#050 - 50 Tips Old

And Here’s Another 20 More

First off, apologies this is coming to you on a Wednesday. I was taking a well-deserved break and enjoyed a long weekend at Jacumba Hot Springs on the California-Mexico Border, relaxing in the mineral-rich waters and hiking through the mountains identifying California native plants that were new to me – very exciting!

But in spite of that, we made it to #050. Are you surprised? I honestly am. There are very few things I’ve been able to give this much time and energy to. I’ve enjoyed putting this series together, and we’re not stopping here.

In a weird moment of synergy, just last week my colleague and dear friend Jessa and I put together a planting presentation for our quarterly Design and Technical Excellence Week, and I think a summary of that presentation will serve as a great 50^th post. It pulls together many of the ideas we’ve been circling here on HPT, along with a few more that are directly useful for planting design, especially if you’re working as a landscape architect.

The main point I want to underline is that I’m coming to this with over 30 years of experience working in gardens and 20 years in landscape architecture. Planting design is a specialty that needs that length of time to absorb. You cannot just assume you know how a plant will grow or be maintained, and you have to understand how a mow-and-blow maintenance crew will actually handle a carefully considered palette.

This write-up covers twenty of those practical considerations, drawn from project experience in my home garden, Descanso Gardens, Blake Garden, PWPLA, O|CB, and RIOS. Buckle up, this is a long one. Read a few now and come back later for the ret.

01. You Are a Plant Educator, Whether You Planned to Be or Not

Regardless of how much you think you know about plants, you almost certainly know more than your clients do. Many of them have never worked with a planting designer before and arrive without knowing some of the most important information about plants. You should go over the basics like deciduous and evergreen and talk about how plants get represented in plans and renderings. You’ll also want to find out early whether your client wants color, prefers all-evergreen plants, or has children and pets who will be using the space. These conversations can be straightforward and quick but will save everyone from significant trouble later.

02. Container Size Matters

Even though it may feel like it’s a number on your planting plan, the container size your plants come in carry real cost and performance implications. A fast-growing grass or large shrub installed as a 1-gallon can reach the size of a 15-gallon within a year, while a 15-gallon plant may cost three to five times more at purchase. For fast-establishing species, specifying a smaller container is often the more sensible and cost-effective approach, and in the long run it’s usually a better decision for the health of your plants. Four-inch pots should be a deliberate choice applied where appropriate, rather than a default for groundcover. They establish more slowly and have higher mortality rates than flats, which remain the better choice for most groundcover applications. And for California natives in particular, many species simply are not available in containers larger than 1 gallon, so you should always verify availability with nurseries before specifying, since that may change what you put on your plans.

03. Spacing Depends on the Project Type

Planting spacing on residential projects often operates under a different set of expectations than on civic or public work. Residential installations typically use larger container sizes and tighter spacing, often tip-to-tip with no mulch visible, to achieve immediate visual impact on day one. There is also more flexibility to adjust on the fly, substituting larger specimens and making site modifications in coordination with the landscape contractor. On civic projects, the economics and logistics of scale generally push toward wider spacing and plants that will grow into the design over time. Either way, the spacing conversation with the client needs to happen before installation, along with a realistic discussion of what the space will look like at different points in time, to avoid disappointment.

04. Every Planting Area Needs Irrigation and Drainage

This includes planters. This includes indoor planters. This includes planters under overhangs. Every planting area requires both water input and a path for water to exit if you want your plants to be healthy and happy. This may seem obvious but I will repeat it again and again because it is regularly overlooked in the early coordination of a project, particularly with on-structure projects and interiors. And don’t think you can get away with putting gravel at the bottom of your pots. You still need a hole for drainage. The water will still sit in the soil above the gravel and suffocate your plants due to capillary action. Trust me.

05. Soil Volume Determines Long-Term Plant Health

Available soil volume has the greatest influence on the long-term size and health of plants, and therefore it is extremely important to pay attention to what kind of soil our projects have and how much of it is available. Roots grow in all directions, so connecting planting areas wherever possible, including beneath paved surfaces using soil cells or structural soil, gives trees and large shrubs the opportunity to reach their desired size. We would like to see a minimum 18-inch clear width for any planting area, and that includes pots and planters. We also would like to see a minimum soil depth of 18 inches for our on-structure projects, exclusive of mulch, drainage layers, and topping slab, and even at that depth the plant palette will be mostly limited to shallow-rooted grasses and groundcovers.

