Seattle’s average last frost date is April 20, but with signs of the garden coming to life all around us it’s tempting to ignore that mid-spring date. With a little knowledge a gardener can predict frost and take measures to temporarily protect tender plants. If the sky is clear and the wind is blowing from the northwest, get ready to take action. One simple technique is covering a tender plant with an old sheet. For more frost prediction signs and protection tips go online to A Gardener’s Guide to Frost
Keyword: Cold protection of plants
A Gardener’s Guide to Frost
A good article about predicting frost and what, if anything, a gardener can do to protect tender plants.
Overwintering Ensete ventricosum
I recently purchased an Ensete ventricosum, which I will plant in a large
container. I live in Bellevue. Should I consider this
plant an annual only? Or is there a way I can overwinter the plant, so that I can enjoy it next year? I don’t have a green house. Would it work to bring it into the garage? If I bring a potted plant into the garage, doesn’t it need water and light? Or could I put hay over the container and leave it outside?
I could not find any information that suggested overwintering this particular
plant outside would be successful. In Bellevue, some other species can be
overwintered outdoors, like Musa basjoo, but E. ventricosum is more tender.
Fortunately, I did find several resources about overwintering your plant
indoors, so you may be able to enjoy your plant over several seasons. The
Missouri Botanical Garden information suggests several methods for overwintering
E. ventricosum. Here is an excerpt:
- Bring container plant indoors in fall before first frost and place container
in a large sunny room for overwintering as a houseplant, with reduced water and
fertilization; - If container plant is too large to bring inside as a houseplant, cut foliage
back to 6-8″ in fall after first frost, and store container in a cool, dark,
frost-free corner of the basement until spring, with periodic addition of a
touch of moisture as needed in winter to prevent the soils from totally drying
out; - If container plant is too heavy or too large to bring inside, remove
plant from container in fall before first frost, wrap roots in plastic and store
in a cool, dark, frost-free corner of the basement until spring (foliage may be
trimmed back or left on the plant and allowed to brown up in the normal course)
If you don’t want your E. ventricosum as a houseplant, overwintering in the
garage seems possible. Given that the Missouri Botanical Garden recommends a
basement and the plant will be basically dormant, meaning it will not want much
water or light, your garage will probably be fine as long as it is warm enough.
The Royal Horticultural Society suggests growing it in a sheltered spot outside, or overwintering it in a well-ventilated temperate greenhouse. Another RHS page no longer available online makes these recommendations about temperature:
To overwinter Ensete, our glasshouse is kept at 16 C (61F) by day and 12C
(53 F) at night – at lower temperatures, lifted plants are prone to rotting. The
lower the overwintering temperature, the earlier Ensete should be lifted and
established in their winter containers, and the drier they should be kept
subsequently.
The site of Cool Tropical Plants includes an illustrated tutorial of lifting Ensete for the winter, however, simply notes that the minimum temperature should be 3 C (about 37 F).
Camellia winter protection
How can I protect my camellia shrubs from very low temperatures?
The website of the International Camellia Society has a discussion of camellias and their cold tolerance, indicating that most spring-blooming Camellia japonica and fall-blooming Camellia sasanqua cultivars will survive a Washington, D.C. winter (zone 7, compared to our zone 8), but there is some concern about extreme cold and drying winds, and sudden drops in temperature (see excerpt below on winter protection, from the University of Georgia Cooperative Extension Service):
Winter Protection
Covering a camellia plant provides frost protection but does little good in a severe freeze. If plants are covered with cloth, plastic or paper, prop up the cover so that it does not touch the buds. Put the cover on after the sun goes down and remove it before mid-morning the next day.
There are additional approaches to providing winter protection against plant damage. Maintain good soil moisture, especially just before freezes. Maintain adequate nutrition by following current fertilizer recommendations. Plant in locations that provide moderate winter shade. Select varieties with good winter hardiness.
The article below from the North Carolina State University Extension has a good general discussion of winter protection for camellias.
on protecting plants from frost
I have some newly planted small shrubs and trees which are now in 3 inches of hard frozen snow. Everything was mulched well before it snowed. Yesterday I covered the plants with large inverted plastic pots, sheets, rice bags, and whatever I had at hand. The plants that are completely under pots will get no light. Can they stay in the dark through this entire cold snap (a week to ten days)? I’m not worried they will overheat under the pots,
with the sun so low in the sky, and the temperatures so cold, but should I be concerned with lack of light?
