The Fall Garden
Cover Crops & Mulching
Investing in Next Year's Garden
As you finish harvesting your summer crop of crispy beans, fragrant herbs and sweet tomatoes, you can turn your energies toward tending the fall garden. A sustainable organic garden is dependent on the health and nutrients in your soil. Our rainy PNW winters tend to leach nutrients out and wash them away. Replenishing your garden soil over the winter months while you are warm and cozy inside is as easy as adding a layer of mulch and/or planting cover crop seeds.
What type of soil do you have?
Sandy soil feels gritty and has large particles. It drains easily, allowing water to move through it quickly. Which, in turn, washes nutrients away during winter rains. Sandy soil requires organic amendments such as an organic fertilizer blend. It also benefits from mulching to help retain moisture.
Heavy clay soil feels lumpy and is sticky when wet & rock hard when dry. The clay holds water and drains very slowly. Waterlogged soil can rot roots of over-wintering plants and drive away beneficial soil organisms. Clay soil is poor at draining and has few air spaces. If the drainage for the soil is enhanced, then plants will develop and grow well, as clay soil can be rich in nutrients.
Loamy soil is an even mix of sand, silt and clay. A handful feels fine-textured and slightly damp. This soil has ideal characteristics for gardening and is easily cultivated. It warms up quickly in spring, but doesn't dry out quickly in summer. Loamy soils require replenishing with organic matter regularly, and tends to be acidic.
Additional Soil Resources
If you live locally in King County, Washington state you can get a free soil test from the King Conservation District. They test for Nitrogen, Phosphate, Potassium, Magnesium, Calcium, Sodium, Sulfur, Organic Matter, pH, and Cation Exchange Capacity. The laboratory will analyze your soils and provide recommendations specific to your plant needs.
Soil Questions & Info:
The Tilth Alliance has soil and gardening information. You can email them or reach them on their hotline.
Cover Crops vs. Mulching
No matter your soil type, cover crops will help by feeding the microorganisms in your soil and protect the nutrients from being washed away by winter rains. You can find a variety of cover crop seed at Molbak's.
Mulch, a layer of material spread on top of the soil, can be anything from compost to straw. Mulching can keep weeds down, protect beneficial soil organisms, and add valuable organic matter.
Choosing a cover crop
In sandy gardens, plant a winter wheat or rye. The fine roots help hold nutrients in the soil. In the spring till or turn the garden over with a shovel to build the soil.
Those with clay soil can use a clover to break up the soil or legumes, which tap roots loosen compacted soil and bring valuable nutrients up from the sub-soil.
When in doubt, use Crimson Clover or choose a 3-way blend, which includes a cold hardy mix of seeds good for all soil types; designed for our Northwest winters.
In the vegetable garden
After a harvest, many gardeners plant a cover crop or "green manure" crop such as legumes, clover, or a combination of rye, vetch and clover. Cover crops fix nitrogen in the soil while building texture, improving aeration and drainage, as well as adding organic matter.
Bonus: Planting a cover crop also keeps out the weeds over the winter. Cover crops are tilled in before they go to seed (or simply turned with a shovel), and break down quickly so a new harvestable crop can be planted right away.
Over-wintering vegetable, perennials, shrubs and garden beds slated for early spring planting are all good candidates for mulching.
Add 6-12″ of mulch over any empty garden beds. When you are ready to plant in the spring, turn the mulch and soil together and plant!
Trees & Shrubs
Mulching around trees and shrubs protects roots from severe cold.
Layer mulch 3-4" deep around shrub where you estimate the roots to be. For the health of your shrubs, keep a 3-4" ring around the base of any woody trunk free of mulch.
No matter which method you choose, a little work now can make a big difference in the health and productivity of your garden next year. So take advantage of the cooler autumn afternoons and do a little mulching and cover cropping!