How Seed Dispersal Strategies Affect Harvesting Methods with IRC

Southern California’s native plants have spent thousands of years perfecting the way they release their seeds. At Irvine Ranch Conservancy (IRC), those natural strategies guide nearly every step of the harvesting process, from when staff and volunteers head into the field to how seeds are cleaned, stored and prepared for future restoration.

Seed harvesting at IRC is never a one-size-fits-all operation. It is a dynamic relationship built on observation, timing and respect for the evolutionary traits each plant has developed. IRC’s strategy involves a careful balance between letting nature lead and stepping in at just the right moment to collect what the land is ready to give. 

By aligning harvesting methods with natural dispersal traits (wind, gravity, and animals), IRC ensures that seeds behave as they would in the wild, only with a little human help to guide them toward restoration sites. It also protects genetic diversity, ensures high-quality seed for restoration and maintains the timelines and rhythms that native species depend on.

Wind-Dispersed Seeds

Wind-dispersed species are among the most diverse plants IRC works with. Their seeds are designed for flight, often featuring pappus structures, silky hairs or feathered bristles that help them drift or float in the air to new locations. Native examples include Goldenbush (Isocoma menziesii) and other coastal sage scrub species.

How IRC harvests them:

• Landscape vacuums mimic the pull of the wind, gently drawing seeds into a container, a newer and highly effective technique.
• Bucket shaking works for species whose seeds detach easily with a little movement. This requires close monitoring to catch the moment when seeds loosen but before the wind carries them away.

For wind-dispersal plants, weather-watching becomes essential. One strong wind event can scatter an entire field before staff or volunteers have a chance to harvest the seed. 

Gravity-Dispersed Seeds

Gravity-dispersed plants rely on seeds simply falling to the ground. Some drop seeds gradually as fruits dry, like sagebrush (Artemisia californica) or buckwheat (Eriogonum fasciculatum), while others burst open dramatically, such as lupine (Lupinus albifrons) or poppies (Eschscholzia californica).

How IRC harvests them:

• Landscape fabric mats are placed beneath plants that “pop and drop,” catching seeds before they hit the soil. Seeds are then swept and gathered from the fabric.
• Bucket shaking also works, but timing is everything: too early and the seeds will not release, and too late and they are already on the ground.
• Full-stem harvesting is used when plants reach 50-75% dryness. Stems are collected early enough to prevent loss but late enough to ensure viability. These stems are then run through a thresher to free seeds from pods or fruits.

These species often require multiple checks each week when nearing the right time, because once pods dry, they can drop or explode without warning.

Animal-Dispersed Seeds

Some plants rely on wildlife to move their seeds. Fruiting species attract birds and mammals that eat the fruit and pass the seeds through their scat. Native examples include elderberry (Sambucus mexicana) and toyon (Heteromeles arbutifolia). Other species produce barbed or sticky seeds that cling to fur to travel to new locations, like purple needlegrass (Stipa pulchra) and ambrosias (Ambrosia acanthicarpa).

How IRC harvests them:

• Hand-picking or clipping is required for wet fruits, which can not go through a thresher and must be processed quickly to prevent mold.
• Hand-picking is also the only effective method for hitchhiker seeds.

Because these seeds require such careful handling, this is the most time-consuming harvesting method and often the trickiest for collecting large quantities.

Each dispersal strategy and seed type also influences seed cleaning (air separation, clipping, threshing, hand-sorting), dormancy-breaking techniques (heat, smoke, scarification, gibberellic acid), storage timelines (some seeds remain viable for up to five years) and timing of sowing (December-April when moisture supports germination). 

Late spring into summer is the busiest time for harvesting, especially at the Native Seed Farm. If you are interested in getting involved, Growing Together at the Native Seed Farm volunteer activities take place most Fridays and Saturdays and are open to the public with a simple signup. These sessions often focus on harvesting during peak season. Learn more at letsgooutside.org and join in!