How to propagate  herbs and other perennial plants

One of the coolest things about growing perennial plants, like herbs and flowers, is that it’s really easy to make more of them! Here’s how to propagate perennial herbs to make your garden bigger or increase your harvest. While I’m using herbs (because herbs are my thing) in this post, these propagation methods apply to all perennials.

Propagating perennials

There are three ways to make new plants. Some of the methods work better for some plants than others. Collecting seeds and planting them is also a way to make more plants, but I’m focusing solely on propagation for this post.

Many herbs are perennials and that means they come back year after year. Perennial plants are simply herbs or flowers that typically die back in the fall, going dormant over the winter.

In the spring, perennials make new growth as the weather  warms up. By summer, the plant is the same size, or larger, and covered with new growth.

It’s very easy to grow completely new plants from cuttings or divisions of perennials you (or friends or family members) are already growing.

Annuals

Some herbs, like basil, are annual in many places, meaning they live only one growing season. But because they can grow so vigorously, these non-perennial herbs can be very easy to propagate during their one season. Therefore, I’ve included them in this guide.

For further information on basil, check out Making More Basil.

Keep in mind that most perennial plants want to spread and replicate themselves. Some even NEED to be divided every so often to maintain vigor. Knowing this, it’s better to start with just a few plants and a plan to turn them into more. You’ll save money and you won’t run out of garden space as quickly.

HOW TO PROPAGATE PERENNIAL HERBS WITH CUTTINGS:

Many plants will happily grow roots from a single cut stem or stalk. Generally referred to as ‘taking a cutting’, this is one of the easiest ways to create new plants.

For best results, take cuttings from established perennials that have at least one full growing season under their belts.

Once the plant has started to grow in the spring, it’s ready to donate a cutting. Clip off a small section, at least 3-5 inches tall. This is best done just above where two stems fork.

Seasonal Timing

Both spring and fall are great times to take cuttings to propagate perennials. Early in the year, it’s best to take the cuttings from new growth on the plant. Later in the season, you can take cuttings from new or old growth. Old growth is typically woodier and usually takes longer to produce roots but can ultimately make a stronger new plant.

After you’ve taken the cutting, remove most of the foliage along the stem. This allows the plant to focus energy on making roots instead of supporting leaves. Leave at least two pair of leaves, however, as the plant needs to be able to photosynthesize.

How to propagate cuttings in soil

Put the cutting  into a container filled with moist soil. The buried stem will develop new roots over time. Keep the soil moist and keep the container out of direct sunlight. Cuttings are vulnerable, especially in the first week or two. Too much sun or extreme temperatures will kill them before their roots can establish.

The advantage to rooting cuttings in a container is that it’s easy to move the container to keep the fragile cutting out of harsh weather or searing sun. You can also optimize the soil to make root development easier for the cutting.

Make sure the soil is tightly packed around the cutting. If the cutting isn’t in contact with the soil, it won’t form vigorous roots.

Soil for Propagation

I make my own propagation soil mix by using 1 part coconut coir (an awesome product that’s more environmentally friendly than peat moss) and 1 part horticultural vermiculite, plus a scoop of my worm compost.  Coconut coir holds moisture well, which is very important for developing roots. The vermiculite ensures air can circulate and that water can pass through easily. While it’s important for the soil to stay moist, it’s equally important water can’t build up.  Standing water can rot the cutting. The worm compost also helps retain moisture and provides nutrients to the growing plant.

This is the same soil I use for seed starting, by the way.

Why make your own garden soil?

Doing so allows you to control every component and customize the soil to your needs. Mix more coir in if you’re concerned about plants drying out. Use more vermiculite if drainage is important.

And in larger quantities, buying the components and making your own soil is usually cheaper than bags from the garden center.

basil cutting in waterBasil cuttings with long new roots

Propagating plants in water

It’s also possible to root cuttings in water. Take the cutting as described above and simply plunk it into a glass of water. Keep the water fresh and abundant and the cutting will eventually develop roots.

Is it better to root cuttings in water or soil?

It depends on the plant, honestly. Some people feel that plants develop better roots and are generally stronger if they are rooted in soil instead of water.

In my experience, basil and oregano both love to make new roots in water and do so quickly. Thyme and rosemary, which have thicker, woodier stems, seem more resistant to rooting in water, but it is possible.

