Guest Blog provided by UNH Cooperative Extension’s Education Center
For many vegetable gardeners, peak harvest season has passed and we find ourselves 
solemnly imagining how life will be without the option of harvesting fresh produce for our plates daily. Luckily there is still time to try seeding some cool season crops that can handle colder temperatures and actually taste better once cool weather arrives.
To start with, you will want to make sure that your soil is well prepared and free of large soil clods and rocks. Most greens seeds are small and won’t germinate as well in such conditions. While working the soil, apply a balanced fertilizer to ensure that your greens are well-fed throughout remainder of the season.
In certain soils that are very clumpy or tend to form a crust when dry, make a very small trench or depression just 1/8 inch deep. I generally use a board turned with a corner pointed down and press lightly to make the depression. The end of a hoe handle can also be used to mark out the row and leave the shallow trench. Seeding into this trench and covering with a fine seed starting mix or compost will ensure that germinating seedlings can easily push up through the soil surface. Another good technique for sowing greens mixes is to simply take a metal garden rake, the one with the thick metal teeth, and rake one direction across the bed down the entire length. Do this only to a depth appropriate for the crops you are sowing, often only ¼ inch deep. This will make several of the shallow planting trenches to hold your seeds. Then broadcast your mix across the entire bed, scattering the seeds so that you have one land every inch or so. Next, simply rake very lightly across the bed again, but this time rake perpendicular to the direction you raked before. This will cover the majority of your greens seeds with enough soil for good germination. That’s it. Water sufficiently to moisten the top inch of soil and seeding is complete.
Once your greens are seeded, they absolutely must remain moist during the germination and establishment period. A watering wand with a gentle shower setting is a good choice to avoid washing soil and seeds out of the rows while watering. The first two weeks from seeding through germination, emergence and early growth are critical where adequate moisture is concerned. Thin seedlings as needed and keep weeds under control, especially early on as the greens become established.
What type of greens can be grown during the late summer, fall and into winter?
A basic mesclun, or salad mix is a great choice. If you like a bit of a spicy bite in your mix, consider sowing mustards, arugula, mizuna and tatsoi. You can purchase pre-made mixes or create your own custom tailored to your own taste preferences.
Some crops are hardier than others or simply quicker to grow to a harvestable size. The most reliable group includes spinach, baby kale, tatsoi and claytonia. Next would be arugula, mizuna, cress and pac choi, followed by baby lettuces, baby Swiss chard and radishes.
Planting calendars for winter harvest of these crops are available online, and the best of them take into consideration the effect that shorter days have on plant growth rates. All of the crops listed in this article can be grown under protective covering such as a small hoop structure when seeded as late as the third full week in September, while the hardiest options like spinach, baby kale tatsoi and claytonia could be seeded up until mid-October. Of course, gardeners farther north would need to plant on the early side for best results.
One of the great things about growing greens late in the season is that many of the pest and disease pressures that we deal with early in the season begin to lighten up. Additionally, the sunny days and cool night temperatures result in higher sugar levels in the plants, which means great flavor on the plate.
Protect Your Plantings
To really get the most out of your planting, you’ll need to use floating row covers to help protect your greens from cold temperatures, drying winds and early frosts. This lightweight spun-bonded fabric allows light, water and air to pass through it, but offers a few degrees of frost protection that could result in a substantially extended harvest season.
Floating row covers get their name because they are actually used by some growers by just pulling them over the plants and allowing them to “float” or rest on top. During heavy frosts, the plants can still get burnt where they are in contact with the fabric. To remedy this, use heavy gauge wire, pvc piping, or even metal conduit bent into the shape of an arch and placed every 4 to 5 feet down the bed. Essentially, you are making a tiny hoop house with a protected microclimate inside. Consider using the heavier weight row covers, which are measured in ounces per square yard. Clear plastic can also be used for this purpose, but much greater care should be taken in managing ventilation to avoid buildup of excess heat and humidity. Adding a layer of clear plastic over the row cover after a few heavy frosts will provide additional protection and extend the harvest further yet. Experimenting with seeding dates, crop mixes and season extension techniques can result is harvest well in to the fall and winter.