One can add fertilizers to improve plant growth, but we prefer to improve and build garden soil holistically. Most commercial fertilizers boost levels of nitrogen, phosphorus, and potassium, which are the main nutrients plants need to grow. However, there are soil structures and symbiotic relationships with bacteria and fungi that benefit the growth of food crops. We envision ideal garden soil that contains nutrients required for plant growth and conditions for regenerating those nutrients. We try building soil rich in organic matter, crawling with worms and other invertebrates, and teeming with microbial life including beneficial bacteria and fungi. The practices we recommend come from organic, permaculture, and no-till traditions.
“Rules” of Thumb
1. Don’t disturb the soil unnecessarily. This helps preserve soil structure and maintain active microbial life.
- Use garden forks and broad forks instead of machine tillers. Rototillers chop up beneficial soil fungi and, with repeated use, can create a hard pan (layer of soil that water and roots do not easily penetrate).
- When cleaning up garden beds to re-plant, leave what old annual plant material you can, cutting large plants at ground level instead of pulling up by the roots. (Weeds still need to be pulled by roots or dug out.)
- Weed seeds germinate when they detect light. If the seeds remain buried, thanks to no-till / no-dig methods, there are fewer weeds.
2. Cover bare soil. This practice adds organic material, reduces erosion, discourages weeds, moderates soil temperature and helps maintain soil moisture.
- Plant cover crops in unused beds
- Peas & oat cover crop – Use 70% peas and 30% oats by weight with a bacterial inoculant to facilitate nitrogen fixation. This seed mix can be planted before mid-September as a fall cover crop. Peas and oats will not survive the winter here. These plants will be mostly decomposed by spring, so you can plant directly into what’s left of the cover crop. Alternatively, peas and oats can be planted as soon as soil can be worked (usually early March) or as late as April in beds that won’t be used until late May or early June. These are cold-tolerant plants that will grow when many weeds cannot. They create a dense mat of vegetation that smothers weeds. When it is time to plant the main crop, pull or cut the cover crop and leave it on the bed. Ideally, this is done just before the peas and oats make seeds. You will have improved the soil and grown mulch right in the place you need it.
- There are many cover crops to choose from. When making a selection, think about timing and ease of termination (killing the cover crop). Hairy vetch and winter rye, for example, make large amounts of biomass in the fall and into the spring, but winter rye takes some effort to kill prior to planting the main crop. It can be terminated by cutting or flattening as it starts to flower, then covering the bed with a tarp for about 2 weeks.
- Use succession planting to keep beds in use
- The same bed can be used for spinach in March to May and tomatoes, peppers or eggplants starting in June. Depending on the food crop, it may be possible to grow a cover crop early or late in the season.
- Consider companion planting and undersowing to keep beds full
- In general, plants that grow in different spaces / times might make good companion plants. Carrots can grow well along the edge of a tomato bed. Planting corn and pole beans together takes advantage of their complementary growing habits. Sow red clover seed under corn (main crop) in early summer. Once you harvest the corn, the clover will get more light and continue growing (and boosting soil nitrogen) until the following season.
- Mulch around existing plants
- Consider growing Russian comfrey/Bocking 14 as a nutrient-rich mulch. This variety of comfrey is a hardy perennial in our area. Unlike the aggressive re-seeder that grows wild, this one will not spread by seed. Comfrey contains nitrogen, phosphorus, potassium and trace elements that plants need to grow. Cut leaves and place directly on beds around existing plants to mulch, fertilize, increase microbial activity, and add organic matter all at once. Since it grows back fast, you can harvest comfrey leaves at least 3 times per season. Bees love the flowers.
3. Compost everything. Adding compost to the garden increases organic matter, improves drainage and structure, and increases microbial and invertebrate life.
- Try not to let biomass leave. Even weeds can be composted–just leave them to completely decompose before spreading them back into beds.
- Collect clean leaves and pesticide-free grass clippings from neighbors who do not use them. Combine these materials with compostable kitchen waste.
- Woody brush and tree trimmings will take awhile to decompose, but one can bury them to raise low places in the garden. They can also be coarsely chopped and used as mulch, like wood chips.
additional resources:
The Living Soil Handbook: The No-till Grower’s Guide to Ecological Market Gardening by Jesse Frost (Chelsea Green Publishing, 2021). This text was written primarily for professional market gardeners, but the ideas can be applied to small spaces.
Check out the videos and books of Charles Dowding. His approaches are targeted to backyard / small-scale gardeners. https://www.charlesdowding.co.uk