A high-altitude garden is generally one that is at 7,500 feet elevation and will be in USDA growing zones 3 or 4. It can be challenging for you to have a bountiful garden when the growing season is short, the humidity low and water is scarce. There are easy, simple solutions you can implement to grow a variety of herbs at higher elevations successfully. Begin by starting your herb seeds indoors six to eight weeks before the last frost in your area so you will be able to transplant your herb seedlings as soon as warm weather arrives.
Select a spot for your herb garden that is protected from the harsh, high-altitude winds, yet will receive four to six hours of sunlight a day. A good location that meets those requirements is often close to your house, garage or other outbuildings. The structures will give your herbs wind protection, and ground areas close to buildings usually stay warmer at night, should an unexpected cold front move through.
Spread a layer 3 or 4 inches deep of organic material over the area you plan to grow your herbs.
Use a shovel to work the organic material into the soil, to a depth of 10 to 12 inches. Soil at higher altitudes is usually very sandy and rocky, with little nutritional value for your plants, and a high pH, or alkaline, level. By supplementing your herb garden soil with organic matter, you are adding the nutrients your herbs need, lowering the pH and helping your soil retain water longer.
Use a drip irrigation system or soaker hose to water your herbs and conserve water. Because of the low humidity level at high altitudes, water evaporation happens rapidly. Using a low-to-the-ground watering system allows more water to seep into the soil rather than evaporate into the air. You will need to monitor when your herbs need to be watered by checking the moisture level of the first inch or two of soil for dryness. Water in the morning or early evening to maximize water absorption.
Add approximately 2 inches of mulch around your herb plants to help keep weeds down and help retain moisture in the soil longer. If you use organic matter for your mulch, such as dried leaves or pine needle straw, you will also be supplementing the soil with nutrients and, because pine needles or organic matter are high in acidic content, you will lower the pH in the soil. Your herbs generally prefer a lower pH soil and continual additions of acidic matter will help maintain a lower pH.