Spring in Michigan is always a temperamental time. One day it’s sunny and 70, and the next day it’s snowing. Drop the words “frost free date” anywhere in a Google search and you can get the average date predicting when it’s safe to plant.  The problem with averages is that they come from data on both sides of the average and using this date could leave you frost-burnt as frequently as half the years.

Here at Christensen’s, the full moon in May, or the ‘Flower Moon’ is something we always keep top of mind along with the average frost-free dates. Each spring, we take out our calendars, look for this ever-changing date, and wait patiently. The reason being is that many in our nursery believe that until we are past this milestone, we are still at risk of a frost. Sometimes we get lucky, and this turning point is early, and in other years- like this one, it is late.

The full moon in May was named, as other monthly moons were, by Native American tribes. In regions that were covered in carpets of flowers, the commonly used name of Flower Moon was coined. Other Native American cultures used different names based on what was occurring around them at that time such as Corn Planting moon or Blossom moon. This full moon paired with a clear night has long been believed to bring bitterly cold and unseasonable weather with the threat of hard frosts. The best example of this was the 2020 Flower Moon which brought a cold snap that extended for several days.

Depending on your source, some people believe the Flower Moon is a strong indicator, while others believe it is a long-held myth.  While researching we contacted our favorite local source for all things horticulture, Michigan State University, and asked if they knew of any scientific source that could prove or disprove the moon’s effect on frost. One response was that there isn’t much research on the connection.  Another thought is that it is likely a timing thing – which leads to conclusions that may or may not be able to be proven.

Whether you believe in the Flower Moon or not, we can all agree that, for us in the horticulture industry, a sudden burst of cold weather can be very bad news.  It is dangerous to fresh foliage, buds, and flowering trees.

As you probably know, plants spend the winter in a sleep called dormancy. This dormant period naturally hardens off your shrubs and perennials to withstand the harsh winter temperatures. However, once your plants start to emerge in the spring, we become concerned about colder temps. There are 3 types of freezes issued by the National Weather Service- Frost, freeze, and hard freeze. A frost- sometimes called ‘Killing Frost’ is just frozen dew. Water on the ground, and on the leaves of plants become frozen when temps fall into mid-30s, and winds are calm. A freeze is when temps are at 32 degrees and conditions such as wind prevent the formation of frost. Lastly, a hard freeze is the most serious and occurs when temps drop below 28 degrees for an extended period. It is worth noting that the length of freeze overnight matters. A 1-hour freeze before sunrise is not as worrying as an hours long freeze in the middle of the night. All types of freeze warnings must be recognized, and a plan of action set in place.

The Flower Moon this year is late and will not occur until May 23^rd. If you pair the Flower Moon with the averages that range from May 23^rd to May 27^th, depending on where you are, you will want to watch low temperatures and come up with a plan to combat the frost. Houseplants or potted material can easily be moved inside and out of the cold. In a nursery setting, or in your customers’ yards, here are some tips to mitigate some potential frost damage. At the nursery, we do two main things to battle against frost. Our first method is the continuous running of our irrigation. This frost protection program starts in the wee hours of the morning and runs every 45 minutes for 5-minute spurts throughout the entire nursery. This protects plants by using the heat of the water to continuously warm the plants. Our second mode of action is to use frost protection blankets. These blankets are typically lightweight but effective and do a nice job of keeping the frost from hitting the newly flushed leaves and buds. This method is less practical when talking about protecting an entire nursery, but a very effective plan for flower beds, or to cover smaller groups of our flushed perennials, and Roses. Tucking our plants in before a cold night gives us the peace of mind that they are safe and sound. Some other methods used across the industry are frost fans, under tree sprinklers, keeping grass short to absorb heat, frost protection sprays, and even the use of helicopters to increase air movement.