The benefit to rooting in water is that you can tell if the plant is making new roots. It’s also very easy to simply stick a cutting in a glass and wait.

A benefit to rooting cuttings into soil is that transplanting the new plant is less stressful. The roots won’t be as disturbed because you can scoop out the soil and put it straight into the hole you’ve dug.

Knowing when the new plant is ready

Whether you use water or soil, wait to see new growth develop on the plant before moving it to the garden. New growth is a sure sign the plant has formed roots and that the roots are working to take up nutrients. Think of new growth as a literal green light to transplant!

Note that many people use rooting hormone when putting cuttings into soil. This is an inexpensive powder that can help roots form more quickly. It’s helpful but not at all essential. Try it and see if you like it, but if you don’t have any, go right ahead and root your cuttings without it.

If you put cuttings in soil:

Keep in mind that the rate of new root development will vary from plant to plant. Woodier plants, like thyme, rosemary or lavender typically take longer to start making roots. By contrast, plants like oregano and chamomile both form new roots very quickly. The best course of action is to take several cuttings and carefully monitor their development.

HOW TO PROPAGATE PERENNIAL HERBS BY ROOTING EXISTING PLANTS:

This technique, called layering, is very similar to taking cuttings, but with a key difference. The section of plant you are rooting isn’t off of the original plant. Instead, you take a small branch or section of the parent plant, bend it gently over to the soil and then cover it with more soil.

Remove any growth from the section you’re burying so it doesn’t rot. Leave the growth on the end of the section intact.

The parent plant continues to provide nourishment for the section, but the soil around it encourages it to make roots. Once the section starts to make new growth and resists being (gently) tugged,  assume it’s made roots. At that point, cut the section off just before the buried portion, carefully dig the section up and admire your new plant!

Seasonal timing

What’s great about layering is that the parent plant does most of the work in nourishing the section. That means you can do this at any point in the growing season. The buried section doesn’t need special care or extra watering. If you aren’t ready to remove and transplant the new plant, you can even leave it on the parent plant over the winter.

Layering to propagate perennials

The drawback is that you have to work with a section of plant that is low to the ground or otherwise easy to force (gently) into contact with soil. There’s also a limit to how many pieces you can try to root at a time, since space usually ends up being a concern. This method can also take longer. But if you’ve got time and a little extra room around your parent plant, this is a great way to start new plants. Layering is a great way to turn existing plants into a dense hedge.

Layering works great for propagating rosemary, lavender, thyme, oregano, mint and most other plants that have wide, flexible stems. It’s not a good choice for plants with very rigid, upright stems or plants that are large and leafy.

While it’s often easiest to bury the section in the ground, you can also put a pot full of soil next to the parent plant and bury the section in that.

rosemary shrub laid over before being covered in dirtthe stripped rosemary twig is buried to make roots


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HOW TO PROPAGATE PERENNIAL HERBS BY DIVISION:

This is the most violent way of making more plants but it’s also very effective!  One simply takes an existing plant and splits it into chunks. The chunks get planted in new holes. In no time at all, each split piece of plant will grow and become a new, full-sized plant.

The other methods can be used on younger plants, but a plant should be mature and well-established before being divided. For most plants, that means at least two full growing seasons. The parent plant needs to have ample, healthy roots and foliage in order to survive the process.

Seasonal timing

Division should be done only at the beginning of the growing season or the very end. It’s very stressful for the parent plant, so it’s best to avoid extreme temperatures.

If possible, plan to divide and plant your perennials just before rain. The cloudy sky and extra moisture can help them recover and establish.

How to divide perennials

Most of the time, you have to dig the parent plant up completely, even if you intend to leave part of it in the same spot. Once it is unearthed, use a sharp shovel, shears or a knife to cut the root system in two. Some plants with softer growth and roots can be pulled apart, but older, tougher plants will require a tool.

The goal is to separate the plant quickly and cleanly, with the least amount of damage to the roots. Some roots WILL end up severed or damaged, but the majority need to survive intact in order for the plants to survive. Work quickly. The longer the plants are out of the soil, the harder it will be for them to recover.