I have some personal experience with using just such pots to protect perennials, leaving the pots in place (and the plants in the dark) for a week or more. I would expect your plants to be fine. They will not overheat, though drainage holes help with air
circulation. Sheets and rice or burlap bags are fine as well, though the weight of
snow (in addition to the cold) can damage or break plants. You might want
to check the status of the covers if more snow falls. In addition, your mulching will help protect the roots. If the shrubs and trees are deciduous, they do not photosynthesize in the winter (low light and low moisture levels serve as the limiting factors, in general), so your plants will not suffer from the dark environment in
the short term. If the trees and shrubs are evergreen, they do photosynthesize in the winter, but the process is subject to the same limitations mentioned above. Again, no worries in the short term–frost can cause more damage to most plants than a few days in the dark.
Once temperatures are above freezing (32 degrees F or 0 degrees C)–and don’t forget to
consider nighttime temperatures–you can uncover the plants. Usually our
cold weather doesn’t last too long, so I think you can adopt the philosophy “better safe than sorry” and leave the pots in place until you are sure the cold weather has passed.
Below are some helpful links for additional information about predicting
frost and protecting your plants:
- If you are in the Seattle area, Gardening in Washington & Oregon (2005) lists first frosts as arriving “mid-November, earlier in the month to the north and the foothills.”Month-By-Month Gardening in Washington & Oregon
- Cold protection information from Oregon State University
- Frost guidelines from the Farmers’ Almanac
overwintering tuberous begonias
Will Nonstop Begonias overwinter here in Seattle and do well in subsequent years? Mine are in a north-facing shaded area with good soil drainage.
According to the Sunset Western Garden Book (2007), it is possible but not always easy to overwinter tuberous begonias such as the ‘Nonstop’ series. Most people use pots and bring them into a cool, dry, dark environment (such as a garage) for the winter. Others put tubers in the ground but dig some in fall to overwinter in a cool shoebox full of sand. Sometimes they can survive our Seattle winters in the ground, but that is not a sure thing. For example, neighbors of mine lost their last winter despite a blanket of mulch they hoped would protect them. Freezing weather kills them, and the damp soil doesn’t do them any good either.
tree Peonies winter protection
I have two three-year old Tree Peonies – each in a 30-inch pot. Both have buds – what can I do to protect them from the coming freeze – or will they be ok? The pots are way too heavy for me to move. They are sitting on a blacktop driveway margin. I have no dirt to bury the pots into. Do I wrap them? Would bubble wrap work?
The new one I planted Sunday is covered with an inverted pot – will that be enough?
Your peony (Paeonia) buds will probably be fine, but don’t take any chances!
Protect the pots with bubble wrap and cover the tops with bed sheets or some other cloth. I think the inverted pot over your new plant should be sufficient.
Tree Peonies are quite hardy. The frost would be much more damaging if it came in March or April when plants have leafed out.
Here is an article on predicting frost from Michigan State University.
University of California’s Marin Master Gardeners (now archived) also has useful tips on how to protect plants from damage by low temperatures. Tree peonies are not among the plants most liable to be harmed by the cold.
frost and bulb foliage
Do the many bulbs that are rising up to 8″ out of the ground need to be covered since the forecast has temperatures down to 17 degrees F these next few mornings?
The bulb foliage should be fine as it is. Any flowers, on the other hand will probably turn to mush. If you’re feeling protective or nervous you may want to cover up the foliage with burlap, cloth rags, sheets, etc. Once the clouds come back you can remove the protection.
Here is an article on predicting frost from Michigan State University.
Grevillea and cold damage
I have a Grevillea victoriae that I bought 2 years ago. It’s about 2 ft tall and is in a pot with bagged soil and sand added for better drainage. It hasn’t bloomed much, but it was trying. This year it has a lot of frost damage, and I’m not even sure it’s alive.
When can I expect to see new growth? Should I prune off the damaged areas and cross my fingers?
The usual rule of thumb about winter-damaged plants is to scratch the surface of a branch or stem with your fingernail to see if there is green underneath. If there is, that is a good sign. Then, you should give the plant until late June or early July to show signs of resurgence from the damage. I will include below an entire newsletter item on this topic from Plant Amnesty’s Cass Turnbull:
January 2009 e-mail newsletter: Is Your Frozen Shrub Dead? by Cass Turnbull
“After an extraordinarily cold winter in Western Washington, many garden owners will want to know what to do about the damage to many of our not-completely-hardy shrubs. With many of our broadleaf evergreens, it’s common for their leaves to turn brown or black and eventually fall off. The plants themselves are probably still alive. To check, use a hand-pruner blade to peel back a little bit of the “skin” to see if the cambium layer just beneath is alive (green) and not dead (brown). If alive, it’ll probably flush out with a new set of leaves. So don’t panic if you shrub looks dead. Wait and see. How long? By June you will have an answer.
