Garden Projects

Brrrr, cold nights ahead!

get out the frost cloth!

December 5, 2009

This reddish-pink hebe (2006-2008) pitched it last winter. Probably, no amount of mulch would have helped it – it simply wasn’t a sufficiently cold-hardy plant.

Remember the big freeze last year? The Portland area saw icy winds and temperatures in the teens and low 20s for days on end. I don’t know about you, but I lost a few plants: a voluptuous reddish-pink Hebe and a wonderfully weird Echium pininana which would have sent up a columnar, 10’ tall purple flower spike this past spring had it survived. I do realize that destruction is part of the rich tapestry of life in the garden… but it would have been nice to see them grow and flower this past summer.

Chances are, you already know that Portland’s climate sits within USDA hardiness Zone 8 (Sunset hardiness zone 6). The metro Portland area includes several zones including USDA Zone 8a (average annual minimum temps of 10-15F) and USDA Zone 8b (average annual minimum temps of 15-20F). So depending on where you live, you may have more or less need to protect tender plants.

If the plants in your garden survived last year outdoors, they are likely to survive this winter, too. Established USDA Zone 8 plants may show foliar "freezer burn" or die-back but generally their roots are strong and deep enough to carry them through. However, young and potted plants are another matter.

With last year’s weather-related dramas still fresh in my memory, here are a few suggestions for protecting plants if, as currently (Saturday afternoon) predicted, temperatures dip below 20 the next few nights. (The forecast keeps changing slightly so be sure to check.)

#1: water plants well prior to freezing weather. *Note: any fragile ceramic containers shouldn’t be drenched prior to a freeze, as they could crack or spall. Bring ‘em inside or just accept the risk. (I do the latter, unless it’s a very special pot.)

#2: mulch plants listed Zone 8 and planted in 2009. If it is evergreen (holds its leaves in winter), all the more reason to mulch.

  • To mulch, spread a 2-6 inch layer (depending on how anxious you feel) of bark fines, chopped leaves, or compost over the plant’s root zone. If the plant has a woody trunk (like a tree or shrub), keep the mulch an inch or so from the bark. You can buy bags of mulch and bark chips or bales of straw at local nurseries.

Some garden plants I would mulch, especially if planted in the past year or two:

- hardy banana (Musa basjoo_)
- palm tree (unless it survived last winter without cover – then don’t worry)
- most striped or colorful New Zealand flax (_Phormium sp
- anything Zone 8, planted in 2009, and evergreen. The smaller/shallower the roots, the more useful the mulch.

#3: If the plant is evergreen (keeps its leaves in winter), is reputedly touchy about cold OR is very dear to you, take extra precautions to protect the plant’s foliage. Purchase heavy duty frost cloth or Reemay. There are many plant-wrapping techniques. My method requires scissors to cut the cloth, wooden clothes pegs to secure the frost cloth around the plant, and some bricks or stones to hold the fabric around the base of the plant.

Cover a large area of plants with swathes of frost cloth, Christo-like, or wrap individual plants with pieces of frost cloth cut-to-fit. Secure the cloth snugly with clothes pegs so wind won’t blow it open. You can use more than one layer if needed but I usually stick to one. Use a couple of stones or brick to secure the cloth around the base of the plant or tuck it underneath the pot. Note: Don’t even try using plastic trash bags. I’ve seen it and it’s not pretty when you take it off.

You may want to protect some of your container plants. Any containers with USDA Zone 7/8 plants or broadleaf evergreens like, for instance, bay trees (Laurus nobilis_), Australian fuchsias (Correa sp._) or silver spear (Astelia sp.) would appreciate protection if temperatures drop below 20 for any length of time – especially if it’s a windy site.

Usually, the easiest choice is to move a pot into a cool basement, garage or entryway until the freezing weather passes. If the pot’s too large to move, snug the pot against a structure for protection or lean pieces of Styrofoam, cardboard or plywood against the container to break the wind and help insulate. At least, wrap the plants’ foliage with frost cloth. (See above.) If there are a number of plants in a container and you only need to protect one of them, you can sometimes dig the vulnerable plant out and stash it in a bucket in a cool basement or garage. Just be sure to cover the roots with extra soil if they are exposed after digging.

Stay warm!

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