Deciding Whether or not to Divide Lavender
Use cuttings instead of division to create new plants. Try to propagate lavender plants through cuttings instead of division, if your goal is to create more plants. Cuttings have a high survival rate and are easier to start. Division significantly increases the chance of plant death, and should only be used if necessary for the survival of the plant.
If your lavender is overgrown, try pruning instead. Due to the high risk of death following division, even an overgrown lavender plant should usually not be split apart. Prune away about ⅓ of its branches instead, leaving a little of the young, green growth on the plant. Ideally, prune the lavender plant in spring or early summer, just after new growth begins. Pruning in autumn can cause the plant to waste energy on new growth, leaving it vulnerable to frost. Do not prune lavender plants in the first year, when they are establishing roots. If the old, woody growth is already too large for your garden, consider taking several cuttings and removing the old plant entirely once the new ones have been established for a year. Division is a more rapid but riskier solution.
Before considering division, look for a consistent decrease in flowering from year to year. Pay attention to how many flowers your lavender produces, compared to previous years. A slight or temporary decrease may be due to differences in the weather. A safe move may be to start new plants from cuttings, and continue to watch the progress of the old plant.
Examine the center of the lavender plant. Older lavender plants may begin to die in the center, only producing flowers around the outside. This is one of the few situations in which dividing a lavender plant may be necessary. However, any lavender plant has a significant risk of death following division. Opinions are divided on whether a younger or older plant has a lower risk from division.
Taking Cuttings from Lavender (Softwood or Hardwood Methods)
Begin in spring or summer. Take the cuttings during the warm growing season, or roots may fail to form. Cuttings have the best chance to become established if you cut them early in springtime, but if you want additional flowers, you may wait until early or mid summer, then take the cuttings after the plant has bloomed. Waiting later than mid summer is not recommended unless you live in an area with late or no frosts, as the plant needs at least six weeks to grow roots before the ground freezes.
Select a branch with at least two leafy nodes. "Nodes" are the clumps on a branch from which a cluster of leaves sprout. Select a young branch, low on the plant, with at least two nodes. There are two different methods of selecting a branch: Softwood cuttings use only soft, new-growth material from this year, that has not yet become brown and woody. These cuttings will grow fastest, but are only usable if the soft material is at least 5 in. (12 cm) long, and includes at least two leafy nodes. Hardwood cuttings include woody, brown stem material, but must also have at least an inch or two (2.5–5 cm) of soft, new growth at the tip. These require a root stimulator to encourage root growth, available at a gardening store.
Acquire a root stimulator (optional with the softwood method). A root stimulator is necessary for growing hardwood cuttings. It is optional for softwood cuttings, since the young stem will grow roots without it. A root stimulator may be useful for a softwood cutting if you removed it from the mother plant late, less than six weeks before the first expected frost. Check the label and ingredients of a root stimulator before purchasing. Select a root stimulator that contains a root hormone, not just fertilizer and vitamin B1.
Prepare small pots or a starting tray of special soil. Prepare a seed starting tray or small flowerpots to place the cuttings in for the first few weeks after cutting. Because plants without roots are sensitive to both drought and excessive moisture, use a special mix of 50% organic compost and 50% perlite to retain water at the correct level. Similar mixes sold at gardening stores can be used as well, such as a mix of sphagnum moss and perlite. Terra cotta flowerpots are preferable to plastic ones due to their "breathability," especially if you soak the flowerpot in water overnight before continuing to the next step below.
Cut the branch with a sharp, clean knife. Sharpen and clean a knife if necessary, to prepare for a tidy cut with low chance of infection. Slice off the selected branch just below a leafy node, removing a cutting at least 5 in. (13 cm) long, including at least two leafy nodes. The longer the cutting is, and the more nodes it has, the more likely it is to be successful. Using scissors is not recommended, as they may pinch the stem and make it more difficult for roots to emerge.
Cut off all but the top cluster of leaves. Leave the top cluster of leaves alone, as they will provide energy for the new plant. Use your knife to cut all other leaves off the plant, so it directs its energy at root development rather than excessive foliage growth. Be careful not to damage the bark while removing the leaves.
Dip the base of the cutting in a root stimulator (optional with the softwood method). Follow the instructions on the label of the root stimulator to dilute it to the correct strength, if your root stimulator is concentrated or in powdered form. Dip the bottom ¾ inch (2 cm) of the cutting, at the cut end, into the prepared root stimulator solution.
Plant the cuttings in the prepared containers, and water thoroughly. Plant the cuttings in the containers you prepared earlier, just deep enough to keep them steady. Give them a generous quantity of water immediately after planting, relative to the small size of the container.