No matter how you slice it, frost is the arch nemesis of the nursery and homeowners alike. During early spring, it is imperative that we be on watch for cold temps and potential freezes. Whether you can run continuous irrigation, or just plan on using a frost blanket, having a game plan to protect your plants is imperative. Until Memorial Day, we will be keeping our eye on the sky to ensure the best plant material possible!

A special thank you to Michigan State University’s Rebecca Finneran and Keith Mason for help with frost-free dates. MSU is an excellent source for questions on lawns, landscape, gardening and horticulture in general.  You can contact them 24/7 by clicking here. Also, check out MSU’s Enviroweather Tool by clicking here. 

/ˌrōdəˈdendrən/
     noun

First of all, “Rhodys”, Azaleas, and ‘PJMs’ are all the same!!! They are all officially part of the rhododendron genus. They are one of our most popular stars of spring. All of those stocked at Christensen’s are Broadleaf Evergreens, flower in the spring, stay leafed out all year, and start the process over again. (We do not stock deciduous Azaleas anymore but if you need them, we will get you some.)

I also like ‘Boursault’, again another purple flower (heading towards pink). ‘Boursault’ is a Rhododendron catawbiense hybrid and is short. It will reach 5-6’ max. Both are those hardier H1 hybrids.

Last on my list of Rhododendrons is the small-leafed “PJM”. ( FYI: PJM is a series developed by Peter J. Mezitt and his son in the 1930s to be exceptionally winter hardy.) They are getting very hard to find. Sometimes we get ‘PJM’, ‘PJM Elite’, or ‘PJM Regal’. They are all very similar and can work interchangeably. All have the same ‘PJM’ flowers and will reach 3-5’.

In late fall, besides the trees changing colors, you will also notice a change in your perennials. In this article, I would like to discuss fall perennial practices. Topics will include fall cleanup, which perennials should be cut back vs. which should not, perennial varieties that provide habitat for local wildlife, and how we close up the perennial greenhouses in the nursery. These tips should help with the overwintering process.

On the flip side, there are a few arguments for leaving some perennials in your garden alone. To protect the habitats of birds, and beneficial insects, you could consider not cutting Rudbeckia, Echinacea, Eupatorium or perennial sunflower. These seeds will provide food throughout the winter. If your home is close to wooded areas, meadows, or contains a brush pile, your garden may be even more habitat friendly. Some perennials that I would not cut back in the fall would be Asclepias, Ferns, Heuchera, and Dianthus. This is to protect the crowns during the harsh winter. Perennials are more cold-hardy when their stems are left intact. These stems can trap in snow, and work as an insulator for their crowns. A quick clean-up in the spring, and these will be just fine. The last reason why I would consider leaving some perennials be, would be their winter interest. Some stuff just looks awesome covered in snow! Species with stiff stems, or flat or cone-shaped dried flowers have a great winter look! Things like Sedum Autumn Joy, Ornamental grasses, or Echinacea Purpurea add to a garden’s winter beauty!

It is also not uncommon to line an entire house with some of those winter tolerant varieties to both save space, and act as a buffer for other material. We also have one heated structure that we use to protect our grasses (mainly Miscanthus, and Pennisetum varieties), from ever freezing. By keeping minimum heat on our grasses, we are ensuring a healthy, happy grass come spring.

Whether you are overwintering perennials in your landscape, or at your nursery there are many factors to consider. Moisture, temperature, snowfall, and sometimes just plain old luck are all factors that will determine how your perennials fare over a long winter. Keeping in mind potential winter damage, bird and insect benefits, and most importantly, what’s best for the plant, will ensure a seamless transition to the brisk winter days! Happy spring clean ups!

In every lovely garden, there live lovely creatures. Sure, most people wouldn’t find loveliness in critters like slugs and snails. Despite their proven reputation of treating gardens like their personal buffets, I have always been fascinated by them. Let’s face it, they are cute creatures. The leisurely way they move about, the cartoon-like features… there’s something special about them. That being said, they are a pain and can be detrimental to your job site. This article will provide you with some tips on how to keep them away from your plants without harming them.