It’s best to divide plants early in the day when temperatures are mild. All of the plants need to go back into soil as fast as possible, so dig the planting holes or fill the containers before you dig up the parent plant.

Planting the new sections

Dig a hole that is large enough to accommodate the entire root ball. If your soil is very compacted or heavy clay, loosen the soil around the planting hole. If appropriate for the plant in question, work in compost or organic matter before adding the ne plant.

Quickly, but carefully, put the section into the hole, fill solidly with soil and then water thoroughly. Even if it’s raining, give the new plant water. It will settle the soil around the roots and help the plant recover.

Keep the new plants watered the first week or two. Division is very stressful for plants and stressed out plants can’t tolerate dry conditions or harsh weather the way other plants do.

large chive plantchives split into two plants

The soil needs to be firm around the roots but not compacted – simply filling the hole thoroughly and then pressing with your hands should be sufficient. The water will ensure the soil settles around the roots and will help the plant recover. Even if the ground is wet or it’s raining while you’re planting, you should water the new plants in their holes!

What happens after re-planting

Once the plants have been divided and planted, they’ll need to be carefully monitored. Don’t be shocked if they collapse limply within a couple of hours. Being dug up, severed and reburied takes a lot of out of a plant! Within a day or two, they’ll perk back up, provided you keep them watered and avoid doing this in hot weather. If you are dividing plants at the end of the growing season, sheer back the top third of new growth before you dig the parent plant up. A haircut means there’s less foliage for the plant to support while its roots recover from the indignity of being cut and replanted.

What’s great about dividing plants is that you immediately double your plants, at least. Very large plants can be split into three or four new plants, but the parent plant should several years old and have a substantial root system. Each new plant need to have good roots and plenty of leaves to survive the process, so if you’re in doubt, it’s better to divide into fewer new sections.

Thyme, oregano, chamomile and mint all respond well to division. Shrubby herbs like lavender and rosemary do not.

Which method of propagating perennials is best?

There’s not a clear winner. Knowing how to use each propagation method will give you the most options when it’s time to expand your garden. In general, woody plants or shrubs won’t tolerate being divided. Leafy plants will usually rot if you try to layer them. Rooting cuttings is probably the most versatile technique but it’s still not a universal solution.

Some herbs really don’t seem to care how you treat them, they’ll make new roots and keep on going. Others are more delicate or more resistant. And sometimes you can do everything right and the new plant just doesn’t survive. For that reason, it’s always best to have multiple new plants going.

Perennials that root well from cuttings:
  • Thyme, rosemary, lavender, oregano, mint, tarragon, chamomile, basil (technically an annual in most zones, but super easy to propagate), lemon balm
  • hydrangeas, mist flower
Perennials that propagate well via layering:
  • Thyme, rosemary, lavender, mint, oregano
  • Most shrubs or vining perennials
  • Any plant that grows low and wide with soft stems
Perennials that are easy to divide:
  • Thyme, oregano, mint, chamomile, tarragon
  • hostas, coneflowers, black-eyed Susans, most non-culinary mints, lobelia
  • any plant that spreads via rhizomes
How to choose a propagation method

In general, the method you pick will depend on both your preference and the age and condition of the parent plant. Younger plants won’t handle division very well but many older perennial herbs actually NEED to be divided once in awhile for optimal health.

Some herbs are very prolific, like mint, oregano and thyme, so it is very easy to propagate them. Others, like rosemary, need more time and patience.

Propagating via seeds and reseeding

Some perennials are challenging to propagate with any of these methods. They may be very slow growing or resistant to setting new roots and division may kill them. For those plants, propagation at home may be nearly impossible, unless you can start them from seeds.

Many herbs will flower and then set seed. This can be a great way to make more plants, but you should wait until the end of the season or until you’re done harvesting from the plant. Flowering changes the flavor of the herb and often saps the plant’s vigor. The plant will put all of its energy into making flowers, which generally leads to very lanky plants with less foliage.

Letting herbs go to seed is great for annuals and biennials, like basil or cilantro, once they’ve reached the end of their season’s growth.

Flowering perennials can also set seeds but may re-seed too vigorously. If you end up with more volunteer plants than you can keep, dig them up and sell or give them away. You can curb volunteers by deadheading flowers before they go to seed.

bed of oregano and thyme