Summer Structures
Denver summers get HOT. By late June it is very difficult for plants to adapt in the sweltering heat, so we pause on planting until the return of cooler fall days. As in many dry ecologies, night-time temperatures still drop enough to take advantage of the cool morning temperatures to structure and edit our gardens.
Sculpting with Stone
Denver was built on an ancient clay-based lakebed, which offers challenges of compacted soils through which plant roots have a hard time growing. Water does not absorb well into clay, so typically will pool up or run off. Aeration attempts to address this by poking holes in the surface of lawn areas to loosen the compacted soil and get water to the roots of grassy lawns. However, if we look at cross-sections of lawn soil, we see that grassroots form a shallow mat of biomass that doesn’t do much to break through or amend the clay, so grass lawns end up needing extra water and chemical intense fertilizers on top of the maintenance required to keep them trim. We do not need to look far for alternatives. One of the gifts of clay is that it has a high mineral content, which plants love. With a little attention, we can adjust the structure of the soil to help our plants thrive by opening access for water to penetrate the ground, allowing plant roots to reach depths of soil that don’t dry out as quickly as the top layers of exposed earth.
We live at the base of the Rocky Mountains, so native plants have adapted to grow best in rocky environments. Stones, both large and small, are an effective way to amend soil structure. Squeege is a cost-effective material most often used in construction. It is a mixture of small stones ranging in size from pea gravel to coarse sand, and it is ideal for mixing into native soils to create a matrix structure that is a perfect medium for roots to reach depths they are inclined to grow, while allowing water to penetrate the dense clay. A general ratio recommended by the Denver Botanic Gardens is to mix squeegee into existing soil at 50/50 proportions (half squeege and half soil.) If I am building up garden beds, I will mix the two materials in this quantity to fill in the newly established growing areas. For established beds, squeege may be used as a top dressing called rock-mulch. It will slowly sink its way into the soil and settle into the matrix that allows space for roots to grow deep. A top dressing more than 4” deep will also suppress weeds. In thinking of local ecologies, rock-mulch is best used in sunny areas of the garden to replicate the exposed rocky areas of steppe regions. In more forested areas, I stick with the more traditional wood mulch to serve a similar purpose. The wood chips slowly break down to loosen soils, replicating forest environments. Sourcing bulk materials cuts down on plastic waste while saving money. Ewing landscape supply has several branches around the metropolitan area. My favorite is on South Santa Fe in Littleton as their yard is chock-full of material options. Even small cars can weigh in, load bulk materials in bucket-scale proportions that can easily fit into the trunk of a sedan, then weigh out and save a lot of money.
Large stones may be used to help water flow deeper into the ground, and to maintain moisture in the soil. Crevice gardens are a wonderful way to structure larger stones to replicate our local, rocky ecologies. Kenton Seth is a western slope landscape designer who creates crevice gardens as well as guides on how to build your own: http://www.paintbrushgardens.com/ Stones set vertically in garden channel water deep into the ground to nourish deeply-rooted native plants. While crevice gardens typically structure tight planting slots, there is room to play around with the scale of planting areas. Over the past year, we have been installing new gardens around the Stiles African American Heritage Center. We installed thick pieces of flagstone vertically to create raised beds into which we have cultivated an assortment of (mostly) native plants. We decided to build larger scale crevices as the garden beds to encourage plants to grow bigger, while keeping their roots contained. This way, the stones keep more aggressive plants from taking over while letting them grow to their full size. Stones laid horizontally keeps moisture from evaporating, so plants around the perimeter may grow their roots under the rocks and stay moist even during the hot dry spells that define our summers.
A Succession of SEEDS
Starting with spring ephemerals, plants go to seed throughout the summer and fall. Allowing some plants to re-seed is a wonderful way to fill in garden spaces so that plants grow ‘petal to petal’ in an effective way of reducing weeds and the need for mulch. Whether we use rock or wood mulch, we should be aware that they are extracted from elsewhere and take an environmental toll both in the production and transportation of the material. Exposed soil invites weeds, so a garden full of mature plants doesn’t have as much space to let them take hold. Furthermore, pollinators benefit from banks of flowers more than singular plantings. They are more efficient at pollinating the same kind of flower en-masse, instead of having to re-learn how to access pollen in different kinds of flower structures.
We can also gather seeds to save, to share or to establish in new areas of our gardens. Plants that are established from seed on-site are heartier and more adapted to their location from the start. Seeds are ripe when they scatter easily. We like to be messy when we collect seeds so that many fall to the earth around the mother plant to replenish the plant-stock and fill in open ground. We are also mindful to leave some for the seed eating birds who pass through our gardens! These protein rich nuggets are an essential part of many birds’ diets, especially when they start fall migrations. Seeds typically do not like to be stored in plastic. To save them to sow at a later time, either store them in glass jars, or place them in small paper envelopes, which can then be stored in plastic zip-lock bags to help preserve their moisture. Store in a cool, dry place to sow in late fall and winter.
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