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Planting Perennials the Right Way

Planting perennials may seem easy but there is more to it than you realize. Planting correctly will ensure larger and healthier plants in the long term.

Acanthus hungaricus - planting perennials the right way, by Robert Pavlis

Acanthus hungaricus with 60 flower spikes – planting perennials the right way, by Robert Pavlis

Planting Perennials the Right Way

You can increase your perennial collection in three ways; germinate seeds, buy potted plants and transplant from either your own garden or a friend’s garden. Most of the information in this post applies to all three cases but the focus will be on potted plants – the kind you get from a nursery.

Nurseries start their plants from either seed or cuttings, but usually from cuttings since so many of today’s perennials are named cultivars which do not come true from seed. These small plants are grown in small pots until they outgrow the pots. They are then moved to larger pots so they can grow bigger. Most perennials are moved several times before they are big enough to meet today’s demand for mature plants.

If this process is done properly, your purchased plant will have a nice fibrous root system that fills the pot with no circulating roots. Circulating roots are the ones found between the soil and pot that go round and round forming the shape of the pot – see the picture below.

Buy Good Plants

This whole process starts with buying good quality plants.

Smaller plants are always a better buy because they transplant much easier and have suffered less time being confined to a pot. Unfortunately, small perennials are rarely sold and you get stuck with a large expensive plant.

Before you buy, turn the pot over, and give it a light tap. The plant should come out of the pot with all of the soil attached, allowing you to have a look at the roots. If you don’t see good white or off-white roots, don’t buy the plant. It was either over or under watered and the roots have died. Or it was just transplanted and you are  paying a high price for a small plant.

I look at roots all of the time in nurseries and nobody has ever told me not to do it. If they did, I would not buy from them. The roots are the most important part of a plant and you need to see them before buying.

If the roots are over grown and circulating a lot, don’t buy the plant unless it is on sale. The plant has NOT been grown properly and now has a problem root system. Why pay full price for a defective product?

The leaves should all be green with no brown spots. A few insect bites are quite acceptable and should not concern you. If it is at the end of the season, and plants are on sale, don’t be concerned about browning leaves. The plant is going dormant for winter.

What About Bare Root Plants?

Bare root perennials will grow well but they are a bit more difficult to establish. If you are a beginning gardener stick to container-grown plants.

Should New Perennials be Flowering?

If your goal is to buy the healthiest plant possible then they should not be in bud or be flowering. A flowering plant is harder to establish than one that is not flowering.

The problem is that most people don’t want to buy such plants – they want to see flowers. So in response to this, nurseries sell large plants in flower.

There is a good reason to buy perennials in flower. Some varieties, like mixed delphiniums, have variable colors and the only way to get the color you want is to buy in flower. Plants like day lilies come in many colors and the color in pictures or online are not always correct. Buying in bloom ensures you get what you want.

A perennial in bloom can be planted successfully, but understand that the plant will have a harder time getting established.

Best Time to Plant Perennials

In colder zones, it is best to plant in spring, earlier is better. Fall is also a good time to plant, but in zone 5, I seem to have less success with fall planting than spring planting.

In warmer zones, try to plant during cool weather.

If you plant during warm weather, understand that the plant will lose water faster. In this case it is a good idea to shade the plant for the first month.

Soil for New Beds

As you will see below, you should not amend the soil in the potting hole before planting. If you are making a new bed, use real top soil. To better understand soil selection have a look at Soil for Raised Beds – Which One is Best?

The Day Before You Plant

Water well the day before you plant. This gives the roots a chance to fill up with water in preparation for the big operation. It is a good idea to immerse the whole pot in water for a 1/2 hour or so, to make sure the center of the root ball is good and wet.

Digging the Hole

Almost every nursery, book and website will tell you to amend the soil before planting. This is usually not required, and can lead to problems. If your soil needs amending, you should amend the whole bed before doing any planting. Once the bed is complete don’t amend each hole separately.

There are two reasons for this advice. First, amending is probably a waste of resources and time. Perennials need to learn how to grow in your native soil. Most organic amendments will soon decompose and the plant will be left in native soil. It might as well get used to this soil right from the start.

The second reason is that an amended hole can have very different watering requirements than the rest of the bed. The hole can be wetter or drier than the rest of your plants. How are you going to water when you have a bunch of different holes all needing different amounts of water?

I grow a couple of thousand different perennials and I almost never amend the planting hole. The one exception is for Clematis which get buried deeper than normal to prevent clematis wilt. My deeper soil is quite poor so I add some compost to the bottom of the hole. The soil around the plant roots is un-amended native soil.

Dig a hole that is big enough for the roots. It does not need to be bigger.

  • Don’t add fertilizer to the hole – newly planted perennials don’t need extra fertilizer.
  • Don’t add stones at the bottom to improve drainage – it does not work.
  • Don’t dig the hole deeper than needed – the plant will just settle too low in the ground.
  • Don’t fork the bottom of the hole to loosen the soil – you want roots to grow sideways, not down.
  • Don’t double dig the bed – a complete waste of time that damages soil structure.

Dealing With Potting Soil

Plants purchased from nurseries are hardly ever growing in soil. Instead, they are grown in some type of peat moss mix or decomposed bark. It is best to remove some or all of this potting mix. If the plant has a good root system you should be able to shake much of it off. You do not need to remove every trace; just get rid of most of it without damaging roots too much.

