Tips for gardeners who are planting annuals
Annuals bring bursts of color, fragrance and life to our gardens and landscaping. At times dismissed for their short life, many are surprised to discover that annuals provide more color in the landscape more quickly and for longer periods of time than any other garden plants.
There are three main types of annuals based on their cold tolerance and ability to withstand frost.
Hardy annuals are resilient plants sown directly outdoors that can withstand colder temperatures and even light frost. Examples include pansy (Viola x wittrockiana), calendula (Calendula officinalis) and sweet pea (Lathyrus odoratus).
Half-hardy annuals are plants that can tolerate some cool weather but are more sensitive to frost. They benefit from starting seed indoors and then transplanting. Marigolds (Tagetes spp.), petunias (Petunia x hybrida) and cosmos (Cosmos spp.) are common half-hardy annuals.
Tender annuals are delicate plants that are frost-sensitive and cannot survive cold temperatures. They thrive in warm climates and should be planted after the last frost date, typically May 14 for Butler County. Zinnias (Zinnia spp.), impatiens (Impatiens hawkerii, Inpatiens walleriana) and begonias (Begonia spp.) are examples of tender annuals.
When selecting your annuals, look for insect-, disease- and deer-resistant species. Selecting and installing healthy plants in your garden can reduce, or possibly eliminate, the usage of pesticides and can also reduce maintenance.
When selecting your planting site, consider that most annuals need full sun (at least four to six hours a day); however, there are shade-tolerant annuals available for locations with less sun. Avoid planting in areas of poor drainage which could lead to root disease and growth issues.
Once you select your site, it is best to prepare your soil for optimal growth and blooms. Perform a soil test if the site is new or you have not tested in the previous three years. Most annuals prefer a soil pH of 6.0 to 6.5. For clay soils, mix in at least 2 inches of pine bark humus, compost, leaf mold or small pea gravel to improve drainage and aeration. For sandy soils, mix in 2 to 3 inches of pine bark humus, composted leaf mold or peat moss to improve water retention.
Before planting, be sure to water your annuals prior to removing them from cell packs or pots. The ideal planting time for hardy annuals is at least six weeks before expected before the first fall frost date, approximately Oct. 8 in Butler County, to allow time for root development.
Plant annual transplants after the last chance of frost, usually the end of May in Butler County, and your soil has warmed. Select annuals that are season-appropriate to achieve the best results. For example, heat-loving annuals may struggle if planted too early in spring, such as impatiens cultivars like SunPatiens (Impatiens x hybrida SunPatiens) or ageratum (Ageratum houstonianum). Garden centers typically offer appropriate annuals for the current or upcoming seasons.
Before planting, arrange the plants while they’re still in their pots. Dig a shallow hole large enough to cradle the root ball. For multiple annuals, create a hole with a trowel and drop the plant in. For in-ground beds, consider mature plant size for proper spacing. Plant at the same level or slightly lower than they were in the container. When the area is prepared, gently remove plants from containers by squeezing the pot or flipping it over. Avoid pulling the plant by its stems, which can break the stem and kill the plant.
Firm the soil around your plant to eliminate air pockets, and then water thoroughly. The first few weeks are when the plants develop their root systems, so pay close attention to keeping them well-hydrated. Watering thoroughly and deeply will help to promote deep root growth. Allow the soil surface time to dry before watering again. For best results, water early in the morning to allow the plants to dry quickly and avoid overhead watering as it can spread leaf diseases, such as downy mildew and damping off, and root rot.
For optimal growth, apply a complete fertilizer (10-10-10), a complete slow-release fertilizer or complete organic fertilizer, following the directions on the label. For additional growth, repeat the fertilizer application at six-week intervals. To encourage continued flowering through the season, remove flowers as they fade and before seeds are formed.
Heavy pruning can also invigorate some annuals, such as petunias (Petunia spp.), geraniums (Pelagonium x hortorum) and zinnias (Zinnias spp.).
Keep your garden clean and weed-free and be alert for early signs of insect damage to reduce the need for pesticides. To reduce the impact on pollinating insects, any pesticides should be applied late in the evening, and be sure to always read the label carefully before use.
While annuals may be fleeting, their impact can be lasting. Whether you’re planting marigolds, petunias or zinnias, embrace the joy of gardening and watch your landscape bloom!
Learn more about annuals at Penn State Extension extension.psu.edu/how-hardy-are-your-annuals# or extension.psu.edu/old-fashioned-annuals-for-the-home-landscape.
If you have questions about planting annuals, call the Penn State Extension Master Gardeners of Butler County at their Garden Hotline at 724-287-4761, ext. 7, or email the Master Gardeners at butlermg@psu.edu.
Julie LePere is a Penn State Extension Master Gardener of Butler County.
