Pruning Natives Demystified

By: Keith Nevison, Director of Horticulture and Operations

No single task in the garden seems to provoke as much apprehension, drive so many questions, and result in such feelings of satisfaction (if done correctly!) as plant pruning. Artful pruning of plants is something that can take years to master, but the good news is that by following certain guidelines and paying close attention to the plants in your garden, you can get more comfortable with this necessary practice and enjoy it each gardening season.

Why Prune?

Generally speaking, pruning is done to remove the three Ds: deadwood, diseased, and dangerous material. Pruning can also be done to customize shape or tame an overgrown specimen. Here are some examples:

• Tree branches that are crossing or rubbing can put a lot of stress on a plant, so it’s best to remove an offending branch, keeping the strongest, most vigorous shoots or those branches aligned with the desired overall shape.

• When approaching an overgrown or leggy plant, pruning all the way back to basal growing shoots is sometimes the appropriate route and will result in a new lease on life.

• If you’re faced with a tree or woody shrub that is severely overgrown, make a three-year (or more) plan. Remove a fraction of the overgrown material each year. This more patient path can prevent shock and stress to the plant that results from removing so much of its photosynthetic capacity all at once.

When To Prune

A lack of hard frost in many areas of California means that we can get by with pruning later into the season, and tender new growth is at less risk of cold-winter damage. Even still, it is important to consider the seasonality of the blossom cycle when pruning any plant, especially shrubs. As a rule, avoid making any cuts once active growth has started, so as not to cut off flowering potential and prevent awkward “shooting” as the plant tries to recover from injury. Therefore, the best time to prune most California native plants is toward the end of the dormant season, September through December, or before early spring rains cause plants to wake up and grow profusely. Exceptions would be in colder parts of the state (USDA Plant Hardiness Zones 4–9), for specific species, or for pruning out the three Ds. Attend to the three Ds anytime to mitigate risk to plants and damage to humans and structures.

Tools for Pruning

It is important to start with sharp, well-maintained bypass hand pruners aka secateurs. Use any brand you’d like, so long as you keep them clean and sharpened, and they fit your hand ergonomically for comfort and safety. At Santa Barbara Botanic Garden, we are fans of Swiss-made Felco, and these are standard issue for every member of our Grounds Team (and we also sell them in our Garden Shop). Japanese brands like Okatsune or ARS are also solid bypass pruner investments that should last for many, many years through your gardening career. (Please be careful. Carbon-steel blades are super sharp!)

For cutting plant material larger than .375 inches (9.5 millimeters) in diameter, a set of long-handled loppers is a wise purchase that should get plenty of use when tackling trees and shrubs. Bypass loppers typically cut branch material up to 1 inch (25 millimeters) thick with ease, and the longer the handles, the more leverage you’ll have for easier cuts.

For any material larger than 1 inch (25 millimeters), a fine-toothed folding saw is a device that will get plenty of use in the garden, especially when working tree branches that are smaller than necessary for a chainsaw. The saw brand that I prefer is Japanesemade Silky, but there are many quality products on the market. (We also carry Silky saws in the Garden Shop.)

When it comes to chainsaws, our Grounds Team has started moving increasingly toward electric models. These are great when only a few larger cuts are required, or you need to make several small cuts that don’t necessitate the extra horsepower of a conventional saw. The ease of starting an electric saw with a trigger, rather than mixing oil/gas and then pulling the cord to start a “normal” saw, is wonderful and makes one appreciate the advances of modern technological garden tools.

How to Prune (Native) Plants

Most cuts can be boiled down to either tipping or thinning: removing small parts of existing branches or entire branches altogether.

Smaller tipping cuts done during the growing season are typically stimulative, spurring a plant into vegetative growing action. These are the cuts used when shearing a hedge to reduce its overall growing height and to fill a plant out. Here at the Garden, you can see an example of this in our lemonade berry hedge (Rhus integrifolia) that rings the historic courtyard by the Shop and Garden Nursery.

Thinning cuts, by comparison, are made to achieve a desired overall form, getting rid of awkward branches or removing water sprouts that emerge from latent buds after a heavy pruning. When making thinning cuts, it’s important to preserve the branch collar (the band of tissue formed at the juncture of a trunk and its branches) that will eventually grow over the wound, disinviting disease.

Also, one overall tip. When reducing top growth in a tree or shrub, select a lower branch that is at least one-third or greater the diameter of the material above the cut. This helps to prevent premature death or other problems to the specimen receiving the pruning.

Good Techniques Equate To Good Results

Here at the Garden we are hygienic in our approach to pruning, making sure to sanitize all cutting surfaces with a disinfectant to avoid spreading diseases from unhealthy plants to healthy ones. Alcohol (70% or higher concentration) is a good standard disinfectant for disarming most plant diseases and typically doesn’t pose a safety risk to operators, nor tools. Disinfection is important for preventing undesired spread of pathogens like bacterial blights (rose family plants are especially susceptible), rusts, mildews, etc. An easy method for applying alcohol is to carry a small spray bottle with you while pruning, applying whenever you move between plants or more often if working on a particularly diseased specimen.