06. Light Exposure Has Specific Definitions

The recommended sunlight parameters you see in plant descriptions have actual meanings:

• Full sun means six or more hours of direct sun per day.

• Part sun means four to six hours of sun per day, with mostly midday to afternoon exposure.

• Part shade means four to six hours of sun per day, mostly in the morning.

• Full shade means fewer than four hours of direct sun per day.

These are precise categories, and using the wrong one for a given species is one of the more reliable ways to produce an unsuccessful planting condition. Light conditions also shift over the life of a project as the tree canopy develops, eventually shading out the shrub and groundcover layer beneath it. Clients will benefit from knowing this information in advance, and your clients may return for replacement recommendations for more shade-tolerant species at some point down the road.

07. Read Books

Internet sources for plant information tend to address a wide range of conditions and are written for general audiences, which means the specifics of climate zone, soil type, and regional availability frequently get flattened out. Good books offer more precision, and you can usually find a book that can help you with your exact planting dilemma.

For Southern California work, three that I find myself referencing frequently are:

• Sunset Western Garden Book

• Landscape Plants for California Gardens by Robert C. Perry

• California Native Plants for the Garden by Bornstein, Fross, and O’Brien.

08. Planting Zones Are Binding Constraints

Confirm that every plant you select is rated for your project’s climate zone before it ends up on your plan. Some species can be pushed slightly beyond their rated zones, but that should be a deliberate decision made with awareness of the risk. This is a judgment you must make yourself, and it becomes particularly important in zones where freezing temperatures are possible. Zone compatibility doesn’t always line up with nursery availability: a plant may be theoretically suited to your zone but unavailable in commercial quantities, or simply not grown by any nursery in your region, so check before specifying.

09. Invasive and Toxic Plants Are Your Responsibility to Track

We’ve talked about this before, even though it’s hard to believe: nurseries will sell you invasive plants without informing you. Some cities and counties may maintain invasive and restricted plant lists, and it is worth searching for these before starting work on a project in an unfamiliar jurisdiction, but really it all comes down to you to stop invasives from being planted. In regards to toxicity, levels can range from mild skin irritation to serious harm, and some plants are toxic specifically to certain animals rather than across the board, so you need to do your research. The full scope of plant toxicity is genuinely complex to track, but San Marcos Growers maintains a useful poisonous plants reference at https://www.smgrowers.com/resources/Poisonous.asp , and Theodore Payne Foundation publishes an invasive plants list for Southern California https://theodorepayne.org/invasive-plants/ .

10. Indoor Plants Require Special Attention

Indoor planting typically sits outside the standard landscape architecture scope and in most cases should be contracted separately. In an ideal situation, indoor planting projects are typically coordinated with a dedicated indoor planting maintenance team to support long-term success. You should always remember that the plants we commonly refer to as “indoor plants” actually started as “outdoor plants” that happen to tolerate low light, variable temperatures, and inconsistent humidity well enough to survive indoors. When a project requires plants in spaces without adequate natural light, grow lights are necessary and should be planned for early on in the project, as they are expensive, require careful configuration, and involve MEP coordination. Humidity is another consistent challenge in air-conditioned and heated interiors, and indoor plants are generally more susceptible to pest and disease pressure than those grown outside, requiring weekly or even daily care.

11. Massing Carries More Weight Than Variety

This is the closest I’ll get to an actual design edict in this entire tip, but it’s a design recommendation that goes hand in hand with long term care and maintenance. In most situations, a palette with too many species can dilute the spatial clarity of a planting design. Repetition and massing can create legibility at larger scales, and projects often become more coherent when the plant palette is reduced rather than expanded. There is also a maintenance aspect to this too: when plants of the same species are grouped together, a maintenance crew can move efficiently through a planting area without having to switch approaches for each individual plant. This is one of the reasons civic and public projects tend to use large swaths of the same species.

12. Hydrozones Are a Planning Tool and a Regulatory Requirement

Hydrozones group plants by water need, typically categorized as very low, low, moderate, and high use. These groupings form the basis for irrigation system design and are required under MWELO, California’s Model Water Efficient Landscape Ordinance. Plants within a single hydrozone must share compatible water requirements. This matters for trees as well: Coast Live Oaks and other California natives sensitive to summer water should be sited within low-water zones to avoid overwatering. So make sure your planting plan is designed and organized by water use, and make sure you coordinate with your irrigation designer early!

