Here in northern Vermont, our first fall frost can come anytime from the end of September through the middle of October, typically. It’s a short growing season, so, like many northern growers we’re interested in how to tease a little more yield out of the field.
There are several strategies for winter growing. You can plant in the field and then provide the crops some protection, you can plant in an unheated tunnel or you can plant in a heated tunnel, which will encourage more growth from the plants.
Why grow in the winter? You worked hard all summer; why not just put your feet up and read by the fire? Many growers find that in the winter, the market is less saturated, so there is a higher demand for product. With the increasing interest in local food, there is a lot of enthusiasm around keeping markets and larders stocked with local produce, even in the winter. Also, winter growing allows farmers to keep employees through the “off season” and have a steady work-load year-round.
Timing Your Plantings
The key to winter harvests is to plant early enough to mature your crop before the cold temperatures and low-light conditions of the winter months essentially halt the growth process of your plants. When the day-length is less than 10 hours, plants go dormant and don’t put on any growth. But if you’ve selected crops that can withstand cold temperatures and you’ve provided adequate cover, they’ll just hang out and wait for you to harvest them.
For us, that generally means seeding direct seeded crops like spinach or lettuce by mid-September. In 2011, we direct seeded spinach in late September, then again the first week of October. This difference of one week seeding time didn’t ultimately seem to have much of an impact; the varieties seeded in early October caught up. Both plantings were ready to harvest shortly before Christmas.
A few of the varieties we seeded in late September had poor germination, and it wasn’t until mid-October that we realized the problem and got around to reseeding. These varieties, seeded by hand in mid-October, did not mature and did not catch up to the earlier plantings, so the difference between an early October and a mid-October seeding date seemed substantial – at least it was that fall.
We experienced this first hand, but Eliot Coleman has a great chart in The Winter Harvest Handbook to save you a little bit of the trial and error. The chart shows that a crop with 40 days to maturity, planted on September 19 would be ready for harvest about 70 days later, on November 25. But that same crop, planted on October 17, would take 110 days to mature, not ready until February 3.
Maintaining the Crop
Once the spinach gets established, we usually weed once or twice before the weather turns cold. Once that happens, the weeds pressure drops way off. We’ve found that irrigation isn’t necessary. The cool temperatures help retain moisture in the soil, the plants don’t grow as fast or draw as much moisture from the soil, and condensation in the air keeps things generally moist. In 2011, because we had a dry, mild winter, we found that we had to begin irrigating pretty early in the spring – late February on – which hadn’t been the case the previous year, and turned into a pretty big pain involving thawing out hydrants and dragging frozen hoses. Irrigation is a good thing to think about and plan for when you’re setting up your high tunnel.
We cover the beds with wire hoops and row cover for a second layer of protection/insulation starting when the outside temperatures drop to around 25º F. When we want to harvest or uncover the beds for venting, we walk down one side of the bed, picking up the edge of the row cover and tossing it over the bed into the path on the other side. Once we get to the end of the bed, the entire length of row cover is loosely folded, length-wise, along the bed in the adjacent path. To re-cover the bed, we again walk the length of the empty pathway, this time pulling the edge of the row cover over the bed as we go.
Eliot Coleman puts it well in The Winter Harvest Handbook: “We were not actively battling the cold of winter…[r]ather we were simply maintaining a protected microclimate sufficient for the needs of our hardy plants. It was like the difference between sitting inside by the fire on a cold day and being outside with enough layers of clothes on to keep you comfortable.”
For the past two seasons, we’ve used a double layer of AG-19 (standard weight) row-cover over each bed. This year though, we’re going to experiment with using just one single layer of AG-19. This is because, after rereading parts of The Winter Harvest Handbook, we saw that Eliot Coleman trialed light-weight (85% light transmission) and heavy-weight (50% light transmission) row covers, and found that the crops actually did better under the light-weight fabric because it allowed for more solar gain through greater light transmission, so the temperatures were warmer. Presumably, with our double layer of AG-19, the light transmission would be about 70%, so better than the heavy-weight row cover, but still might inhibit warming. In late February to mid-March we start watching for overheating under the row cover and removing it during the day on warm or sunny days.
In both years, we got one spinach harvest before Christmas (in early November for the 2010 mid-September seeding date and mid/late December for the 2011 late September-early October seeding date), and no harvest again until February. In our region of northern Vermont, early February is when the day length extends to over 10 hours and plants begin to emerge from their semi-dormancy. But you can see that the earlier seeding date resulted in two earlier harvests, each by two to three weeks, which is significant.
|Year||Seeding Date||1st Harvest||2nd Harvest||3rd Harvest|
By the time of the third harvest, in mid-March, the plantings had pretty much caught up with each other. From mid-March through early May, the regrowth is steady enough to harvest about every 10 days.
We choose to harvest leaves individually because we’ve found that when we clear-cut the planting the regrowth is so much rougher.
Where to Get More Info
To help you determine day-lengths for your area, and when the day-length drops below ten hours:
If you want to build a high tunnel, or looking for more resources about growing in them:
- Constructing a Simple home-scale PVC High Tunnel for under $500 (won’t withstand snow load though)
Useful information, links and articles regarding high tunnel vegetable production:
- High Tunnels is a great manual from the University of Vermont: http://www.uvm.edu/~susagctr/Documents/HighTunnels.pdf