Just because you have a large hill on your property doesn’t mean you can’t plant and care for trees. However, it can feel overwhelming if you’ve never planted or cared for trees on a slope. You must do things differently to ensure your trees survive and remain healthy.
You can plant and care for trees on a slope by making a planting shelf. Dig into the side of a hill and create a flat surface for planting. Water the trees, apply mulch around them, and perform a soil test before adding fertilizer. Remember to prune the trees and maintain the landscape around them.
There’s a lot to learn about planting and caring for trees on a hillside, so I’ve made sure to include everything. Once you’ve finished reading, you’ll know how to build a planting shelf and care for your trees. Let’s begin!
1. Make a Planting Shelf for the Trees
Before you can even plant the trees, you’ll need to build a stable planting shelf. Otherwise, the tree’s roots can spread up the hill, where they’ll be too deep in the soil to survive.
The planting shelf also makes a flat area for the trees, which will make your property look nicer and allow the trees to thrive.
Once you learn how to make a shelf on your hillside, you can also plant flowers and shrubs using the same method.
How to Make a Planting Shelf
Follow these steps to make a planting shelf on any kind of slope:
Inspect the Soil on the Slope
Dig into the ground where you want to plant the trees. Look for fertile soil and a layer of rock or gravel underneath. If the earth’s too dry and crumbly, it won’t hold onto the trees well, and the roots will struggle to establish themselves on the hill. The ground should also be well-draining, meaning it’s not squishy or soaked when you dig it up.
Check the Sunlight
See how the sun hits the slope during the day. You want to plant on the side that gets more sun, so your trees can get enough light. If there are a lot of brown patches in the grass on the hill, it likely doesn’t get enough sunshine during the day. It’s essential to monitor the slope over multiple days to get a better feel for how much light it receives.
Select Your Trees Carefully
Some trees do better on specific slopes than others. You must pick one that can thrive in your area’s conditions. Consider the weather and type of soil you have before purchasing any trees.
However, with a quality planting shelf, you should be able to plant a much wider range of trees on hills.
Some trees that grow best on a slope include:
- Maples
- Douglas fir
- White oak
- Monterey pines
- Manukas
Technically, you can plant nearly any tree on a slope and get good results with a planting shelf, but the abovementioned trees tend to do the best.
When choosing trees, you should consider how deep their roots will go. If there’s not a thick layer of soil on the slope, choose trees that have shallow roots. However, it’s usually better to plant trees with deeper roots as they’re less likely to fall over.
Create the Shelf
Dig into the hill at a 90-degree angle so that you have a flat surface to plant on. You want to dig back far enough for a tree to fit. Since some tree species are larger than others, you’ll need to consider how much space yours will need when it’s fully grown. It’s better to have some extra space than not enough.
Stabilize the Shelf
Mound soil on the downhill side of the shelf, then place heavy stones there. The additional ground also gives the roots more room to spread downhill. It also prevents the soil on the shelf from sliding down the hill. You may need to replace the soil on the shelf every few years.
It might seem overwhelming initially, but if you break down building the shelf into those five steps, you’ll have a much easier time making it. Landscapers can also help you through the process if you can’t do it alone.
No matter what, you must have a planting shelf before you move on to the next steps.
Why Planting Shelves Are Necessary
You should plant a tree on a slope with a planting shelf, also called a terrace. The shelf allows the tree to spread its roots naturally through the hill. Without one in place, the roots can become exposed on the sides of the slope, causing the tree harm.
Without a shelf in place, rainfall can slide off the surface of the slope without adequate soil penetration to rehydrate your tree’s root zone. The same can be said when you try to water your tree without a shelf.
The shelf protects the roots and encourages them to grow throughout the flat area instead of through the hill. When the roots grow upwards into the slope, they can become buried under too much soil, which could kill the tree. Conversely, roots that spread too far down the hill can quickly become exposed, which also causes problems.
A large enough planting shelf gives the roots all the space they need to thrive. So, you should only ever plant trees on a slope if you can commit the time and effort to construct a shelf for it. You can always reach out to local landscapers if you don’t think you can do it yourself.
2. Plant the Trees on the Shelf
Once you have the planting shelf set up, you can start planting your trees. It’s best to wait until the fall or early spring to plant new trees.
Transplant shock can be a problem, especially when growing trees on a hillside, so keep an eye out for it. Giving newly planted trees extra care and attention can help reduce the stress they experience.
Follow these steps to plant a tree:
- Dig a hole in the shelf. The hole needs to be about twice as wide as the root ball but not much deeper than it.
- Place the roots inside the hole. You only want the trunk flare, where the roots connect to the bottom of the tree, to be partially visible above the soil.
- If you can’t see the trunk flare, remove some dirt surrounding the trunk.
- Straighten the tree as much as possible.
- Fill the rest of the hole with soil.
How to Prevent Transplant Shock
Transplant shock can be hazardous to trees, but you can prevent it.
