Soil drainage is a very important factor to consider when planting Salvia, Agastache, Lavender, Penstemon and other perennials that like "well-drained" soil. The essential element in well-drained soil is oxygen, which is just as important as water in growing healthy plants. Soil that is water-logged does not drain well and is anaerobic (oxygen deficient) resulting in drowned and rotted roots.
In addition to enabling more oxygen to get to plant roots, there is another great benefit to improving drainage: it takes more heat to warm up water than it does to warm up soil, so you can count on an earlier start to your planting season if your soil isn't water-logged.
Identifying Native Soil Types
How you create "well-draining soil" is dependent upon the makeup of the soil currently in your garden.
Sandy soils will drain easily—perhaps too easily. In addition, sandy soils are notoriously bad at holding nutrients, requiring more fertilization. Amending the soil with organic matter will help on both counts.
Clay soils often hold too much moisture, squeezing out the oxygen between soil particles and producing a dense texture that is difficult for roots to penetrate. Compounding that problem, clay soils can crack at the surface when dry, creating fissures which expose roots to sun and arid heat. And as it dries, clay uses reverse osmosis to pull water OUT of the roots of plants in order to maintain its moisture level. Sticky and heavy when wet, hard as a rock when dry—if you have clay soil and wish to preserve your tools and sanity, amendments or raised beds are a must.
Caliche is a combination of calcium carbonate and clay. This combination forms a layer of very poorly draining white chalky alkaline clay. A caliche layer will typically occur from 6 to 12 inches below the surface soil layer. Dealing with it isn't easy—often requiring a pickax and a ferocious battle of wills. When planting deeply rooted trees and shrubs be sure to "punch through" the caliche layer to the soil below. This will greatly facilitate drainage through the hardpan.
Enriching & Improving Native Soils:
To improve the fertility and water holding capacity of sandy soils dig in compost. Compost can also be added to improve air penetration and drainage in clay soil. Include Yum Yum Mix fertilizer, Soil Mender Mineral Boost trace minerals and phosphate at recommended rates and dig the compost into the native soil.
Note: Avoid too much compost; use amendments in a 1/3 compost to 2/3 garden soil ratio. Also, keep in mind that even bagged "topsoil" should be mixed into the existing soil and not used by itself.
Creating "Well Drained" Soil In Clay
The essential element in well-drained soil is oxygen. When planting perennial plants that like well-drained soils in clay, the best thing to do is to create a raised bed or berm (mounded pile of soil). Mix the native clay half and half with coarse sand or crusher fines. (DON'T use fine sand; this will create concrete.)
If planting hardy garden perennials you should add compost and Yum Yum Mix to the soil (1/3 to 2/3 ratio) before mixing the soil with the sand. Mix the sand and enriched soil as you are filling the raised bed or piling the berm.
For plantings that include Penstemon, Salvia and other xeric native plants, mix only sand and clay leaving out the compost. Compost and Yum Yum Mix are mixed by the handful into the individual planting holes to avoid an overly enriched soil mix.
‘Royal Velvet’ English Lavender (Lavandula angustifolia Royal Velvet) is very showy in bloom. It is covered with long stemmed, dark navy blue and lavender flower spikes. The 3 to 4-inch long flower spikes, which are much longer than ‘Hidcote’, hold their dark color superbly as a dried flower.
Thumbelina Leigh is a robust dwarf growing English variety with plump, deep lavender-blue flower spikes, and a strong, sweet fragrance. Maturing to a height of about 15 inches, it is one of the most compact cultivars in cultivation.
FlowerKisser® Arizona Snow Agastache (Agastache urticifolia 'Alba') is a pure white flowered form of mountain hyssop, selected for its exceptional cold hardiness and nectar-rich flowers. Stunning flowers and fragrant foliage make this a must-have addition to attract native bees and butterflies. Its very upright growth habit make it a wonderful choice for the perennial border. Deer and rabbit resistant. A 2020 High Country Gardens Introduction.
Agastache rupestris (Licorice Mint Hyssop) is one of the best, most durable species in the Agastache family. With smoky orange flowers held by lavender calyxes, the entire plant is scented like licorice and mint. A 1996 High Country Gardens introduction. Drought resistant/drought tolerant perennial plant (xeric).
Agastache Glowing Embers is a fantastic selection of Licorice Mint Hyssop (Hummingbird Mint) with fragrant foliage and glowing orange-red tubular flowers that are a favorite with hummingbirds. Plant in containers to enjoy this plant in the eastern U.S. Exclusive. 24-26" tall x 24-28" wide.
Blue Blazes is a large growing hybrid hummingbird mint with lavender-purple flower spikes. Very long blooming, its flowers attract hummingbirds, butterflies, and bees making it an essential perennial for pollinators.