What Is A Gravel Bed: How To Make A Gravel Bed For Trees
By: Teo Spengler
Trees for transplant are removed from their growing siteswith many of the feeder roots left behind. One of the primary reasons treesstruggle after transplant is the lack of a full root system. This is especiallytrue with trees sold “bare root,” without a root ball. One way to stimulatetransplant trees to grow new feeder roots is by using a gravel bed. What is agravel bed? Read on for gravel bed information and tips on how to make a gravelbed for trees.
What is a Gravel Bed for Trees?
A gravel bed is just what it sounds like, a “bed” or pile ofgravel. Trees intended for transplant are planted in the gravel and kept therefor up to six months. They are given water and sometimes liquid nutrients butnot provided any soil.
The lack of soil stresses the trees, which is required sothey can focus their energy on producing more feeder roots to seek nutrients. Thiscreates a new system of fibrous roots that travels with the trees when they aretransplanted and makes it easier for them to establish and the primary graveltree bed benefits provided.
Gravel Bed Information
The gravel bed system of rooting trees has been used forseveral decades at commercial nurseries, municipalities and universities.You’ll also find community gravel beds where cities encourage the use of thissystem by their residents.
Gravel tree bed benefits are many, especially for bareroot trees. These trees are considerably cheaper to buy thanballed-and-burlapped or container trees, and also lighter and easier to handle.
Since the rate of survival after transplanting bare roottrees is lower and their planting season shorter given their lack of feederroots, putting the trees into gravel beds for a few months creates an expandedmop of small roots that reduces establishment failure.
Gravel bed trees have a higher survival rate whentransplanted. That’s why many cities, especially in the Midwest, are creatingcommunity gravel beds that allow them to buy and plant many more trees.
How to Make a Gravel Bed
If you are wondering how to make a gravel bed, you will needto pick a site with excellent drainage and easy access to water. The size ofthe site depends on how many trees you intend to plant there. Permanent ortemporary borders hold the gravel in place.
Pile gravel at least 15 inches (38 cm.) deep, using nineparts of small river rock or pea gravel to one part same. Simply plant thetrees in the gravel.
Timer-controlled drip irrigation or soaker hoses make theprocess easier. Some community gravel beds add surface applied slow releasefertilizer.
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What Is A Gravel Bed: How To Make A Gravel Bed For Trees - garden
Growing Bare Root Trees: The Missouri Gravel Beds.
The Missouri Gravel Bed (MGB) is a method of handling bare root nursery stock in which the plants are placed with their roots in an irrigated bed of gravel and held for up to 6 months before planting. It is not a growing method, but can be used by growers, nurseries, and arborists to extend the planting season and to greatly simplify the handling of bare root stock. It also shows promise as a method for heeling in B&B stock. The key is that root growth in gravel is very fibrous and unlike mulch or sand, very few roots are damaged when plants are pulled from the gravel.
The MGB was developed at the University of Missouri Horticulture Research Center about 1985. In the initial test, 20 - 4' to 6' bare root Washington Hawthorn trees, after 8 weeks in aerated water, survived planting in midsummer. While aerated water grows good roots, it does not provide any support, creating problems in plant handling. The studies since 1986 have used creek gravel as the support and root growth medium.
Over the past 10 years, many species have been tested in the MGB including ornamental pears, redbuds, flowering dogwood, lindens, maples, crabapples and roses. A test at Sherman Nursery in 1994 expanded the number of species to well over 30. The survival of MGB plants has been as good as or better than container grown or B&B materials.
There is nothing high tech about MGB. All that is required is a layer of gravel and a time clock controlled irrigation system. Plants are simply placed with their roots in the gravel, and allowed to grow until time to plant. A surface application of slow release fertilizer has proven effective in keeping the plants green. Plastic Plumbing Products, Grover, MO, has developed a drip irrigation kit designed for a 4' x 25' bed. Modules can be added as needed, depending on the bed size desired. The kit includes a time clock and solenoid valve and all of the required irrigation tubing and fittings.
Municipal arborists may be hesitant at first to buy plants with their roots out in the open. However, the main reason why MGB works so well is that actively growing roots are placed in direct contact with the soil. When plants are removed from the gravel, spraying the roots with water and putting them in a plastic bag is sufficient. The plants should be planted within a day or two. If the top growth is very soft, it may be advisable to wrap the whole plant in plastic. Five or six times as many MGB plants will fit in a car as container plants of the same size.
