To both the dedicated perennial landscape gardener, and the more casual observer of trees, shrubs and groundcovers, it has shown itself to be a very hard, strange season for perennial plantings here in Colorado.
First, there was the November, 2014 freeze that struck at our Front Range landscapes before trees and shrubs had a chance to harden off fully for the winter. Following this, another sudden freeze on Mother’s Day, 2015 interrupted the budding stages of a number of plants; and then, there was a cooler, wetter-than-normal spring period. This was followed by a period of intense, dry heat through July and most of August.
These climatic factors conduce to intense plant stress. Whole trees, woody shrubs and tender perennials, or significant sections of them, have shown signs of withering and browning much earlier in the season than usual—or have not leafed out, or otherwise bloomed, at all, presenting bare patches along the borders of house lots, and in the trees lining local streets.
The good news is that all of this can be managed proactively, and gradually repaired.
Of greatest importance now, for this time of the year, is a careful cleanup within and around your shrubs and tender perennials, and within your trees. Throughout such a cleanup, you should be asking yourselves the questions of the Integrated Pest Management (IPM) and Plant Health Care (PHC) processes, being careful to: (1) Identify the plant, (2) Identify the pest and/or disorder, (3) Identify the damage or stress, (4) Identify what situations warrant your intervention for management, and (5) Identify what management options can be effective, and when they should be applied.
Let’s look at trees (both small, and large) first; then we’ll move on to woody shrubs; and then non-woody tender perennial plantings such as grasses and groundcovers.
Let’s look at trees (both small, and large) first; then we’ll move on to woody shrubs; and then non-woody tender perennial plantings such as grasses and groundcovers.
For Your Trees: Whether you have seen damage on the trees in your landscape, or not, now is a very good time to look them over thoroughly, noting any limbs or sections which did not leaf out this season, or are holding on to brown, shriveled leaves, or otherwise appear stressed. If necessary, mark branches or sections with some sort of weather-resistant marker, such as vinyl flagging tape, to accurately track the development of any stressed section.
If a branch or section appears genuinely dead, having retained a stressed or withered appearance throughout this season, or is otherwise a hazard to your property in its stressed state, then that branch or section should be pruned out. Ideally, pruning should be saved for when a tree has gone fully dormant for the winter, with February and March being suitable times for pruning, so that new growth is not encouraged late in this current season, which could stress a tree more than it already is.
Fertilizing a tree, especially when it is stressed, is not a good idea at this time of the year. Fertilizers can either stimulate new growth, or burn the roots of trees, or both. This is especially true if fertilizer is applied in excess. Neither of these outcomes are desirable before winter dormancy.
In addition to this, a thorough and ongoing cleanup of any leaves and twigs shed by your tree from around its base is a good idea—particularly if your tree has suffered in this past season from any insect pest, and fungal or bacterial disease. Such cleanup and off-site disposal will prevent the overwintering of both insects and pathogens.
For Your Woody Shrubs: Whether evergreen or deciduous, woody shrubs, as with trees, will respond well to careful observation and maintenance. You can conduct similar marking of dead or stressed branches or segments for ongoing monitoring, or dormant-season pruning, and can likewise undertake aggressive cleanup of shed leaves, or other vegetation, while not fertilizing until the spring season.
Another measure to consider (which is helpful to trees, but perhaps more so with shrubs) is the two-fold approach of amending the soil around the shrubs, and mulching around them. Soil amendments can work to improve the organic matter content of the soil. This improves the soil’s capacity to hold nutrients and water and, consonantly, the ability of the plant to access and take up both water, and nutrients. Mulches assist in reducing wind and water-based soil erosion, and can provide a degree of climate-consistency to the soils beneath them, helping to protect plants from weather shock.
While able to be applied at any time, soil amendments such as a vegetable-based compost can be fruitfully applied now to improve soil organic matter over the winter. Composts containing animal manure or another high-nitrogen source should be avoided, because they could push new growth on the plant which is, again, not a favorable condition this late in the season.
Mulches, especially of chipped wood and bark, can be applied in a 3 to 4 inch-depth layer around the plantings, but there should be at least a 6-inch diameter circle around the main stem, or stems, left clear. This prevents moisture buildup along the bark of woody shrubs (which could cause disease) and, also, prevents ready access to the lower part of the shrubs by insect and rodent pests.
For Your Non-Woody, Tender Perennials: While these may have been the type of perennial to have, visibly, suffered the most under the wild weather swings between November 2014, and now, the good news is that, depending on how long they have been established in the ground, they have excellent potential for resilience, and healthy re-growth.
The primary condition that you should observe with tender perennials is this: Following full death of the top-growth, which signifies that the root system has completed its process of hardening-off for winter conditions, you should remove all of the old, dead foliage. This is especially important if (as with woody shrubs and trees) your tender perennial was suffering from an insect pest, or a fungal or bacterial disease. If any of this is the case, any and all dead foliage should, as stated earlier, be cleaned up and disposed of away from the plant to discourage the overwintering of insects, or disease.
Too, mulching is also highly important with tender perennials, and a 3 to 4 inch-thick layer around the plants helps with preventing temperature shock.
All of these are, of course, general guidelines covering the broad types of perennial plantings. If you observe your landscape plants carefully, following the principles of IPM and PHC, you can easily construct and implement a cleanup and management plan for your perennials that is better attuned to your specific conditions.
In conclusion, there are two more points I want to leave you with, to inform your plans and practices for carrying your perennials through this coming winter:
- You will still need to water your landscape in the wintertime: This is an art, but does not have to be an intimidating one. You can master it with practice. Your trees, shrubs and tender plants will still need water through the winter, especially during prolonged dry periods, to prevent root damage. Any winter watering should be done at mid-day, on days when air temperatures are above 40 degrees F, so that water will have time to soak in without freezing. More detailed guidelines can be located in the Further Reading resources at the end of this article.
- You will need patience to rehabilitate any damaged or distressed trees, shrubs and non-woody perennials in your landscape: As I previously described, it has been a hard year for perennials in Colorado—to the extent that damage, particularly to long-established perennial plants, may not start becoming visible until well into 2016. And any damage done between 2014 and early 2015 space will need at least 3, to possibly 5, years of recovery time, depending on its severity.
All of this in mind, you can, by patience and diligence, either return your damaged perennials to full health, or ensure the ongoing health of your perennials for a more vigorous and weather-resilient landscape.
FOR FURTHER READING, PLEASE SEE:
CMG GardenNotes #617 Pruning Evergreens
CMG GardenNotes #245 Mulching with Wood/Bark Chips, Grass Clippings, and Rock
CMG GardenNotes #245 Mulching with Wood/Bark Chips, Grass Clippings, and Rock