“By then, those that can put on a new set of leaves will have done so. If you can’t stand the sight of the stricken brown shrub until June, try running your hands along the branches to knock the brown leaves off. Then, the plant might seem to be deciduous, not dead. By the end of August, the final report will be in. Freezing weather sometimes does internal damage that doesn’t show up until after the stress of the summer “drought”. A shrub may look okay through June and July, but then, while it is pumping H2O like crazy trying to keep up with the heat demand in August, some portions can collapse, and you will see die-back. (The non-scientific explanation is my own and may be a little, well, anthropomorphic.)
“Many evergreen shrubs, such as escallonia, that suffer freeze damage, will die from the tip back. These shrubs respond well to radical size reduction which in this case means big ugly cuts to the point of green wood. The plants will “break bud” just below your cuts and many new green-leafed shoots will rather quickly grow out to hide the cuts and provide you with a “new” plant by the end of the growing season.
“Often, (for example, in the case of choisya), branches will split, break or splay flat to the ground due to snow loading. Get your loppers out and whack everything back to 4″ to 6″ off the ground. Yes, it’s really Okay. I promise. I have done this thing many times. As soon as the growing season begins, the majority of cut plants will spring into action. As the renovated shrubs grow up, it is advisable to pinch them back every so often, to encourage branching and thicken them up. ‘Pinching’ means a very light heading, just nipping the end bud of each branch with your fingernails or hand-pruners.”
You may find this link to a Northwest grower of Grevilleas of interest, too.
On another topic, I’m curious about the mixture of potting soil and sand you are using for your Grevillea victoriae. If you were to add sand to most Seattle-area garden soil (which tends to be clayey), you would end up with poorly draining concrete-like soil. I would assume that potting soil which already has perlite or something similar in it for drainage and would not need an addition of sand. Are you planning to move the shrub into the garden at some point? This is a substantial shrub–the mature ones I’ve seen are at least 6 feet tall by the same width. If you can find a place in the garden for it, it might fare better. As you probably know, plants in pots tend to be more vulnerable to extreme cold.
Nagami kumquat hardiness
I live in Redmond, WA and I recently noticed that we have been classified as Zone 8A – 8B instead of 7B. Most sources I read state that year-round outdoor planting for Nagami kumquats is recommended only for Zone 8 and above. What is your take on this? I’ve had a Nagami since November, but it has acted differently from what sources I read indicated. I also have a Meyer Lemon that I bring indoors and it did fine over the winter, but the Nagami shed all its leaves within 2 months starting from January. The peculiar thing was that the leaves shed were all green and healthy, leading me to believe it had entered dormancy. It started to grow new leaves in April, but I’m still puzzled why it entered dormancy in indoor conditions even though the less cold-tolerant Meyer flourished.
Long story short, if the Nagami sheds its leaves every winter, will it ever have enough time to produce mature fruit even if it did survive outside?
If you have any particular kumquat or citrus experts you could recommend, that’d be great! Thanks!
According to a local nursery (Raintree), the Nagami kumquat is hardy to 18 degrees, and may produce fruit here. So if we have a cold snap, as we occasionally do, it may be hard on the tree if it’s growing outdoors–unless you can provide it with protection. A friend of mine has grown kumquats before, and they produced fruit, but I believe a long period of subfreezing temperature killed her tree one winter/early spring.
Growing Citrus by Martin Page (Timber Press, 2008) says that kumquats (Fortunella japonica or synonymously Citrus japonica) are prone to zinc deficiency which results in smaller leaves and shorter shoots. They are considered very hardy, but this may be “due to their long winter dormancy.” Nagami grown in a pot will reach about 4 feet, but outside, it can get to 13 feet tall. Fruit is harvested October to January.
It’s possible your Nagami kumquat dropped its leaves because it was entering dormancy, but there are other causes to consider as well. According to the source cited above, leaf drop in citrus trees can be caused by:
- sudden environmental changes (temperature, humidity, etc.)–bringing a plant inside to overwinter is likely to expose it to dry air
- underwatering (don’t overcompensate by watering a leafless plant because it has no way of transpiring the water without its leaves; prune it the next spring by reducing shoots by about a third of their length)
- overwatering (make sure container drains well; soil that doesn’t drain well can lead to yellowing leaves and leaf drop)
You may want to speak to a local expert at the Western Cascade Fruit Society, or the Home Orchard Society.
Also the nurseries that specialize in fruit trees are good resources:
Raintree