When is it safe to plant seedlings outdoors?

Here's how to avoid getting burned by a late frost

Hello, friends!

‘Miss Kim’ lilacs spilling over the fence into the driveway. With the windows open, I can smell them all the way from the house. (Jessica Damiano)

It’s a beautiful weekend here on Long Island, and that means I’m spending a lot of time in the garden. The rhododendron has faded but the irises and alliums have just started blooming, some small species tulips are up and the lilacs are at their peak, perfuming the front yard and driveway. The perennial beds are filling in nicely, too.

In addition to pulling weeds and shoe-horning in some Jacob’s ladder, Mondarda bee balm, Chelone turtlehead and Caryx pensylvanica sedge that I had no business buying because of lack of space, I’m getting my raised beds and Earth Boxes ready to accept my tomatoes, cucuzza squash, yard-long beans and huckleberry seedlings. And I’m paying more attention to the compost pile.

I love the idea of transforming garbage into free mulch and fertilizer. It's a win-win situation when I can save money and keep my eggshells, coffee grinds and weeds out of landfills. Compost is the single best additive available for improving any soil. It improves the water retention of sand, improves the drainage of clay, and adds an incredible amount of nutrients. No wonder gardeners call it black gold.

Next week, I’ll share my recipe and show you how you can make your own. In the meantime, clear a spot in the back of the yard for your pile.

👉👉If you’re enjoying this newsletter, why not share it with a gardening friend? 


💡 If you do one thing this week…

Prune spring-flowering shrubs as soon as they finish blooming. This means, lilacs, rhododendrons, azaleas, etc. If you wait even just a week, you may risk removing buds that are forming to produce next year’s blooms.

For more daily timely tips — 365 of them! — grab one of my gardening calendars before they’re gone.

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📬 Ask Jessica

DEAR JESSICA: When is the best time to plant tomatoes? — Frank Cetta

DEAR FRANK: Probably later than you think. Not only do you need to wait for the danger of frost to pass, but most warm-season vegetables, and tomatoes, in particular, should not be planted outdoors until the soil has warmed to 65-70 degrees.

Contrary to what you might think, planting any earlier will not give your plants a head start; they won’t really grow until the soil warms up. In addition, planting earlier would risk exposing them to a late frost and if that happens, you might lose them. So patience is key.

Tender seedlings often succumb to a late overnight frost, which is defined as temperatures below 36 degrees. Depending on where you live, obviously, the last frost date will vary. In my neck of the woods, on Long Island, there are three horticultural zones, each with its own last frost date. In Nassau County, the danger of frost is considered to have passed in mid-May; in Suffolk County, it’s a week later, and there’s a small sliver of land around the Pine Barrens that has its own little climate that doesn’t see the end of frost threats until a week after that, around the very end of May. Even then, there’s still a 5-10% chance of an unexpected (or even unprecedented) frost, but it’s widely considered safe to plant.

You will find calculators online that will inform you of the average last frost date in your zip code, but don’t confuse the two. The average is just an average — and not the date when it’s safe to set tender seedlings outside, which could be a full month later. Wait until overnight temperatures are consistently 55 or warmer before planting, and remember that container-planted seedlings are even more susceptible to cold than their in-ground counterparts.

👏 Sunday shoutout

Bill Alberigo of Garden City Park wrote to me last month to ask for insight into his non-blooming Easter cactus. This week, he followed up with an update: “A week after I sent you that email, I noticed buds on the plant,” he said. “It must have sensed that the email to you went out.”

Alberigo said his plant started blooming on Friday. I guess it knows who’s boss! (I’m half expecting an onslaught of emails about uncooperative plants, their owners’ hoping the threat alone will scare them into blooming 🥀>>🌼)

📧 Send me your feedback!

I welcome your comments and suggestions, so please send them along — as well as any topics you’d like to see covered and questions you’d like answered in the Ask Jessica section.

Until next week, stay safe. Be well. And always keep your mind in the dirt. —Jessica

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