Layout: The beds can be constructed in 4' x 25' modules using 1/2" gravel with about 10% sand (passing a #10 screen), 14" to 18" deep. Railroad ties or dimension lumber can be used to make the bed look tidy. The drip irrigation lines should be spaced 1 foot apart and running the length of the bed from a header across the 4' width. Emitters (0.5 gph) are spaced every 6" in the line.
Bed Management: Plants are placed in the bed by digging a trench in the gravel and then shoveling gravel back over the roots. It is helpful to wet the gravel before making the trench. Spacing of plants in the bed will depend on the plant size. Staggered rows work well for trees with 6'- 8' trees as close as 16" in the row. Up to 100 trees and shrubs can be placed in a bed.
It is best to get the bed set up by mid April to allow for good root development before the onset of hot temperatures. Until plants leaf out, watering I is not critical. Set the time clock to water two or three times a day for about 5 minutes. When the plants have begun to flush, set the time clock to irrigate about 3 or 4 minutes every hour during the daylight hours. Later, when the growth has slowed, the irrigation frequency can be reduced to once or twice per day. Let the plants be your guide. Slow release fertilizer granules should be applied to the surface of the gravel. Use a rate similar to that for topdressing container stock but apply at monthly intervals.
Planting: When removing plants from the gravel, lay the plants on a piece of plastic and spray them with water. A bundle of five or ten plants can be wrapped up and tied with twine. If the bundle is not opened and kept in a cool place, the plants can be kept for several days before planting. Dipping the roots in TerraSorb gel does not seem to provide any real benefit and may actually interfere with root growth in some cases. It is best to check occasionally and spray the roots with water. Later in the season, after the top growth has hardened, the roots can be placed in a bag and the tops left exposed. Water added to the planting hole is often the only care required as the roots begin taking up water from the backfill soil immediately.
Chris is a Professor of Horticulture at the University of Missouri - Columbia. Chris can be contacted at (573) 882-9630. Plastic Plumbing Products can be contacted at (314) 458-2226.
Reprinted in The Dirt and Website with the permission of Chris Starbuck 4-6-09
13 Design Ideas When Choosing Gravel for Your Garden
Know your gravels
Gravel comes in many sizes and is essentially small pieces of stone.
It can form naturally over time by the action of water on rock, creating the lovely rounded pebbles we associate with beaches and rivers. This is generally known as pea gravel.
It can also be man-made, formed from crushed rock, which makes it angular and sharp, and varying in size from very coarse down to fine grains.
These two types of gravel have some fundamental differences. Pea gravel has a lot of subtle variations in colour, so it will never look flat or boring, whereas crushed stone tends to be more monochromatic.
Pea gravel is also softer underfoot than crushed stone – a consideration for bare feet, children and pets. Crushed stone ‘beds in’ better, whereas pea gravel requires an edge to keep it in place.
Get some samples of gravel before deciding which one is right for your space and also consider the size. Larger pieces add more texture but are less restful on the eye and are harder to traverse. Gravel that’s around 1cm is ideal.
The type, size and colour of gravel you choose can have a fundamental effect on the appearance and feel of your outdoor space, so consider carefully the look you want to achieve, whether it’s simple and serene or bold and modern.
Let it bloom
Gravel is very attractive to self-seeding plants, which revel in the free-draining stone. The result can be a very natural and romantic outdoor space.
Well-laid gravel doesn’t require a weed barrier, which prevents self-seeders from growing. ‘Well laid’ means the gravel should have a firm foundation or sub-base of hardcore, which is then blinded, or covered, with a thin layer of mill waste (finely crushed stone). This layer is essential to bed the gravel so that it doesn’t move around. It also prevents larger stones from the sub-base appearing through the gravel in an unsightly way.
The gravel layer should then be laid quite thinly as a surface layer (with a depth twice its diameter). If it’s too deep, it can become impossible to traverse. If you feel a weed barrier is essential, it should be laid below the sub-base.
If you’re creating a garden on a small budget, gravel is relatively cheap as a surface and, if well laid, can provide a stable base and foil for some pretty patio furniture.