Keep damp and shaded, but gradually expose to less water and more sun. Overwatering is a common mistake for new lavender cuttings. After the initial soaking, only water the cuttings when the soil begins to dry out, not when the soil is still moist. Shade will help minimize damage from the stress of transplanting for the first several days, but after this the plant can be moved incrementally to brighter environments. Greenhouse environments may be too damp for lavender cuttings. However, if the cutting is looking limp or dry after one or two days, moving it to a greenhouse or under a plastic bag may help it retain moisture until it develops roots.
Transplant into a larger pot or the ground once roots develop. After at least three weeks, and more commonly six weeks or more, strong roots will have developed in the small pot or starting tray. Once the roots have bound the soil together in the container, you can move this soil and the lavender plant into a larger flowerpot or flower bed. Plant in rich, well-draining soil and care for it as you would any lavender plant.
Taking Cuttings from Lavender (Layering Method)
Choose a small, young branch near the base of the lavender. For each cutting you plan to make, select a small branch attached to the outside base of the lavender plant. A young, bendable branch is required, or a branch growing horizontal just above the soil surface. There are several related methods of propagation referred to as "layering." This one is simple and low-risk, but can be labor-intensive if you plan to create more than a few cuttings. Refer to the tips below if you want to turn your lavender plant into dozens of new cuttings instead.
Bury the middle of the branch in a shallow hole. Dig a 4–6 inch (10–15 cm) hole in the soil, a short distance from the mother plant. Position this hole so you can bend the middle of the selected branch down into it, with the leaves and flowers at the end above ground on the other side of the hole.
Anchor the branch in place. Hold the branch in place with rocks or a bent stake to prevent it springing out of the hole. Bury the center of the branch in soil to fill the hole, leaving the flowering end above ground.
Keep the buried branch moist. Water the buried section occasionally, keeping it moist but not soggy. Take care not to let the soil dry out during hot summer months. Watering is not recommended while the plant is dormant for the winter. Mulch can help the soil retain water, but may cause plants to overheat during hot weather.
Dig up and cut the branch after at least three months of growing season. While you can begin this process any time, the branch may not develop a strong stem and roots until the growing season in spring and summer. After three or four months of growth, preferably as cool autumn weather begins, carefully dig around the buried branch to look for roots. If they are present and clumping the soil together, cut off the branch so all the roots are on the same piece as the flowering end.
Transplant the cutting as a new lavender plant. Move the cutting directly to its new location, moving the surrounding soil along with it to avoid damaging the roots. Keep the plant sheltered from wind until stronger roots develop, and care for it as you would any lavender plant.
Dividing a Lavender Plant
Use this method only as a last resort. Lavender plants, unlike many perennials, do not handle division well. Read the section on deciding how to propagate lavender for more advice, or refer to either section on cuttings instead if your main goal is to produce new lavender plants.
Divide in early spring. Lavender plants are dormant during winter, although they may retain their greyish-green color. Wait until early spring to divide the plant, but do not wait until the plant begins the growing season in earnest.
Identify areas for division. If the center of the plant is dead, you should be able to identify individual clusters of stems circling the dead area, attached to the same section of roots. Plan to divide the plant so each new section has at least three to five growing stems and roughly equal shares of the root base. This may require you to include multiple clusters in one division.
Dig holes for the divided plants. As a rough guide, each hole should be about twice as wide as the root ball, and approximately 12 inches (30 cm) deep. Keep in mind that these root balls will be smaller after division.
Add enriched soil to the bottom of the hole. Organic material such as compost or pine bark can be mixed into your garden soil to use as backfill, or the material can be placed in a layer about 3 inches (7.5 cm) deep at the base of each hole. Optionally, add a small amount of fertilizer high in phosphorus and potassium to the base of the hole as well.
Dig the lavender plant partially or fully out of the ground. If the plant is not excessively large, the center is not dead, or separate divisions are not easily visible while the plant it is in the ground, you may wish to remove the entire plant before dividing it. Otherwise, remove portions of the soil around the plant to increase visibility and access to the root ball. Pry down on the handle of the shovel as you move around the plant until the plant releases from the ground.
Use a shovel to cut apart the root ball. Most lavender plants cannot easily be pried apart, but if your variety grows discrete clusters, you may attempt to pry them apart with two garden forks. More commonly, you will need to use a clean, sharp shovel to cut the lavender plant as you decided above, then use garden forks to pry apart the entwined roots.
Plant each section in its own hole. Plant each new lavender plant to the same depth it was planted previously, gently tamping down the soil around it as you fill the hole. Water thoroughly after planting to encourage new roots growth and set the plant in the soil. Continue to care for the lavender as usual.
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