Here are a few tips to ensure planting your new trees goes smoothly:
Choose Trees That Are Native to Your Area
Do research online or look around at existing vegetation in your neighborhood. If you see similar species of tree growing naturally nearby, they’re likely well-suited for the climate and soil conditions on your property.
Plant the Trees at the Correct Depth
Transplant shock can occur if trees are planted too deeply or too shallow, leading to poor root health and stunted growth.
Provide Your Trees With Lots of Water
Give the trees plenty of water until they become established. The extra water can help them tunnel their roots through the soil.
Use the Same Soil to Plant Trees on the Hillside
If you use different soil, it can discourage the trees from spreading their roots out further.
Mulch, Prune, and Fertilize the Trees Regularly
Transplant shock can be caused by improper handling and inadequate care of newly transplanted trees. Mulching helps insulate the roots of newly transplanted trees, while pruning is necessary to promote healthy growth as it removes dead or dying branches.
Ask an Arborist for Help
Consider having a professional arborist inspect the roots a few weeks after planting the trees. They’ll let you know if the trees are taking root well. If not, an arborist can help you correct the problems.
I’ve written an extensive guide about fixing and avoiding transplant shock in trees. Don’t miss it: How to Fix and Avoid Transplant Shock in Trees
3. Stake the Trees (Optional)
You may want to use some stakes to support the trees if you’re planting on a very steep slope.
To stake a tree, follow these steps:
- Gently push on the tree’s base. Trees usually wiggle more on one side, which is where you’ll want to put the support.
- Measure about 18 inches (46 centimeters) away from the tree on each side and place tree stakes.
- Drive the two stakes into the ground.
- Tie the tree to the stakes using elastic straps or pieces of soft canvas. Don’t do this too tightly—the tree should still be able to move slightly.
- Distribute pressure from the straps as evenly as you can.
- Remove the stakes after one growing season. So, if you planted in the fall, you take the stakes out in the spring and vice versa. It’s harmful to the tree to leave them in much longer than that.
- Take care not to hurt the roots when you pull them out.
There are many different items you can use to stake a tree, such as wood, bamboo, and steel pipes. If you can’t find anything that’s suitable, you may want to buy a set at your local garden shop or online.
Signs You Need to Use Stakes
Not every tree you plant will need additional support, even when they’re planted on a slope. However, after planting, you can still check that your tree is stable enough. It’s much easier for them to fall over on a slope, especially before having some time to establish their roots.
You’ll know your tree needs stakes if it shows the following symptoms:
- The tree has a small rootball.
- The trunk bends over without support.
- It leans forward down the slope.
Some landscapers also prefer to stake saplings in areas with a lot of foot traffic to attract attention, so they don’t get stepped on.
However, it can be harmful to stake trees when they don’t need the extra support. Leaving the stakes in place for too long can damage the trunk and cause the tree not to grow properly. The ties can also tighten and restrict the tree, hurting the bark.
Depending on the tree, you can avoid this by removing the supports after a single growing season, about six months to a year after putting them in the ground.
So, staking a tree can be beneficial for trees that need more support on a slope, but you need to take care not to leave it in place for too long. If you notice the ties getting tighter as the tree grows, you can remove them.
4. Water the Trees Often
Newly planted trees need more watering than the ones you’ve had on your property for a while. Water encourages the roots to grow, helping trees on a slope become more stable. So make sure to water the trees immediately after planting them.
You’ll want to maintain a regular watering routine to keep newly planted trees healthy. For about two weeks after planting, you’ll need to water the trees daily.
You’ll need to take care not to drown the roots, so you should confirm the soil drains well. If it’s raining a lot where you live, you won’t want to water the trees much, if at all.
Then from week three after planting to week 12, you need to water the trees every two or three days. You want to give the soil more time to dry in between waterings. To encourage growth, water directly over the root ball. Doing so helps the roots spread and reach more nutrients.
Mature and established trees don’t need as much water, so you can reduce your watering schedule to about once per month if there’s enough rainfall to saturate the soil about 8-12 inches (25-30 cm) deep. However, if the weather is consistently dry for several days, you’ll need to water the trees more.
Learn more about watering a new tree with a hose in my article here: How to Water a New Tree With a Hose (8 Tips)
Water a Transplanted Tree Adequately
It’s dangerous to overwater or underwater a transplanted tree. The roots can drown if you keep the soil too moist. A good rule of thumb is to give a young tree 1-1.5 gallons (4-6 liters) of water weekly for each inch (2.5 centimeters) of its trunk’s diameter.
For example, a small tree with a diameter of 2 inches (5 cm) will only need 2-3 gallons (8-11 liters) of water per week. Increase the water volume accordingly as the tree grows and continue to refer to this equation for three years until the tree becomes established.
Note that newly transplanted trees with larger diameters can take longer to establish. Many gardeners use the trunk diameter as an indicator of how many years a young tree needs to fully establish its roots. You can roughly estimate it by multiplying the trunk diameter (in inches) by 1.5.
