The Purple Flower That Boosts Soil But May Be More Hassle Than It's Worth

From pest control to soil enhancements, avid gardeners are always on the lookout for new ways to use companion planting to benefit their gardens. With the right companion plant, you can prevent damage from wildlife, improve soil nutrients, attract pollinators, deter weeds, promote plant health, and so much more. But sometimes the downsides of a companion plant can outweigh the benefits. Such is the case with the stunningly beautiful purple lupine flowers (Lupinus spp.). 

These hardy perennials grow in USDA zones 3 to 7, and they are recognized for improving soil quality. However, there are certain downsides, such as spreading habits and toxicity, which may leave some gardeners with more work and stress than they're worth. Of course, other gardeners may think these downsides are a small price to pay in comparison to the benefits. It all depends on your personal preference and your region. However, it is best to be fully aware of the pros and cons of planting lupines before adding them to your garden.

Lupines aren't actually flowers; they are technically a type of legume belonging to the pea family. As such, they have the same properties as other legumes in terms of contributions to the soil. Their main benefits include improvements to the structure and fertility of the surrounding soil once they are established. They can improve soil structure because of their deep roots, which are able to break up compact soil to improve drainage conditions. In addition, lupines are known as nitrogen fixers because they enrich the soil with nitrogen, which helps with crop rotation. They have been known to be used as companion plants for vegetables that need additional nitrogen.

Overall, lupines are widely praised for their contributions to soil health. Of course, there are some companion planting mistakes everyone makes that you should make an effort to avoid. Be careful to research both the benefits and the downsides of companion plants like lupine before planting.

It is important you consider everything you should know about lupine flowers before planting them, such as how they grow and their impact on the local environment. The first, and most recognized, downside of planting lupines is that they are aggressive growers in many regions. The status of these plants has led to controversial approaches by national organizations and state wildlife conservation efforts.

Though lupines are not officially listed as invasive anywhere in the U.S., the bigleaf lupine (Lupinus polyphyllus) threatens native species in some eastern and Midwestern states, like Maine and Minnesota. However, the wild lupine, or sundial lupine (Lupinus perennis), is actually native to those regions. If you do choose to plant lupine in your garden, make sure you're planting a species that's appropriate for your region, and you will probably want to remove the seed pods before they drop to prevent unwanted spreading.

The other common issue with lupine that could have a negative impact on gardeners' families and pets and local wildlife is the toxicity of the plants. All parts of the plant are considered toxic for both humans and animals when ingested. Not only does this pose risks to your family if you have small children or pets who may mistake the seed pods for peas, but it also poses risks for local wildlife. If you allow the plant to go to seed and it spreads to nearby pastures, it can impact livestock as well.