tension. And it’s exactly why I called Laura Irish-Hanson, horticulture educator with University of Minnesota Extension.
Frost Dates and Safe Planting Windows
Diana: What’s the general rule of thumb when it comes to when it’s safe to get into the soil in spring? How does that timeline shift across zones 3 through 5a?
Laura: The term most gardeners hear is “last frost date” — in the Twin Cities and southern Minnesota, that typically falls in the last week of April. But what that actually means is when we’ll hit a hard freeze at 28 degrees Fahrenheit, which is far too cold for most annual plants. Most annuals need nighttime temperatures of at least 50 degrees minimum. The last frost date is just one data point, not a green light to plant.
The Minnesota DNR has excellent frost probability tables — search “last frost date Minnesota DNR” — where you can select the location closest to you.
Diana note:
When I did a search, based on where I live in the Twin Cities, here’s what I learned:
Safe Planting: By May 21–23, there is a 90% probability that temperatures will stay above 36°F, making it safe for most sensitive plants.
Laura: I recommend erring toward caution and looking at the 10 to 20 percent probability range for nights that drop below 36 degrees. That tells you there’s a 10 to 20 percent chance a night after that date will still dip below 36. Those same tables show growing degree days and growing season length by location, which helps enormously with cultivar selection.
Diana: What about readers in Colorado or Canada who follow this newsletter for cold-weather guidance?
Laura: Colorado readers can use those same Minnesota DNR tables as a reference — I’d suggest looking at the Northwest corner of the state, since it tends to be drier, similar to Colorado conditions.
Soil Temperature: The Other Number That Matters
Diana: Soil temperature seems to matter as much as the calendar date. How do gardeners check that?
Laura: The Minnesota DNR also has an interactive soil temperature tool with readings tracked across the state at multiple depths — generally two to six inches.
Skip sticking your meat thermometer into the ground; it won’t measure low enough. The more important caution is to avoid working in wet soils. Spring brings heavy precipitation and compacting wet soils by walking or digging does lasting damage. Once the maps show soil temperatures above 40 degrees, cool-season plants like snapdragons, lettuce, and radishes are safe. Warm-season plants — tomatoes, peppers, zinnias — need soil above 60 degrees. Cucumbers and squash want it above 70 to germinate well.
Here’s a link to soil temps across the United States. Just put your city in with a zip code, and it will display what the last month’s soil temps were.
Diana note:
I live in the Maple Grove/Plymouth, Minnesota area so last week, using that link, my local soil temp registered at 60 degrees.
The Eagerness Problem: Starting Too Early
Diana: What are the most common mistakes Minnesota gardeners make when they’re eager to get started too soon?
Laura: Starting seeds indoors too early is the big one. Plants that have been growing indoors too long need to be potted up multiple times — more space, more potting mix, more water, more cost. But the real problem is transplant shock. Larger plants struggle more when they finally go into the ground. You want seedlings with about four sets of true leaves, generally under six inches tall. Those big leggy tomatoes going into hard transplant shock is completely avoidable. Putting plants outside too soon creates another problem that’s not always obvious immediately. If peppers experience temperatures below 50 degrees, it can inhibit their ability to flower and fruit — but you won’t see that damage until months later.
Pro Tip - A Note on Leggy Tomatoes
Laura: If your tomatoes got leggy, there’s a fix. Tomatoes have latent root initials — dormant roots in their stems — so you can bury them deep. An 18-inch tomato can go into the ground with the first foot buried underground, all leaves removed. The stem will root out. You can even bury them sideways. If a windstorm snaps a stem, you can root that cutting in a glass of water and once the white root nubs are just under an inch long, transplant it into the garden. One tomato becomes two.
What Can Go Out Now, and What’s Still Safe to Start Indoors
Laura: Cool-season plants are fine outside right now in early May — pansies, snapdragons, ornamental kale. They don’t generally need covering unless it drops below freezing. Spring bulbs — tulips, daffodils — can handle it down to about 31 or 30 degrees before the flowers take damage; a light cover helps.
For warm-season plants, I hold off until closer to Memorial Day in the Twin Cities. Smaller transplants, less babying, less risk. For seeds, I recently sowed zinnias, sunflowers, and squash. Tomatoes and basil went in just a week before. If you’re in northern Minnesota, now is the time to start tomatoes and tomatillos — you’re not too late, whatever your neighbors started in February.
Fall brassicas like cabbage I won’t start until late June, for transplanting out in August.
Prepping Containers Before You Plant
Diana: What should container growers be doing right now to prep before they plant?
Laura: For containers 10 inches or larger in diameter, refresh at least 50 percent of the potting mix. Container mix breaks down quickly from frequent watering — the particles shrink and roots lose access to the oxygen they need.
I dump mine into a wheelbarrow to incorporate and mix rather than dumping on the ground. If you’ve used the same mix for several years, start fresh completely. The old mix can go into in-ground raised beds or compost as “browns.”
If you had diseased plants in a container last year, remove all the old mix and sanitize the container — a one-to-nine bleach-to-water ratio, or 70 percent alcohol. I lean toward alcohol for most containers because bleach can affect porous materials.
Always check drainage holes in your containers. Decorative pots without holes will fill with water and kill plants. A piece of broken terracotta over the hole can help keep fine potting mix from plugging it. For those who want to move containers in and out when frost threatens, a caster wheel system makes that much less of a project.
Diana note: I don’t have a wheelbarrow. I’ll use my wagon instead but I’ll put down plastic bags to protect the bottom and sides.
Soil Amendments for In-Ground Beds
Laura: Only amend soil if it’s actually necessary — amendments are expensive and time-consuming. Get a soil test first. The University of Minnesota Soil Testing Lab does a yard and garden test for $22. It tells you pH, available nutrients, and gives you fertilizer recommendations specific to your situation. Do it every three to five years. If your soil genuinely needs help — I grow in pure sand, so I add organic matter each spring — compost, leaf litter, and mulch are your tools. Clay soil also benefits from organic matter to improve drainage. For acid-loving plants like blueberries or azaleas, follow the instructions on any pH-adjusting fertilizer carefully.
Fertilizing at Transplant Time
Diana: Should gardeners be mixing fertilizer into the soil at transplanting, or going with liquid feed?
Laura: Either approach works — some gardeners prefer liquid fertilizer on a hose-end feeder, others use slow-release granular for more control. Right now, garlic and rhubarb are in heavy active growth and nitrogen-hungry. This is a good moment to feed them. Whatever you use, read the label and don’t over apply. Excess nutrients running off into waterways is an ongoing problem in this region.
Next week, Laura turns her attention from the garden bed to local plant sales. County Master Gardener and garden club sales are opening across Minnesota, and she has strong opinions about how to shop them well — including what to look for, what to avoid, and why you should never, ever let go of your wagon.
Have a question for Laura? Hit reply — I’ll make sure she receives it.
Diana
© 2026 Diana Pierce
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