The Science of Sowing: Designing Custom Seed Mixes for Colorado Landscapes

Scattering a few ounces of seed onto dry Colorado soil can feel more like hoping than planting. Folks who’ve tried store-bought wildflower mixes might know the frustration: despite following instructions, results are often inconsistent. Mixes may bloom for a season or two but can be patchy, lack coherent design, are soon overrun by weeds, or collapse into stands dominated by one or two aggressive species.

Still, direct seeding remains one of the most appealing ways to transform non-functional turf, medians and other tough spaces. Seeds are inexpensive, species are easy to source compared to potted plants, and installation is simple. Our horticulture research team at the Gardens has been investigating ways to make direct seeding more reliable, creating mixes that are beautiful, resilient and long-lasting.

Setting Parameters

One challenge with many commercial mixes is the lack of crucial details. Sowing rates are often given in pounds per acre, which is nearly impossible to scale to a backyard or small urban lot. Even worse, weight is misleading: a gram of lupine seed equals about 30 seeds, while a gram of Artemisia can be nearly 10,000. To improve accuracy, we calculate sowing rates based on the number of seeds per unit area (i.e., 300 seeds per square foot). This method allows us to balance species more precisely and adjust mixes to specific sites.

Another problem is growth form diversity. Most mixes emphasize only wildflowers, overlooking grasses and shrubs—two of the most resilient growth forms in Colorado ecosystems. However, the right ratio of these various growth forms is crucial. Too many aggressive grasses or shrubs, and diversity disappears. But when balanced, each growth form contributes to a stable and enduring plant community.

Choosing the Right Species

Species selection is just as critical. Every plant has unique traits: germination timing, bloom period, lifespan, stress tolerance and competitiveness – among many others. Many mixes rely heavily on species that sprout quickly, which may look good at first but fail to sustain long-term diversity or season-long blooms.

Our approach uses trait-based design. We include fast-germinating species that suppress weeds in the first year while leaving room for longer-lived species to establish. We also screen new species for how they perform over multiple seasons, tracking which ones persist, coexist well with others, and extend bloom time from spring through fall.

Timing Matters

We’ve also studied how sowing season affects establishment. Standard advice is to sow in autumn so cold weather can break seed dormancy. But our trials show that spring sowing—using seeds pre-treated with cold in refrigeration—often yields higher germination, especially when paired with supplemental irrigation in the first year. Losses from winter die-off, predation, and moisture stress may explain why fall seeding performs less reliably.

Built to Last

Direct seeding may never be as predictable as planting nursery-grown perennials. But with thoughtful design, it can be just as successful. By refining sowing rates, balancing growth forms, carefully selecting species, and timing sowing strategically, we’re creating custom mixes that are diverse, resilient and built to last in Colorado’s challenging conditions.