Know When It’s Time to Go: Success through Succession Planting

Part of maintaining your garden design may be to rip out that giant lavender you’ve loved for years and replace it with exactly the same thing.

Yes, you read that right.

This more typical formal style border features easy to hedge plants that like more water in summer, with roses and a few perennials sprinkled across the front. The European shrubs will be long-lived with garden water, but the perennials in front will have to be replaced more often.

This typical formal border by another designer features roses and hedge plants like boxwood that like more water in summer, with a few perennials sprinkled across the front. The European shrubs and roses will be long-lived with garden water, but the perennials in front will have to be replaced more often.

Here in California, where we garden with a LOT of perennials and often shorter-lived native plants, many of your garden favorites have a shelf life. There’s really no exact expiration date marked on that lavender, but if it’s been in your garden more than five years and it’s looking tired and woody, that’s because it is.

Tired.

Hakuna matata! No need to rethink your design plan! Just recycle that puppy on the compost heap, and plant a new little 4″ one–usually for less than $5 from your local nursery–in the same spot.

No need for guilt.

This garden features a lot of grasses and perennials. Installed around six years ago, its nearly time for a few of the plants to be replaced.

This garden features a lot of grasses and perennials. Installed around six years ago, it’s nearly time for a few of the plants to be replaced.

There’s a lot you can influence in your garden with applications of Slugg-O or blood meal or sea kelp or what have you, but age is not one of them. Some plants, especially those adapted to the typical summer-wet temperate climate shared by most of the rest of the US,  Europe, and large areas of central Asia, can be very long-lived (like the yews, camellia, and wisteria at Filoli.) Many plants adapted to Mediterranean, summer-dry climates have survived because they have short lifespans and can reproduce quickly. They just keep pushing out flowers until the rain runs out.

Except in our gardens, thanks to irrigation technology, it doesn’t!

That means knowing when to fold is a key part of California gardening. Having appropriate expectations for the lifecycle of your plant makes it easier to part with it–and replace it–when it’s time. And timely replacement can be an important element of maintaining the design of your garden.

How do I know if age is really the problem?

Woody shrubs are generally much longer-lived, as in 10 to 100 years, depending on the plant type. Perennials, generally speaking, tend to have a shorter shelf life, in the 3-10 years range. There’s an exception that I’ll talk about at the end of this rant. So the first order of business is to know WHAT the plant is. If you don’t know what it is, make an effort to identify it so you can establish an appropriate expectation for its typical lifespan.

A number of the wisteria vines trained to the house date to when the Filoli gardens were first planted, around 100 years ago.

A number of the wisteria vines trained to the house date to when the Filoli gardens were first planted, around 100 years ago.

If a plant is being overwhelmed by pests, it’s probably not the right match for its place. Too much or too little water, too much or too little light, or poorly matched soil conditions can all lower a plant’s natural defenses. If it’s wilting, diseased, shows signs of rot, or full of pests, age is likely not the problem. It’s a poor match for its place. Do some research on the problem, or contact someone knowledgeable who can help you, and determine a more appropriate plant with which to replace it.

On the other hand, if the plant has performed beautifully but is now looking woody or hollow in the middle, perhaps still valiantly attempting to bloom on one side, it may just be at the end of its rope. If your perennial shows no signs of infestation or disease, just looks hollow and pathetic, it may just be age, and it’s perfectly appropriate to replace it with exactly the same thing, if you like it!

What can I do to extend the life of my perennials?

Perennials adapted to our summer-dry climate tend to have extended blooming periods, part of why I love them and try to include them in almost every garden I design. In fact, some of them never seem to stop! It might be helpful to think of them as marathon runners in your garden.

Don’t feed them.

Generally speaking, most well-adapted perennials–and especially California natives–do NOT want to be fed. This is like sitting your lanky marathon runner down at the all-you-can-eat Cracker Barrel buffet, where the vegetable of the day is broccoli cheese casserole. These plants are adapted to going days, sometimes weeks, without water during the summer. If you give them a little extra, they’re going to be thrilled and will continue to bloom for you, long past the time when they might naturally have gone dormant. Give them a lot, and they’re going to go into the plant equivalent of a long, untreated late-onset diabetes spiral.*

Cut back the water!

This perennial border includes grasses, lavender, lamb's ear, and bright magenta penstemon.

I designed this perennial border with grasses, lavender, lamb’s ear, and bright magenta penstemon. The best thing this homeowner can do to extend the life of the plants is to monitor the water. No feeding, no amending! And to extend the life of the design, be firm about selectively replacing a plant when it’s time, with the exact same plant.

Watch your plants carefully through mid-spring and early summer. If those tall, waving perennials start to relax to the ground, they’re getting too much water. This is like feeding your marathon runner plate after plate of spaghetti, never letting them run.

Too much water will kill your plants, sooner (rot) or later (overgrowth.)

Eeek! You were being so careful to give them enough! Yes, enough water is important, but it’s probably a lot less than you think.

If you don’t have time to think about your garden water, make sure you have an ET (“smart”) controller with some soil sensors or a weather station to control your watering schedule. Otherwise, your eyes and your fingers are the best judge of plant health and soil moisture. Dial your irrigation timing up or down to respond to the weather and the condition of your plants.

Hold your breath and PRUNE!

At some point, most of them need to be cut back hard (usually right around late February.) This gives them a sort of “reset” signal to respond with renewed growth. In your garden, they’re getting neither the hard summer-fall drought nor the harder winter that might naturally have caused them to shed a lot of their last year’s growth. If you keep watering through fall so they keep flowering, you have to play Nature and give them the bad news about the end of the season, too.

looking at commercial maintenance isn't always helpful, but in this case the crew did a great job cutting the grasses back at the right time for this native planting.

Looking at commercial maintenance isn’t always helpful, but in this case the crew did a great job cutting the grasses back at the right time for this native planting.

You know all those grasses you’re seeing at the mall or grocery store parking lot right now, and you’re thinking, “Wow, what did that poor plant do to receive a Marine recruit haircut like that?” Well, I’m proud of that maintenance crew because they probably cut them back hard enough. Most home gardeners do not. Penstemon, sage, and other perennials that bloom nearly continuously need this reset to spur renewed healthy growth. Most perennial grasses benefit from it, too, although there are a few tender types (like Pennisetum, the one with the little bunny tails) where it’s best to wait until late March when you see plenty of new growth before you whack them.

What about the exception?

There are always exceptions in gardening, and particularly Bay Area gardening!

One “sort of” exception to the “only perennials” rule: there are many shorter-lived California native woody groundcovers and shrubs that like similar treatment. Ceanothus, for example, is really more of a woody shrub, and doesn’t have tall flower stalks that will give you clear signals of overwatering, but the plant (or colony of plants, if a ground cover type) will last much longer with minimal watering. If your garden includes native shrubs like arctostaphylos (manzanita) or Baccharis (coyote bush) make sure you understand their unique requirements.

In a garden setting, controlling the amount of water applied to your plants can be far more important to their health and longevity than any type of amendment or pest control.

These native shrubs also do well being cut back more aggressively than your typical East Coast woody shrub (although not quite marine-recruit style!) What really shortens the life of these shrubs is hedging them! They can be renovated by thinning them from the inside with hand clippers if they haven’t been hedged for too long, but it may not be pretty for a little while.

Questions? Think I’m crazy? Leave a comment, I’d love to hear from you.

*I’m not a doctor or anything, this is just a bad analogy for the purposes of illustration.

What do you think? Let me know!

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