13. Planting Design Means Designing With Time

One of the first tips we covered is that trees are typically shown on planting plans at 75 percent of mature size, which means spacing decisions need to account for what the planting will become rather than what it looks like at installation. A lesson I learned early on at O|CB is that fast-establishing shrubs and grasses may visually dominate a young tree in the early years of a project, and that same tree may eventually shade out the plants beneath it. On-structure projects add another variable: trees planted over structure often have restricted soil volume and may be required to stay pruned to a certain size due to structural load limitations, meaning growth on structure tends to be slower and more constrained than comparable plantings on grade.

14. Coordination Below the Surface Requires Careful Consideration

On-structure planting requires early coordination with the structural engineer to confirm that tree locations are structurally supported and that there are no conflicts with slabs, beams, ducts, or drains. Soil weight and depth need to be confirmed against structural limits, and ideally lightweight soil composition would stay at or above 100 pounds per cubic foot. Lighter soils have lower organic content, which creates complications with irrigation performance, wetting and drying cycles, and long-term plant health. Underground utilities require clearance compliance on grade-level projects, and utility coordination on-structure tends to be more even more complicated.

15. Irrigation Plans Require Your Active Involvement

The irrigation designer is typically a consultant to us as landscape architects, which means they need to receive updated planting plans and hydrozone layouts with enough lead time to complete their work at each project milestone. Valve boxes and major irrigation equipment need to be located as part of our site design, because if that placement is left to the irrigation designer alone, it will often end up in the last spot you’d ever want it to be. Additionally, irrigation submittals should be sent to the irrigation designer for initial review, and their comments should be reviewed carefully to confirm agreement before they are transmitted to the contractor.

16. Planting Plans Are Legal Documents

A planting plan issued at any stage of design is a contractual document that locks in container sizes, spacing, and often species. Consider this before adding preliminary or placeholder plant symbols to your plans as a last ditch effort before submitting. Releasing a fully-baked planting plan before the rest of the project is finalized typically results in inaccurate cost estimates and design commitments that are expensive to change later. The content of SD, DD, and CD drawings should be carefully calibrated to can actually be confirmed at each phase.

17. Construction Administration Requires Specific Knowledge

Site visits during planting installation are a key part of our work. Look for plants installed too low, flag wrong species as they arrive on site (grasses and deciduous plants are particularly common sources of substitution errors), verify spacing and quantities against the plan, and check that plants are triangulated correctly. You have the right to reject plants and trees that do not match approved submittals. The contractor carries responsibility for plant survival during the warranty period, but attentive observation during installation remains part of your role. Photograph and document each site visit in a field report.

18. Design for the Maintenance Crew You Actually Have

You can’t deny that we talk about maintenance a lot on Hot Plant Tips. A complex and detailed planting palette with many different species will only be able to maintain its design intent if there’s a robust maintenance program capable of supporting it. Where maintenance is limited, a simpler and more forgiving palette is the more realistic choice. Remember that in most projects, plants along walkways will be string-cut back to the concrete edge. Anything likely to be hedged will be hedged. Ornamental grasses will be cut back at some point in the year regardless of what the plan says. If you have specific ideas about how the plants in your design should be managed, you’ll need to produce a maintenance manual, and I recommend walking the site with the maintenance team, with return visits as needed.

19. Plants Die

You can expect to see plant mortality rates of 10 to 15 percent even on well-executed projects. Plant replacement is part of the landscape contractor’s contract, and both the maintenance period and the warranty period have specific durations that should be understood from the start. Schedule a site visit before the warranty period ends to assess what has failed and initiate replacement requests. You must remember that perfection at installation is not a reasonable benchmark.

20. You Get Better With Every Project

You learn from every project you work on, regardless of scale. Going back to a site a year after completion in whatever way possible, whether in person or through Google Street View, will provide important information you cannot get any other way. If you take the time to study your built work, you will learn from both successes and mistakes, and each time you see plants in a different condition, you gain a clearer understanding of how they actually perform.

It takes years to build a repertoire of planting knowledge, and regularly assessing your projects is one of the few ways to accelerate that process. The other thing I can recommend to quickly improve your planting expertise is to work in a garden. If you do not have access to one of your own, there are volunteer opportunities all around you. Digging in the dirt, pruning plants, pulling weeds, and assessing irrigation choices will all help you understand the consequences of design decisions and contribute to better project outcomes.