Slugs and snails are part of the Gastropoda, combination of Greek words gastros (stomach) and podos (feet), under the phylum mollusca (mollusk). Is there a difference between the two? Aside from the obvious shell that differentiates them, not much. Snails tend to be slightly faster than slugs, but other than that, they are quite similar and will eat as much as the other.

While they are notorious garden menaces, they are also helping your landscape as well as feasting on it. Slowly but surely, slugs/snails will break down garden debris and turn it into nitrogen rich fertilizer that enhances soil nutrition (similar to worm composting). Not to mention, albeit a bit morbid, they are a natural food source for other insects and critters such as spiders, birds, frogs, snakes, and toads.

What kind of plants do they like to eat? Anything. They don’t discriminate. However, they usually nibble on the tender leaves and stems of seedlings.

The big question is, what’s attracting them to your landscape? Slugs/snails tend to dry out quickly, so they love wet or damp soil that will keep their jellied mollusk bodies hydrated and happy. If you have incorporated mulch into your job site, that would be another reason why they are taking up residence as mulch tends to retain moisture. Mulch is beneficial for many reasons, so to help with this I would suggest keeping the mulch away from the base of the plants.

Since their main form of transportation is crawling, their sensitive bodies will avoid rough terrain that will irritate their skin. I would suggest creating a barrier around the plants with natural items such as coffee grounds, wood ashes, sand, or eggshells to repel them while simultaneously fertilizing the plants.

Garden debris is a perfect environment for slugs and snails to thrive in, so cleaning debris quickly after the soil thaws in the spring can help. They also tend to lay eggs in debris as well, as it’s a dark, damp, hidden place. If you are dealing with a slug infestation, it is likely that you will find eggs. They are small, jelly-like balls stuck together in slimy clumps. They vary in color but are usually white or translucent. They will typically hatch anywhere from 2 weeks to 100 days depending on environmental factors. Slugs will breed all year round, but peak months of egg laying are from March-April to September-October. To prevent more generations of slugs, rake and turn over soil in areas that have been untouched. Another method is to pour slightly soapy or salty water on identified slug larvae. This will act as a natural poison without harming your plants in the process. You could also simply pick them up using a glove and discard them that way.

While I personally love slugs and snails, not everyone shares the same enthusiasm. If you run into some of our mollusk friends this season, hopefully you find some of these tips helpful to safely discard them from your job sites while maintaining the safety of the plants.

When Does Specializing Turn Into Hoarding?

I’ll just come out and say it. I am a Collector. Over the years I have built - and dispersed – so many collections, in categories such as craft supplies, books, glass paperweights, pink flamingos, Westmoreland milk glass, hardy geraniums, hosta, tools and hardware, office supplies, and for a while in the 80’s, budgerigars. At one point I had 18 of them in a giant flight cage. Good times.

It’s an all-American pastime as shown by the popularity of reality shows about hoarders and people who bid on the undisclosed contents of abandoned storage lockers. I haven’t slid so far; I prefer to do my collecting one piece at a time.

But when does “collecting” cross the line into hoarding? To me, collection is all about doing a deep dive into a particular subject and learning as much as you can about it. When I am studying a new topic, reference books get involved, and talking to experts in the subject, joining Reddits or groups, and getting as much hands-on experience as possible. For instance, I have collected figural cast iron - doorstops, bottle openers, party favors, door knockers and bookends – for years and I am pretty good at spotting reproductions and knock-offs.

When you really love something it’s easy to get caught up into accumulating, and it can be a rude surprise to look around one day and realize there is not one more square inch in your garden to wedge a single additional hosta, even though you are pretty sure you DON’T already have one virtually identical. That’s where we get to the critical difference between a “collector” and a “hoarder”. If you can’t part with your duplicates or lesser-value pieces; the books you’ve read ages ago and won’t look at again, stuff that’s broken or stuff that you MIGHT find a use for …someday… well, now you’re slipping into hoarder territory. News flash: your kids don’t want your stuff. You might want to winnow down your belongings before it gets bad.

