Learn to spot the keepers

One of the first steps toward filling the garden with volunteer plants is learning to recognize young seedlings and not weeding out potentially desirable plants. I remember once failing to recognize the beautiful annual snow on the mountain (Euphorbia marginata) and removing almost all of it from my beds before thinking to leave a few plants to see what they were. Of course, if hundreds of unknown seedlings suddenly appear, it is probably better just to save a small patch than to be overwhelmed by a truly undesirable weed later on.

It’s out of print, but Park’s Success with Seeds by Ann Reilly is a useful reference when trying to discern valuable seedlings from ill-favored ones. As helpful as reference books can be, however, I’ve found that the knowledge gained through experience and patience can be more beneficial. Knowing the history of the garden and what has been planted in the past will help you identify volunteers. Patience and observation are needed as you wait for an unknown plant to become large enough to recognize. Over time, your efforts will be rewarded as you recognize more and more types of seedlings.

Encourage unusual forms

As many gardeners know, variability is one of the features of open-pollinated seedlings, which means the resulting plants can look different than their parents. This variability can lead to disappointment when a double-flower petal trait is lost or an unusual color reverts to that of its plainer parent. But just as often, variability can lead to pleasant surprises. In fact, many cultivated varie­ties originated as spontaneous accidents.

To increase the possibility of positive results, allow only the plants with desirable features to go to seed, removing the seed heads from all other varieties. While plants will still be variable, this type of selection will, when done over time, boost the population of plants with preferred characteristics. For instance, I have a white balloon flower (Platycodon grandi­florus f. albus) that produced a seedling with beautiful snowy flowers streaked with dark purple. Although I had intended to collect seed from this plant, I forgot to mark it and was unable to distinguish it from its more pedestrian neighbors. For this reason, I recommend marking plants with appealing features using a stake or string to keep track of the seeds you want to cultivate.

Manage prolific sowers

Controlling plants that self-seed can be much easier than controlling plants that spread vegetatively underground. Digging up plants that spread aggressively by rhizomes can be difficult; they tend to poke up in the middle of other plants and resist efforts to remove the entire rhizome. To control plants that spread by seed, however, you only need to weed or thin out young seedlings and remove the flowers before any seeds ripen.

When I first planted the delicate orange Atlas poppy (Papaver atlanticum), I made sure every pod ripened, then I hand-spread the seed around the garden. I quickly learned the next season that the plant spreads abundantly on its own, so now I remove all but a few seedpods each year.

Plants sometimes seed so quickly and profusely that they become troublesome and should be removed altogether. As always, before intro­ducing any plant into the garden, check to see if the plant is invasive in wild areas of your region. Cooperative extension services or botanical gardens in some states offer lists of regionally invasive plants.

Growing self-sowers is always a gamble: Seed variability can lead to a disagreeable color, or a species will grow abundantly one year but not the next. Yet the rewards outweigh the disappointments. Self-sowers are economical and breathe new life into designs. Once you can identify and cultivate worthy seedlings, you’ll discover an amazing array of garden treasures.