After the Harvest

Jump start your spring vegetable season

By Jennifer Bousselot:

Growing up on a small family farm I remember how the demands of the crops increase as the season progresses. By harvest time most of our energy seemed to be used up – like we needed the rest and didn’t have any to spare for preparations for spring. Vegetable gardening in Colorado can feel like that too. However, if you have energy to spare this fall, there are a few things that can help jump start your spring vegetable garden season. 

Now is a great time to plant garlic. Photo: Idelle Fisher

Fall Planting 

Garlic is the quintessential fall-planted vegetable crop; few vegetable gardeners would pass up the opportunity to plant a crop that is so universally useful in the kitchen the following summer. 

Ideally, cloves are planted 6-8 weeks before first frost in fall. I’ve gotten away with chipping frozen ground in December to plant garlic for an excellent crop the following July. But learn from my mistakes – don’t wait until then.

Front Range Wild Ones helps host native plant seed swaps each fall.

Other crops can be experimentally grown if sown in the fall, as long as you are able to give them some extra protection over the winter. Over the years I’ve seen growers in Colorado sow carrots, parsnips, and kale in the fall and successfully harvest them relatively early in the spring. The key is to make sure to give them winter protection with a thick layer of straw or floating row covers. 

Another thing that vegetable gardeners can do now is sow Colorado native plant seeds. Most need to go through the temperature fluctuations of winter in order to germinate and grow the next spring. Native plants are great habitat and food sources for insect predators the following summer. Experienced vegetable gardeners know that we need all the insect predator help we can get to control aphids!

Soil Amendments

Our soils in Colorado are notorious for being ill-suited to grow vegetables; they are typically either too clayey or too sandy.  Both types of soil equate to low organic matter and nutrients, especially nitrogen. In general, incorporating up to 3 inches of a high-quality compost 6-12 inches deep is ideal for helping improve soil conditions for growing vegetables. You can send a sample to the CO State University Soil, Water and Plant Testing Laboratory to be sure of your soil texture (i.e. clay or sand) and nutrient levels before adding any amendments. 

Legume cover crops: Vetch and Peas

Cover Crops

One of the simplest ways to simultaneously improve soil conditions, suppress winter annual weeds, and prevent soil erosion is to grow cover crops in your vegetable garden beds and till them into the soil in spring. Many vegetable growers use at least one grass and one legume (plants that have a symbiosis with nitrogen-fixing bacteria in their roots) to balance the many benefits of growing cover crops. 

Examples of grasses are winter wheat or annual rye, which germinate rapidly to anchor soil in place and bulk up quickly to improve organic matter content in the soil when tilled in during the spring. The most common leguminous cover crops are vetches, peas or clovers, which have more lateral growth habits that weave together and cover soil. Legumes also have the benefit of adding nitrogen to the soil, especially when they decompose in the spring after tilling in. Sow winter annual cover crop seeds, per package directions, from mid-September to mid-October in Colorado. Till the green cover crops several inches into the soil in spring before the plants set seed: this practice is called green manuring.

Bindweed is a great weed to remove in the fall.

Weed Management 

Fall is an excellent time to tackle weeds. For perennial weeds such as bindweed and Canada thistle, attacking the plants in fall is ideal as that is when they are moving carbohydrates and nutrients into their overwintering root systems. Use the physiology of the plants to your advantage by applying weed control methods to the top growth of the plants so they will transfer it to the roots quickly.

For annual weed seeds that are in the soil, as well as any plant pathogens, soil solarization can be useful. Typically, a 6-8-week period when the soil is covered in a clear plastic sheet will be effective at controlling the weed seeds and pathogens in the top several inches of soil. Because many of the peskiest perennial weeds (i.e. bindweed, Canada thistle) have deep roots and rhizomes in the soil, they effectively elude the high temperatures that kill the more shallowly positioned seeds and pathogens. See CSU Fact Sheet 0.505 Soil Solarization for more specific details. 

If you can muster even a small amount of extra effort in the fall, it will certainly pay off come spring. 

Jennifer Bousselot is a Green Roof Researcher and Assistant Professor of Horticulture and Landscape Architecture at CSU Fort Collins