I am not quite there yet. Yesterday I spent ten or twelve hours moving all my house plants back indoors after their summer vacation. Somehow there are more of them now than what went out this spring. I don’t know what happened! I have plants all over the house, on shelves and étagères, under lights and crammed into the windows. I am kind of proud of the fact that I also said farewell to a few of them! I am not a hoarder after all. Just don’t ask me how many house plants I have.

Growing and caring for plants is my passion. As if growing tens of thousands of perennials a year here at Christensen’s Plant Center wasn’t enough, I have taken my love for plants home with me. I currently have 20+ houseplants that I care for. The key to success is knowledge and experience. It is important to know what to do, and what not to do. Proper plant care will ensure that your plants thrive, and do not suffer or die (my death count is quite impressive). It has taken years of trial and error to figure out what works best, but I am still learning. If you have any interest in becoming a houseplant novice, this article will provide tips, suggestions, and things to consider.

Houseplants have different demands, requiring individual watering, sunlight, and soil needs. You will want to know each plant’s distinct needs when choosing what to grow. I recommend starting with easy-to-grow houseplants and then move up in skill level from there. My favorite plants to grow are Pothos varieties. These are vining plants that can get very long. Once they get lengthy, they can be “chopped and propped” which means they can be cut into pieces for propagation. To propagate, I cut off a 3-4” piece right below a leaf node (where the leaf meets a stem), place in water, and watch them root. Once rooted, I place them in a pot of soil, fertilize, and watch as they take off. The ability to propagate is one of my favorite features of these plants. Pothos, Snake Plants, Bamboo, Peace Lily, and Spider Plants are among the easiest to grow. While Orchids, Ferns, Fiddle Leaf Fig, Succulents (like string of pearls), and air plants are among the most challenging. Consider how much time, and effort you have and are willing to give to plants at home when deciding what to plant.

Another factor to consider when growing houseplants is watering needs. Some plants can be watered once a week, while others would prefer once a month (or when soil dries out completely). I also like to water my plants on a schedule and mark it on my calendar. I always check the dampness of soil with my finger before adding more water. Overwatering is an easy way to kill houseplants, succulents especially.

Growing houseplants is beneficial to mental and physical health, air quality, productivity, connectedness to nature, and is aesthetically pleasing as home décor. For these reasons, I highly recommend growing and enjoying houseplants in your space. This hobby is something that keeps me happy and busy, and maybe you will enjoy it too.

**Authors note: Husbands/wives/partners/roommates etc. are not always as enthusiastic as you are about turning your home into a jungle. Please keep that in mind when trying to fill every space available with houseplants. Be sure to use the above benefits to try to persuade them! However, compromise might be necessary.
HAPPY PLANTING!!

When I was growing up my father and I planted gladiolus corms in our flower garden next to the house. I remember their bold colors reliably displaying each summer. When I moved into my own home years later I found all sorts of new and exciting colors available. They were beautiful that first year, but the following year I noticed that most of my glads didn’t come back. After some internet-sleuthing I realized that they are supposed to be lifted and stored inside for the winter. So why did they always come back when I was a kid?

Microclimate perhaps? Our main flower garden was against a south-facing brick wall, with years of compost mixed into our sandy soil. Glads don’t like a wet bum, so our native, well-drained soil was a good match. The sun-exposed brick wall warmed up the soil, tempering the chilly winter ground.

Could it have been the heirloom varieties we grew? I’m generally a believer that local heritage varieties are hardier. This seems to be the case with gladiolus. In my experience the new fancy ones, though beautiful, are hit-or-miss with successfully overwintering in our area.

