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Archive for the Plants Category

Raised Beds – Pros & Cons

Raised beds are becoming more popular, but do they make sense for the garden? What benefits do they provide? Will they grow more food than convention low beds? Does a raised bed need to have side walls? What is the best building material and soil for raised beds? In this and the following posts I will try to answer all of these questions so that you can make an informed decision about adding raised beds to your garden.

Raised beds with hoops

Raised beds with hoops

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Growing Under Walnut Trees

There is a very common myth that says, “nothing grows under walnut trees”, but that is far from being true. If you have walnut trees in your yard or the neighbors yard, you can still have a very lush garden and grow most things.

Gardening Under Walnut Trees, Garden of Phil Reilly

Gardening Under Walnut Trees, Phil Reilly’s Garden

Walnuts and Juglone

Walnut trees produce a chemical called juglone which is toxic to some plants. All parts of the tree including leaves and roots produce juglone. Rain washes the chemical off leaves and bark onto shorter plants growing below them. When the roots of other plants grow close to the tree roots they also come into contact with juglone. Plants can’t escape this chemical.

Trees related to the walnut, including the English walnut, hickories and pecan also produce juglone, but in smaller amounts.

When juglone contacts other plants, it causes them to grow more slowly. Leaves become yellow and wilt, especially in hot dry conditions. In extreme cases the plant will die either quickly or slowly over a number of years.

Juglone-induced wilting and wilting due to water stress produce similar symptoms. A lack of water results in slow wilting which can be reversed if the wilting is not too sever. Juglone-induced wilting often occurs more quickly, can’t be reversed with watering, at least not in advanced stages, and may only affect part of the plant.

The above description about juglone provides the gardener with the information they need, but it is only part of the story. For a more detailed discussion, including myths about julone – which by the way walnut trees don’t produce – see my other post Walnuts, Juglone and Allelopathy.

Walnut Trees

Growing most plants under trees is a problem because they want more sun to grow properly. One good thing about walnut trees is that their leaflets are quite small in comparison to something like a maple and these provide the ideal filtered light conditions for many shade and part-shade loving plants.

Walnuts, like most trees have extensive root systems. The active growing roots can be found two to three times as far from the trunk as the drip line and since a walnut tree is a big tree, one tree will have its roots in several normal sized backyards. The root growth is also dense, and they absorb a lot of water, making the soil under the tree very dry. This dry soil is the main reason people have trouble growing things.

The growing conditions under a walnut tree are part shade and dry. As long as you select plants that like these conditions you have a good chance at growing them.

Juglone and Allelopathy

Allelopathy is the technical term used to describe a situation where a plant produces chemicals that prevent other plants from growing. Walnuts get all the blame, but many plants do this. Another common plant that shows allelopathic tendencies is garlic mustard, an invasive weed in North America. It injects chemicals into the soil that prevent other seeds from germinating.

How big of a problem is Juglone? Everybody talks about it, but a recent review of the known literature suggests that it may not be as big a problem as suspected. It is true that some seedlings are easily affected by Juglone, but most mature plants can tolerate it or are not affected at all. It is quite possible that a lot of the stories about walnuts, juglone and plant growth are exaggerated and that poor growth is mostly due to the shady, dry conditions under the tree.

There is no doubt that juglone toxicity can be demonstrated in a lab under controlled conditions, but finding proof in the field has proven to be much more difficult.

Reducing Juglone Levels

As with all chemicals, toxicity is related to dose. High amounts are toxic and low amounts are not. If you reduce the level of Juglone in your soil, you will have less toxicity issues even for sensitive plants. How can you lower the levels – short of removing the tree?

Removing fallen leaves, branches and nuts will help. All of these contain the toxin and by removing them, less chemical enters the soil. You don’t have to throw away this valuable organic matter. Composting it will reduce juglone to safe levels. The compost can then be returned to the garden. The reason this works is that microbes in the compost pile digest juglone into safe chemicals.

Increasing the number of microbes in the soil will reduce the juglone levels. You do this by following standard methods for improving soil. Don’t walk on it, add organic matter, mulch, and grow lots of plants. These will all increase the organic level in the soil, and decrease compaction – all stuff microbes love. Happy microbes means less toxic chemicals.

Use Tolerant Plants

It is quite clear that some plants are sensitive to juglone, but most are not affected at all. Selecting the right plants makes a big difference.

Plants related to tomatoes, including eggplants, chiles, potatoes and petunias, are sensitive. Some sensitive ornamental plants include potentillas, lilacs, columbines, lilies, peonies, mugo pines, and various privet shrubs.

Good list of juglone resistant plants.

Keep the gardens well watered.

Gardens Under Walnut Trees

If you would like to see a special garden that is grown under walnut trees have a look at Phil Reilly’s garden which was discussed in The Garden Professors Facebook Group. Proof positive that you can have a great garden under walnut trees.

Gardening Under Walnut Trees, Garden of Phil Reilly

Gardening Under Walnut Trees, Phil Reilly’s Garden

References:

  1. Black Walnut (Juglans nigra) and Allelopathy; https://www.ces.ncsu.edu/fletcher/staff/rbir/blackwalnutcompanions.html
  2. Landscaping and Gardening Around Walnuts and Other Juglone Producing Plants; http://extension.psu.edu/plants/gardening/fact-sheets/trees-shrubs/landscaping-and-gardening-around-walnuts-and-other-juglone-producing-plants

Yucca glauca

Yucca glauca, by Robert Pavlis

Yucca glauca, by Robert Pavlis

Yucca glauca, an agave, is the hardiest yucca growing from Alberta, Canada all the way to Texas. You will either love or hate this plant depending on your appetite for desert-like plants. I love them for their spiky leaves and fantastic flowers. They are extremely drought tolerant and easy to grow.

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Paeonia rockii

Paeonia rockii, from seed by Robert Pavlis

Paeonia rockii, from seed by Robert Pavlis

Paeonia rockii is a lovely tree peony that should be grown more. It can be difficult to find in a nursery, but those specializing in peonies will have it. The ones pictured here were grown from seed obtained from the Ontario Rock Garden Society Seedex program. The flowers are mostly white or light pink with dark maroon basal flares on the petals. There is some variation in flower form and coloration. One seedling from this group has red leaves in early summer.

The common name, tree peony, describes the woody stems that are produced, but it is probably more correct to call these shrubs, not trees.  They do not need staking.

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Water Lilies: Hardy and Tropical Water Lilies for Ponds

Water lilies (Nymphaea species) are extremely valuable to the pond. They not only look great and flower well, but the floating leaves provide shade, eliminating the light needed by algae. They also provide a hiding place for fish and other water creatures. Water lilies should cover half of the open water space to help maintain a balanced ecosystem. They do best in quiet water, so keep them away from fountains and waterfalls.

Water lily pond at Longwood Gardens, by Robert Pavlis

Water lily pond at Longwood Gardens, by Robert Pavlis

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