Frost Seeding

March 15, 2019

“It feels like spring.” That’s what my 3 year-old said when we walked outside at 8 AM this morning without winter coats or hats. She was right. And after a winter that started the second week of November with a massive snow storm, an early spring is just what we need.

I walked around the garden yesterday just to get out into the sun and see what was growing. The ground is still wet and fragile, so I stuck to the paths. This is definitely the time of year to appreciate perennial vegetables. Rhubarb and sorrel have already re-emerged. Garlic greens were still a little crumpled, having been flattened so long under heavy wet snow, but the flavor was fresh and vibrant, and I harvested a handful to add to our refried beans.

Gardening in the Unpredictable Spring

Anyone paying attention has noticed that our climate is changing. Especially if you’ve been in the same place for a while. I’ve been gardening in Syracuse for 20 years. When I first started, I used to plan to harvest all the tender annuals–peppers, tomatoes, green beans–by Indigenous People’s Day in mid-October. Now, I can pretty much take it for granted that they can stay in the garden until early November. That’s a huge shift to witness on such a short timeframe. And it’s not just anecdotal, there’s plenty of data to show that on average the first fall frost is coming later around the US. Check out this cool (yet sobering) graph where you can select a city to see the change.

Spring is less predictable. Warm spells in February or March can lure plants (and gardeners) into starting early, but late spring frosts are still common. Plants that bud or flower early, or seedlings set out too early, can suffer significant damage or even be lost for the season.

Besides, snow melt and spring rains often leave soil too wet to work until April. So, what can you do to get in an earlier spring planting?

Try Frost Seeding

Frost seeding is a practice that’s generally more familiar to small farmers than to home gardeners, but we can take advantage of it too! Basically, it works like this: seeds need good soil contact to germinate. Usually gardeners make that happen by planting seeds in a hole or furrow in the soil and gently tamping the soil to cover, or by broadcasting seed and raking it in. But using those methods in wet soil just leads to compaction and degrades soil structure, possibly for the entire growing season.

With frost seeding, you take advantage of the natural freeze-thaw cycle in late winter/early spring. The water in the soil freezes as temperatures dip below freezing overnight and then thaws as temperatures warm during the day. This is what causes soil to heave. It’s often the source of problems for gardeners and homeowners–cracking foundations and heaving posts out of the ground–but we can also use this natural process to plant our seeds for us. As the soil shifts up and down, it slowly draws the seed down, creating the necessary seed to soil contact.

All you need to do is broadcast the right seed at the right time.

The ideal timing for frost seeding is when there are still several frosts left. Plant too early, and seed is more vulnerable to rotting before conditions are right for germination. Wait too long, and you won’t be able to take advantage of the freeze-thaw action to draw your seeds into the soil. If you choose the right seeds and plant at the right time, they’ll survive just fine through many freezes, and even a late March snow storm.

A perfect strategy for a typical Syracuse spring!

Choosing a Crop 

There aren’t many crops that can be seeded in this way. Clover is commonly frost seeded by farmers in the Northeast, and I’ve successfully frost seeded garden paths to clover even during a January thaw. You need to choose seed that can germinate in colder soil temperatures, isn’t prone to rot in wet soils, and can be broadcast–you’re not going to successfully frost seed peppers.

The two vegetable crops I’ve tried frost seeding are arugula and spinach. Spinach will germinate at temperatures as low as 38F. Both benefit from an early spring planting, because they’re prone to bolt prematurely in hot weather. So, a late April planting can bolt before you’ve even had the chance to get a decent harvest when May temperatures soar into the 80’s.

Last year, we weren’t able to turn our garden beds until April 23, a full 2 weeks later than any previous year. But, we had a warm spell in January. And we had a couple large packs of old arugula and spinach seed. So, I frost seeded both in January.

The spinach germinated ok, but the arugula was not as good. I broadcast a second seeding of both in early April, which did much better. In the end we had our best spinach crop ever and one of our best arugula crops, producing well into June. I’m trying it again this year with fresh seed and a mid-March planting to see if germination improves.

I used to try to sow a late fall planting of greens to winter over, but sometimes fall is just to busy with food preservation and putting everything to bed for the season. In March, there aren’t a lot of other garden tasks competing for attention, and after a long winter, most of us are eager to get started.

Planting the Seed

To take advantage of frost seeding, you need to have a space in your garden that’s ready for planting — bare soil that’s reasonably smooth and level (not covered with weeds or crop residue or thick mulch, unless it’s easily removed, but an inch or two of snow is ok). You’ll use more seed in broadcasting than you would if you were carefully planting a row. For spinach, I use about 3/4 of an ounce (about 1500 seeds) for 50 square feet. Typical seed packets vary, but are likely to be 1/4-1/2 ounce. There are a lot of great companies with dozens of varieties to choose from, but just to give an example, we get a large 1 oz packet of Giant Winter spinach from Fedco for $3.80. For arugula, try 1/8 oz for 50 square feet.

Once you have your seeds, mark your planting area and broadcast the seed being careful not to step on your planting soil. If you’re new to broadcasting seed, an easy way to spread it evenly is to divide the seed in half, broadcast half of it over the entire area, and then starting from the opposite direction, broadcast the other half over the same area. That way if you start broadcasting and find that you’ve used all your seed before you finish the area, you still have half the seed left to even it out.

You might feel odd, leaving your precious seed exposed to the elements. If you feel compelled to add a little protection, you can sprinkle a light layer of finished compost or mulch over the seeding, but it’s not necessary. Those little seeds are hardier than they look!