Lavender is a wonderful herb to have in our Tucson garden. It provides color and makes an excellent groundcover/productive plant in our landscape. Once established this plant does very well in our Zone 9 climate. If you place it in the landscape, the ground does need to be prepared well so that water does not sit and cause this plant to wilt and die. I have specifics on this below. It, like most herbs, needs good drainage. But more importantly, the soil around it should be loose so that the roots can grow outwards. This plant survived our Tucson winter and today looks wonderful. Lavender provides a wonderful smell in the air PLUS the leaf structure, similiar to that of the Rosemary, has a nice silver grey tone to it that will add contrast against other green plants in your garden. In fact, if you've been reading this garden journal since the beginning, you may recognize that plants with silver grey foliage seem to do very well in our desert climate and there are reasons for that:) But more on that later in another post......Here is some information on how to prep your soil for lavender. I think this is the most important thing to know when dealing with herbs. If you get the soil right, they will thrive. Don't overwater and don't let these plants sit in water and you'll be amazed by their performance......
"Most lavenders are started from cuttings taken from Mother plants. This is both fast and accurate, producing an exact replica of the original plant. Starting Lavender from seeds sounds like a great inexpensive way to get all the lavender you desire but it can have some major drawbacks. The first obstacle is finding the seeds. Even though Spanish, Yellow, and other species Lavenders can be started from seeds, it is usually only the Lavandula angustifolias--Hidcote, Vera, and Munstead-- that are available as seeds. The second drawback is what we call 'low and slow' germination. Lavender seeds have a short shelf life, and therefore the germination rate (how many seeds out of 100 come up) is usually pretty low. They can also take a long time to sprout (two weeks or more) and this invites fungus to the seed tray, often causing the seed to rot before it can sprout. Seeds benefit from light, so cover lightly when sowing. The germination temperature should be around 70 degrees and spring seeding is more successful than fall seeding. Those seeds that do sprout will take one to three months before they have enough roots and top growth to allow successful transplanting. Adding fertilizer to the sterile medium used in the seed tray can help the little plants get off to a better start, but it can also invite fungus in cool, humid situations. The third disadvantage is the time it takes for the seedlings to get to a good size. After they are transplanted into small pots, the plants will be about three inches tall and have a single stem. It will take another three months or more to make a plant substantial enough to transplant to a larger pot or to the garden. The fourth inconvenience is the difference factor. Because little care has been taken over the years to insure that the seeds have not crossed with each other, the plants will be varying shades of color. They might also vary some in height and width. The perfect hedge of Hidcote Lavender she had dreamed about and worked so hard to grow the plants for turned out to be more like a cottage garden: still beautiful, but irregular in form and color. And, lastly, the most popular Lavenders (the Lavandula x intermedias; sometimes called Lavandins), either do not make seeds or the seeds are sterile, so you will never see a seed packet of these.
The most important factor to get right with Lavender is drainage. Soggy areas should definitely be avoided. Incorporate organic matter if necessary to make a loose friable soil. Compost is the best amendment because it is fertile and has uneven particle sizes. Uneven particles in the soil create better air spaces and give the roots better anchors to attach themselves to. Check the soil's pH (potential hydrogen) to make sure it falls somewhere between 6.5 and 7.5. If the soil is too acidic the Lavender will not thrive. If the soil is too alkaline, the nutrients are 'tied' up in the soil and the plant cannot use them. Yellowed growth can be indicative of a soil that is out of balance. Adding compost can help to balance the pH.
If you are going to plant a hedge or a massive amount of Lavender, make sure the ground is cleared of weeds. Solarization works to remove not only tenacious weeds, but also kills weed seeds. Small Lavender plants cannot compete with aggressive weeds, and weeding after they are planted can be a huge hassle. Weeding often becomes such a chore that Lavenders are overrun and eventually die in a neglected field.
Mulching with a small particle mulch or compost after planting helps with the weed control, but avoid mulching right up to the stem of the small plant. Instead, leave a collar about two inches wide around the plant.
If you are in hot, humid areas, try planting Lavenders in a raised bed or on a mound. Leave plenty of room between plants for air circulation. Lavenders are not ideally suited to heat and humidity, so be prepared for problems, such as fungal disease and rot.
For ultimate show, space plants according to their height measurement. For example, a Grappenhall Lavender is listed at 3 to 4 feet. By spacing these 3 or 4 feet apart, the effect when the plant is blooming is spectacular. If it is more important that the plant make a tight row or hedge, then plant closer together.
If planting in pots, make sure to repot every spring into a larger container with fresh soil to allow the plant to continue to mature and to provide as many flowers as possible. A good, coarse, sterile potting soil with organic fertilizer mixed in works best.
In the ground or in a pot, full sun is a must. If the garden is crowded, plant near a south-facing wall. Even the Lavender at the north end of the row will be shorter and bloom later. In hot areas, some late afternoon shade can be tolerated without sacrificing the glorious mounded shape and rising pincushion effect of the flower wands.
Lavender in the field rarely needs fertilizer, especially if compost is applied as a mulch. More often, problems arise because the soil is not healthy. Avoid chemicals in pesticides, herbicides, and fertilizers that kill or starve the beneficial organisms in the soil.
In arid regions with no summer water, irrigation will be necessary for the survival of the plants. While Lavender is extremely drought resistant once established, it grows larger and produces more blooms with regular watering. This means that when it is dry, water it. While this may sound obvious, it is important to let it dry out a bit before soaking it again. In humid areas, this can be difficult and the excess moisture often causes death. " End of article. Source: http://www.mountainvalleygrowers.com/lavendercareandtips.htm