Here are some tips to help you on your way to beautiful spires of color each year:

Plant in pots

Be sure your pots are large and heavy enough so the flowers won’t blow over, also make sure they have drainage holes. Add rocks to the bottom of the pot, top with a sandy soil mix. For an extended blooming season plant pots a couple weeks apart, or mix varieties in the same pot. You can add supports to help the spires stand up as they grow tall. There are shorter, and even dwarf varieties available that may work well in pots without support or the fear of wind damage on balconies. After the flowers are spent it could be a good time to move the pots somewhere less conspicuous, as the plant does not rebloom. Sometime before the first frost, dump out the pots and collect the corms, set them somewhere where they can dry in the open air for a couple days, then lightly cover them up to dry further. For final long-term winter storage place them loosely in layers in a cardboard box, separating layers with newspaper. Keep them in a cool dark place where they may nap until spring, protected from animals and sub-40f temperatures.

Leave ‘em in the ground

With a little bit of luck and some forethought you can have success simply leaving your glads in the ground! Moisture and extreme cold temperatures are what you’re trying to manage. To this end, I have found that digging trenches in sunny areas that are not prone to spring puddling works out well. Planting next to a sun-exposed wall is even better! Dig the trench about 14” deep and fill the bottom 3” with rocks. Mix some native soil with whatever amendments are needed to build a sand-heavy blend with a modest amount of organic matter. Plant the corms at various depths as you fill the trench with soil. I’ve sunk ‘em down 8” with no problems. Hardier varieties such as ‘Violet Queen’ and ‘Atom’, as well as many old heritage classics may help you gain an edge on the colder weather.

Glads will do well with a mulch covering the soil and a balanced fertilizer after emergence.

A recent article by my coworker Matt reminded me of this old saying. It’s born of the experiences of many rock and perennial gardeners. Throughout the years gardeners have collected and experimented with plants, looking for ways to use plants not necessarily accustomed to their soil type or zone. Their answer, in part, was raised rock gardens. Not only aesthetically pleasing, this approach created mini-climates in small spaces much in the same way mountain ranges create dramatic changes in flora from ridge to ridge. Lush forests give way to arid deserts on opposing side of the same mountains.

Rocks and raised beds give plants good drainage. Many perennials in the North die, not from cold, but from excessively wet ground conditions. Perennials such as Dianthus, Lavandula, Gaura, Thymus, et al. thrive in their first plantings only to rot during their juvenile winters. Perennials with long tap-like roots such as Lupines, Hollyhock, Foxglove to name a few die from crown rot due to excessive surface moisture. The fence post problem – solid above and below the ground but rots off right at ground level.

Ground-covering plants like Sedums, Ajugas, Thymus run along filling the crevices, encouraged by the cool, moist conditions. The seed of many annuals and perennials find some of these same places to spend their first winter, where they experience death and rebirth in the stratifying process. A true, natural nursery.

Rocks help ease the stress of extreme temperature change. In the summer they create cool, moist conditions on their down side. In the winter they warm with the sun, giving roots some protection against the cold. Gardeners were often able to include plants that were a zone less hardy. This also works for woody ornamentals that are usually considered sub-shrubs such as Buddleia, Caryopteris, Callicarpa, Hypericum, Crape Myrtle, and more. These types of woodies experience varying degrees of dieback but recover well from roots and heavier wood. Even just tucking hand-sized rocks around the base of perennials and shrubs can give protection and anchor the late-planted.

So when it comes to planting, if you’re ever in doubt, just go get one.

Photos © Holly Christensen, except mountain scene (Storyblocks)

During the COVID-19 shutdown this spring, I was sitting on my porch on what was to be a beautiful day. It was early, and therefore quiet, and I heard a sound coming from my boxwood. I leaned in and distinctly heard what sounded like Rice Krispies in milk. Perplexed, I asked Google what was going on, and Google said, "leaf miners are eating the centers of your boxwood’s leaves". They were making quite a racket. They are either noisy eaters, or there were thousands of them. There was probably no time to lose, so I ignored it. 

