A whiskey barrel isn't elegant, but the sturdy, rustic container works beautifully as a miniature garden space for colorful perennials, as long as the barrel has proper drainage and is filled with a well-draining potting soil. Each barrel, generally about 2 feet in diameter with a height of up to 18 inches, provides ample space for several of your favorite perennials. Combine perennials of various sizes and shapes for extra interest.
Proper drainage is critical for healthy perennials. Without drainage, your carefully planted perennials are likely to rot and die fairly quickly. Whiskey barrels purchased at nurseries or garden supply centers often have pre-drilled drainage holes. If not, you can use a drill to create several 1/2-inch holes in the bottom of the barrel. Cover the holes with a piece of landscape fabric or window screen to keep potting soil from washing through the holes. Perennials perform well in a lightweight, peat-based commercial potting soil, but a generous handful of compost improves drainage and increases fertility. Additionally, a general-purpose, slow-release fertilizer mixed into the potting soil at planting time provides nutrients that get perennials off to a healthy start.
Consider the growing needs of each perennial before planting your whiskey barrel. For example, don't combine sun-loving plants with plants that prefer shade. The thriller, chiller and spiller method is an effective and simple way to design a container planting. The thriller is one tall, dramatic focal point in the middle of the barrel. Surround the thriller with fillers -- low-growing, bushy plants that fill in the space around the filler. Lastly, plant trailing plants or vines around the inside edge of the barrel so the plants drape gracefully over the edge of the barrel. Plant each perennial at the same depth it was planted in the nursery containers because planting too deeply may cause the roots to rot.
Because whiskey barrels hold a large amount of potting soil, the soil doesn't dry as quickly as potting soil in small containers. However, it is important to check the potting soil every day during hot, dry weather. Water the perennials whenever the potting soil feels dry. Avoid overhead watering, which is less effective because water doesn't always reach the roots. Instead, water slowly at the base of the plants with a garden hose or watering wand until water trickles through the drainage hole. Most perennials perform best if the soil is allowed to dry slightly between waterings, as soggy soil sets up ideal conditions for mildew, rot and other diseases.
A 1- to 2-inch layer of mulch such as shredded bark or dry grass clippings helps keep perennial roots moist and cool, and the mulch enriches the potting soil as it decomposes. Perennials require regular feeding to provide the nutrients needed to produce blooms throughout the season. If you add slow-release fertilizer to the potting soil at planting time, wait a couple of months, then feed the plants a dilute mixture of a water-soluble fertilizer every seven to 14 days. Most perennials benefit from regular removal of wilted blooms, which stimulates continued blooming throughout the season.