You can also put the plant in a bucket of water and shake them or wash them off with a hose. Learn more about washing roots in the article Washing Roots Before Planting Trees – which also applies to perennials.

Why remove the potting mix? The advice seems counter intuitive. Why remove this good media and take a chance on damaging the roots? Since this media is all organic it will decompose over the next couple of years leaving the plant with no soil around the roots. While this happens, the plant will sink lower in the ground and may end up buried too deep.

Watering this potting mix is also a problem. Depending on your native soil and the type of mix, the planting hole stays either too wet or too dry. Once dry, peat moss can be difficult to re-wet. I have seen many potted plants where the center of the root ball is completely dry even after heavy watering. The peat moss just does not absorb the water once it has dried.

Removing the potting mix before you plant will help the roots grow more quickly in your native soil, resulting in healthier plants.

Dealing With Root Bound Perennials

Root bound perennials need to have roots cut so they stop circulating around the root ball

Root bound perennials need to have roots cut so they stop circulating around the root ball

Root bound plants with circling roots need special treatment. If you plant the roots the way they are, they will tend to continue circling themselves and not reach out to the native soil, causing nutrient and water problems.

Make four vertical cuts about ½“ deep. If the bottom of the root ball has a lot of tangled roots, just cut the bottom ½“ off.

Shake out as much of the potting mix as you can.

Planting Perennials

Lower the plant into the hole and try to spread out the roots so they are all pointing away from the center of the plant. Make sure the plant is no deeper than it was in the pot. Some perennials will get rot in the crown if they are planted too deep.

Fill the hole with the soil you removed. Pat the soil lightly with your hands, but do not step on it. Roots need air and hate compacted soil.

Mulch around the plant. You can use compost or pine needles, but I prefer wood mulch. Mulch will keep the roots cool and evenly moist.

Watering Perennials

I have dealt with watering in another post; Watering Plants Correctly – When and How to Water.

In short, water well as soon as you plant. Then water when the soil starts to dry out. Don’t water on a schedule – like every two days – that does not work. Touch the soil and water when needed. Too much water kills just as easily as not enough.

It is almost certain that you did some root damage while planting your perennial. The plant will now have trouble getting enough water until it forms new roots. If you understand this, it should be no surprise that newly planted perennials tend to droop their leaves in warm weather. This does not mean they need to be watered. What it means is that there are not enough roots to gather all of the water the plant needs. This is normal and in most cases should be ignored.

More information on this: Water When Plant Leaves Wilt

Removing Buds and Flowers

You now have a difficult choice to make. Do you care more about seeing flowers this year, or having a healthier plant next year? If it is a perennial you should be thinking long term which means you should cut off all buds and flowers at planting time.

The plant has damaged roots and needs to focus water and food (i.e. sugars) into making roots for future years. Don’t force it to also use these resources for flowers.

Is it absolutely necessary to remove the flowers? No. If you don’t, the plant will probably survive. At the very least – don’t allow it to make seed pods. You can also go half and half – leave a few flowers so you can enjoy them and remove the rest.

Should You Cut Them Back?

Common advice for a plant that has already developed a lot of top growth is to cut the stems back to reduce the water stress on the roots. Is this a good idea?

The correct answer is, it depends!

It depends on when you are planting, the amount of the growth, the temperature and the species of plant. When planted early in the season during cooler weather most plants will have less leaf growth and it is not necessary to cut things back. Later in the season when temperatures are high, it can be beneficial to cut some stems back.

If you are planting from a pot, you usually do less root damage than moving a plant from A to B and cutting back is probably not required. When you move an existing plant you cut off the majority of roots and water stress is a much bigger issue. Cutting back is a good idea.

In cooler climates, potted plants can be planted even in mid summer without cutting back.

What happens if you do not cut the plant back and the plant can’t support all of the leaves? Plants will adjust by dropping the excess leaves. To you it will look like the plant is dying. Leaves turn yellow and start to drop. The plant is not dying, it is taking corrective action to ensure that it will survive. It does not need all those leaves, but it does need to make new roots. So it sends all available water and nutrients to roots and ignores the leaves, which then turn yellow. The worst thing you can do at this point is water too much thinking the plant is too dry.

For more on this topic have a look at Transplanting – Should You Reduce Top Growth?

Some leaf die back after planting should be expected. The plant will recover.

When Does It need to Be Fertilized?

Most perennials will grow just fine in most soils without any fertilizer. I grow over 2,000 different ones and none get fertilized, ever.

Fertilize to replace missing nutrients in the soil, not because you think you should do it, or because some book or web site told you to do it. The only way to know which nutrients are missing is to do a soil test. To better understand this basic, yet important point, read this: Fertilizer Nonsense #3: All tomatoes Need the Same Fertilizer.

My approach is to let the perennial grow. Unless it shows signs of nutrient deficiency, I assume it as all the nutrients it needs, and I don’t bother with the soil test. If it grows it does not need fertilizer.

References:

  1. Photo source for Circulating roots (by permission); http://www.rootsimple.com/2014/04/how-to-deal-with-extremely-root-bound-plants/

 

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Robert Pavlis
Editor of GardenFundamentals.com

I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes–I am a plantaholic!


I hope you find Garden Fundamentals an educational site that


One Response to 'Planting Perennials the Right Way'

  1. Susan K says:

    Robert – really great article – good information.

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