Cross-pollination itself generally does not negatively affect the viability of lavender seeds in terms of whether they will germinate or not. In fact, for many plants (including lavender, which relies on insect pollinators), cross-pollination is essential for viable seed production at all.
Here's a breakdown of how cross-pollination relates to lavender seed viability and what it primarily impacts:
1. Viability for Germination (Generally Not Affected Negatively):
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Pollination is Key: For a flower to produce a seed, it needs to be pollinated. Whether that pollen comes from the same plant (self-pollination, if the plant is capable and willing) or another plant (cross-pollination) is generally irrelevant to whether the resulting seed is viable (i.e., capable of germinating and growing). In the case of lavender, many species are not good self-pollinators and rely heavily on cross-pollination by insects like bees to produce a good quantity of viable seeds.
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Increased Seed Production: Studies have shown that access to pollinators and thus cross-pollination can actually increase both the seed production rates and seed viability (the percentage of seeds that successfully germinate) in lavender. More pollination often means more and better-formed seeds.
2. What Cross-Pollination Does Affect: "True to Type" Growth This is the critical point for gardeners:
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Genetic Purity: Cross-pollination does affect the genetic purity of the seeds. If a lavender plant is cross-pollinated by a different lavender variety or species, the resulting seeds will be a genetic mix of both parent plants.
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Variability in Offspring: When you plant these cross-pollinated seeds, the resulting seedlings will not be identical to the plant you collected the seeds from. They will be hybrids, and their characteristics (flower color, plant size, bloom time, scent profile, cold hardiness, etc.) can be highly variable and unpredictable. They may or may not resemble either parent strongly.
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Why Cuttings are Preferred for Specific Varieties: This is precisely why commercial growers and most home gardeners propagate specific, named lavender varieties (cultivars) using cuttings. Cuttings are clones; they are genetically identical to the parent plant, ensuring the offspring are "true to type." If you want 'Munstead' lavender, you buy a plant grown from a 'Munstead' cutting, not from 'Munstead' seed collected from a garden where it might have cross-pollinated with 'Hidcote' or a Lavandin.
Exceptions/Nuances:
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Sterile Hybrids: While rare in common garden lavenders, some inter-species crosses in the plant world can occasionally result in seeds that are viable but produce sterile offspring (like a mule, which is a hybrid of a horse and a donkey and is usually sterile). However, this is not a widespread issue for the typical cross-pollination observed between different lavender varieties or even species like L. angustifolia and L. latifolia (which produce the fertile Lavandin hybrids).
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"Hybrid Vigor": Sometimes, cross-pollination between different, strong genetic lines can lead to "hybrid vigor," where the offspring are even more robust and vigorous than either parent. This is often seen in intentionally bred F1 hybrids. While the seeds from a cross-pollinated lavender will be variable, some of the resulting plants might turn out to be very healthy and desirable.
In summary, don't worry that cross-pollination will make your lavender seeds "non-viable." They should still germinate. However, if you're collecting seeds from your garden and multiple lavender varieties are present, be prepared for genetic surprises and variability in the plants that grow from those seeds. If you need consistent results, always rely on plants propagated from cuttings.
Lavender Farm in Door County Wisconsin. You can buy lavender products online at islandlavender.com