A “spiller” is a plant that just tumbles out of the pot. These are awesome as hanging plants, and an eye-catching way to decorate your potted arrangements, by playing the role of understory plant and soil cover. It's a decoration for your pot, as well.

The main role of a spiller is to sprawl over the side of the container and tumble toward the ground.  Any plant that spills over or weeps over the side of the pot will do, if it's short enough and doesn't overtake your container. There are some lovely conifers that can do that, too. Groundcover plants are naturals for filling all the space at the bottom of your container arrangement, but some don't sprawl or get tall enough to spill. They still look beautiful, and i use them. Most perennial spillers and groundcovers cover both features. Covering the soil at the base, and adding a draping look at the top of the pot.

A good way to figure out what to plant as a spiller is to use what is generally used in hanging baskets as filler. What flows from those, will flow beautifully at the base of your plants. There are also many herbs that creep that can be used for this purpose, and you get to pinch off fresh herbs for cooking. Creeping Thyme and Trailing Rosemary are great plants for both the looks, and for snipping herbs.

Snow-In-Summmer (Cerastium)

Height: 6 inches tall by 1-2 ft. 
Bloom Color: White, spring and summer.
Full sun
Zones: 3-10

When it blooms, it's almost entirely covered with bright white flowers.It grows fast. It's great for a xeriscaped garden because it has tolerance to drought.  Snow-In-Summer prefers full sun. I find that it does well in sun unless temperatures are above 90. I separate young and healthy clumps from a plant, and pop it wherever i can in the garden. They look great right from the first season.

Sweet alyssum grows in a mounding form to about 12 inches tall and wide. 

It can be planted in your garden or used in a container, where its spreading habit spills nicely. Clusters of tiny white, pink, or purple flowers bloom continuously.

 Butterflies and bees are attracted to the carpet of flowers that smell like honey.

Perfect trailing plant for all themes. I pull some out and grow them indoors in hanging pots for winter. They make great houseplants. Then they go back out in spring to fill my pots and raised beds.

Hardy to zone 3 (- 40°F)

Blooms April - May

One of the earliest flowers to bloom in compact, rounded shapes.

Mature Height: 6”.  Creeps to 20”- 30”.

Grow in full sun to partial shade. 

Zones 4-8

Non-invasive perennial type, and always beautiful as pot spillers, in windowboxes, as climbing or creeping vines, and tumbling from walls. Some hardy varieties stay green through the winter.

Delicate stems. Very hardy, and keeps weeds out. Beautiful at the base of containers and in window boxes. It's hard- to- find foliage in its bright yellow- green color that sets off the boring greens in the garden. 

Can be lightly stepped on, if used as groundcover. Perennial.

No maintenance to speak of, except to divide into more plants, if you wish.

Sweet Woodruff is a mat-forming perennial, most often used as a ground cover or tumbling from windowboxes and pots. 

Plants typically grow 8-12" tall and feature fragrant dark green leaves. Plants will creep non-aggressively, about 1ftx1ft wide per year. 

Division is easy. And you will have more plants for other pots and garden areas that return year-after-year

Blue Star Creeper grows into a thick, fast-growing, low mat, choking out most weeds. Very sweet little plant that covers thickly and spreads.

Deep green with blue star-shaped little flowers. Also comes in white. It grows up to about 6 inches tall. Pretty when used in tops of containers and as a groundcover. Not tall, but it can drape and spread in a gorgeous mat of little flowers draping over pots. 

Though the plant seldom grows over 8 inches tall, it can trail and drape 1-2 feet with the plant spreading out over 12-18 inches.

Trailing Rosemary a low-growing, trailing form of Rosemary. Like other varieties of Rosemary, it has dark green pointy leaves that are rich in aromatic oils.

Small, pale blue to white flowers appear along its branches from March to May. It looks beautiful draping over a rock wall or cascading from hanging baskets and pots.

Long-blooming and drought-tolerant. Especially suited to large container plantings.

They  will trail over the edges of baskets and containers up to 4 feet by the end of the season.  They are great in large container arrangments, hanging baskets, large raised beds and neighborhood plant islands, where they function as both fillers and spillers.

Aubrieta (Rock Cress)

Zones:4-8
Comes In Several Colors
Aubrietta blooms late spring to summer. 

This creeping plant is great as a pot spiller, in a rock garden, flowing over a rock wall, filling in between stone pavers, and as a groundcover in the garden.  Drought tolerant. Deer resistant. Fuzzy green, Mat forming foliage.

Burro's Tail

Annual
A beautiful houseplant in winter.

Draping succulent plant.

Perfect for container arrangements that include agave, yucca, and other tall and bold succulents you would choose as a focus or filler plant.