A few weeks later I saw the damage to the leaves. They were wrinkling up and turning color. I split one leaf open, and inside were tiny orange maggots, from two to six in every leaf I checked. Now that I could see the little orange bastards, it pushed me into action. I asked google how to deal with them without resorting to pesticides. Google said, "you must resort to pesticides". Particularly, a systemic insecticide that would be taken up by the plant's roots and distributed to the leaves. I applied the systemic, but I was afraid I ignored it too long. They were probably stuffed and pupating and turning into adults. 

Two weeks later, my fears were confirmed. What looked like fat orange mosquitoes were flying in swarms around my boxwood, fornicating and laying eggs in the new leaves. The boxwood wouldn’t survive another generation of these Trump-colored vermin. But I was still loathe to use more insecticide. Hoover to the rescue. I took my vacuum cleaner out on the porch, and began vacuuming the mango scum, much to the dismay of my girlfriend who was awakened by the noise, and immediately questioned my sanity (not for the first or last time). To no avail, I explained my rationale about avoiding the use of insecticides that may harm beneficial insects. Verdict... I was a crazy person. I kept vacuuming. They just kept coming. After a while I went inside to take a nap. 

I woke to the sound of a vacuum cleaner. Yes, outside was my girlfriend vacuuming boxwood. We were both obsessed. This went on for nearly two weeks. The neighbors were too polite or too scared to mention our obsession, but I doubt the boxwood would have survived another season without the intervention, and they look well on their way to recovery. I have to admit though, it was a lot of effort for a few lousy boxwood.

Social Distancing for... plants? Yes, you read that right.

Social distancing for plants has two distinct applications.

The first is to keep plants apart that simply don’t get along well. Examples include those affected by Cedar-Apple Rust such as crabs, hawthorn, and quince and their alternate hosts of Juniper (virginana, horizontalis, and scopulorum). The deciduous get orange spots on their leaves and early leaf droppage while junipers get galls. Similar to this is Pear Rust which affects our ornamental Asian Pears , Bradford, Cleveland, et al. This, too, is caused by over-planting and proximity to Juniper species. The results are similar to Cedar-Apple Rust. A more recent fungal problem exist with our boxwoods and pachysandra. While not alternating hosts, plantings of these as complementary may increase risk of Boxwood Blight. Some genera simply need some distance or even not being included in the same landscape altogether.

The second application of plant distancing is proper spacing. This requires planning and knowledge of plant size, growth rates, and growth habit. The first crime in planting I would call the model home or interior-decorator syndrome. The landscape is planted for the here and now. It has to look lush and lived-in – NOW. The result in a few years is usually a crowded, jungle-like landscape. Much of the original plant material will need to be pulled out. The second crime is a planting that looks nice but really does not reflect the true growth habit of what has been incorporated into the landscape. Remember the Colorado Blue Spruce on the corner of the house; thirty years later you cannot see the house. The development of columnar trees and evergreens has solved this problem. Also, the introduction of many dwarf or compact versions of the old standby varieties has expanded the pool of variety and color palette. Only people my age remember the old Vanicek Weigela (a monster) that yielded to W. fl. ‘Red Prince.’ And now, we have Weigela florida: ‘Wine and Roses, Fine Wine, Dark Horse, My Monet, et al.’ How small can they get?

The art and discipline of plant spacing depends on a great knowledge of plant growth rate and maintainable size. If a new landscape is developing nicely in about three to five years, then you did a good job of placement. Larger trees and evergreens can take around three years to really establish. This is evidenced by greatly increased leaf size and improved coloring in evergreens. From this point on you should see an increase in growth rate. Most woody ornamentals are filling in and exhibit much heavier blooms during this same time. Perennials and groundcovers establish showing very little top growth first season – the Iceberg Effect (roots first, then foliage and flowering the next season).

We are at the mercy of tag information which is far from perfect and landscape architectural drawings rendered by an industry with low plant knowledge. If you take your landscape installation seriously and are interested in long-term results, become familiar with nursery varieties as fast as you can and keep up with new introductions.