Pruning Popular California Species

Clearly, California has A LOT of native plant species. The California Native Plant Society lists approximately 6,300 species in our state, with 2,153 endemics (occurring only within our boundaries). To address all possibilities is beyond the scope of this article, but let’s address a few shrubs, perennials, and trees that are common and beloved in our Garden and local environment.

Buckwheats (Eriogonum sp.)

LOVED at the Garden and by native pollinators! These plants are the ultimate summer garden shrub, with a long-lasting floral display that attracts bees and other insects in droves for several months. They also happen to be very easy to care for, with no pruning recommended other than deadheading, but again, this practice takes away seedheads that would otherwise attract songbirds and other creatures. Most buckwheats will not recover after a hard pruning, so go lightly if desired at all. Buckwheats will also self-seed in a garden, especially where a light mulch layer or open soil is present. We think the spent seed heads are attractive in the late-fall garden, so we leave them for wildlife and beauty.

California lilac (Ceanothus sp.)

One of our prettiest native shrubs in spring and a host plant for several types of butterflies and moths. Ceanothus can be trained to become bushier through pinching or lightly pruning in spring, post-flowering. It’s generally recommended not to prune any growth larger than a pencil as it can make plants susceptible to fungal infections.

Manzanita (Arctostaphylos sp.)

Another iconic shrub, found extensively in chaparral ecosystems throughout California and the West. Manzanitas are recommended to be pruned from just past flowering season to early summer. Be aware, that pruning spent flowers will impact the “berry” display and, hence, wildlife attraction to fruits. Don’t prune manzanitas in wet months to avoid spread of fungal pathogens. The Garden’s Grounds Manager Stephanie Ranes offers a bunch of tips on pruning manzanitas: “To promote a denser form or to shape the overall plant, pinch or tip prune in March/April while growth is still tender. Flower buds for the following spring are set in May through June, so if these buds are pruned, the plant will not flower the following spring. Look for new growth without flowering buds or tip only some branches with buds to allow flowering in the following spring. Older plants can be pruned or thinned in summer to reduce their overall size, remove excessive branches, and expose the branching patterns that bring manzanitas fame. Manzanitas heal slowly, so prune carefully into live branches to avoid any unnecessary opening or injury in live material. Make cuts close to the branch without nicking or peeling any bark from surrounding branches. Manzanitas won’t generally recover from a hard pruning, so it’s best to prune or thin lightly every year, if needed at all. Dead branches/wood can be removed any time of year, but make pruning cuts carefully to avoid cutting into any live bark when removing old material.”

Sage (Salvia sp.)

An iconic, aromatic shrub of the West. California sages can be pruned to create a denser habit in late summer/fall by cutting back to one-third or one-fourth of the overall plant. Note that many birds will forage sage seeds, so leaving spent flower stalks (instead of deadheading spent flowers) into summer can be beneficial to wildlife. Stephanie says, “Experimentation in the Garden has shown that even very old Salvia (five to eight years) with very woody stems have succeeded in regenerating after being pruned very hard (most to all of the plant cut back). Regeneration after a hard pruning like this was aided by a deep soaking of the plant and only recommended if the plant has become too large, woody, and leggy to prune lightly. To achieve a denser, more ‘manicured’ form with Salvia, the best approach is to tip prune or pinch new growth at the ends of branches while the plant is actively growing in winter/spring. This technique will affect flowering as Salvia bloom from the end of branches, but it can also help encourage denser growth on the plant overall for future years.”

Sumac (Rhus sp.)

Popular here, occurring in the Garden and in our surrounding environment, including lemonade berry (R. integrifolia), aromatic sumac (R. aromatica), sugar bush (R. ovata), and laurel sumac (Malosma laurina). Many of our sumacs handle pruning well and can tolerate shearing or shaping at any time of year. These plants are highly adaptable, excellent for erosion control as bank stabilizers, and serve as host plants for various lepidopterans (butterflies, moths, and skippers). Lemonade berry is the plant that we have sheared as a hedge in our historic courtyard. Plant one (or several) and have fun!

Toyon (Heteromeles arbutifolia)

One of the most common naturally occurring shrubs at the Garden and our wildlife love this plant. With it putting on an excellent display of “Christmas” berries, it’s best to prune toyon sporadically, if at all, over the course of the year. If a heavy pruning is desired to tame a large, unsightly shrub, it’s best to attempt in late summer, roughly August or September. After any heavy pruning, it’s recommended to give a plant extra water to avoid overly stressing it. Toyon has evolved to crown sprout after fires, but this feature should not be overly tested with aggressive yearly pruning in too short of a time frame, for fear of stressing and exposing to various pathogens.