Still, that’s just an estimate and can largely vary depending on the soil’s moisture retention capacity or drainage. If you use a plant shelf, you can follow the estimate as a guide. However, without a shelf, water on a slope can be wasted as runoff instead of getting to your tree’s roots.
You can tell you’ve been overwatering the new tree if the ground around it is always squishy when you step on it. Like overwatering, underwatering can also be a significant problem for newly transplanted trees. Without enough water, the trees will struggle to build a robust root system, making them less stable on the slope.
5. Apply Mulch to Protect the Roots
Next, you’ll want to add mulch around the base of the trees. Mulch helps to insulate the roots and keep the soil moist. It even deposits more nutrients into the soil as it decomposes.
There are many different materials that you can use as mulch. When applying mulch to trees on a slope, you generally want to use heavier materials, so they don’t blow away. You can also use netting around the base of your planting shelf to keep the mulch in place.
Shredded bark or wood chips are excellent mulches for trees on hillsides. They’re dense, so they shouldn’t slide away. The bark provides the soil with many vitamins and minerals the trees need to grow. Wood mulch also won’t compact much, helping to keep the soil aerated.
How Much Mulch to Use
Depending on the size and species of the trees, you might need to use quite a bit of mulch. However, you don’t want to use too much mulch since it can also alter the soil’s pH level.
Generally, you can apply mulch until it’s in a 3-inch (7.5-cm) thick layer near the base of the trees. You also don’t want to put it up against the trunk because it can cause stem girdling, which can harm or even kill the trees.
Give the trees enough space between the trunk and mulch pile to prevent issues. You should also spread the mulch out flat and circle up to the tree’s drip line.
6. Test the Soil Near the Trees Frequently
Many slopes don’t have a lot of plants dropping leaves to deposit nutrients back into the earth. So, an essential part of caring for your trees is making sure they’re getting enough nutrients from the ground. You must test the soil around your trees often.
A simple soil test kit comes in handy. There are various kits that you can find online and in home and garden stores that are accurate. By testing the dirt, you’ll know what nutrients need to be added to the soil, allowing you to easily choose a fertilizer.
You can accidentally harm the trees if you start applying fertilizers without testing the soil. It’s easy to add too much of one type of nutrient. Fertilizing can also change the soil’s pH, making it harder for the trees to absorb nutrients and minerals from the ground.
How to Perform a Soil Test
Different soil test kits might have varying instructions, so make sure you read the ones that come in your kit first. Most kits come with glass or plastic vials you’ll use to test the soil. There’s also a guide to help you understand the readings.
Follow these steps to perform a soil test:
- Gather and clean your tools: Wash the tools you’ll use so you don’t contaminate the test. You’ll need a plastic container and a trowel.
- Dig holes for a soil sample: Dig several small holes about 6 inches (15 cm) deep in the area near the tree while being careful not to disturb its roots.
- Collect the soil: Remove a portion around the side of each hole and place it in your container.
- Mix the soil: Stir the soil gently to combine it.
- Dry the soil: Spread out some newspaper and pour the soil over it in an even layer. Allow the soil a day to dry.
- Test the soil: Most kits will have you put the soil in the vials, add some water, and then add chemical drops. You swirl the mixture, then dip a pH or nutrient strip inside.
- Check the results: Compare the strips with the kit’s graphs. They should let you know what your soil lacks so that you can add more to the ground.
Watch for Signs of Nutrient Deficiency
You’ll want to know what nutrient deficiencies look like in trees. When you notice these signs, you can perform a soil test and see what your soil lacks. The sooner you catch nutrient deficiencies, the better.
Here are some signs of nutrient deficiencies in trees:
- Dry, crispy leaves
- Leaves becoming lighter and losing their color
- Leaves turning yellow or brown
- Stunted growth during the growing season
- Leaves staying small
- Leaves falling off the tree early
Providing your trees with fertilizer when they seem unhealthy can help them recover. You can also apply fertilizer to boost your tree’s growth during its growing season. The best time to use fertilizers on a tree varies between species, so you’ll need to ensure that you’re familiar with yours first.
Nutrient deficiencies can kill a tree if you let them go for too long. This condition also makes it harder for the tree to resist many diseases and pests, so you’ll want to address nutrient deficiency as soon as you notice it.
Younger, newly transplanted trees might be more susceptible to nutrient deficiencies because they grow quickly. You should test the soil more often immediately after planting your trees on a shelf and do your best to keep a close eye on them until they become established.
7. Fertilize the Soil
After testing the soil, you should know what nutrients are needed to keep your trees in their best condition. Trees usually respond the best to fertilizers that use NPK ratios of 12-6-6, 12-4-8, and 16-4-8 since nitrogen deficiencies tend to cause the most problems with their growth. You can also use any fertilizer with a 2-1-1 or 3-1-1 ratio.
To apply fertilizer around a tree, spread it on the ground evenly under the tree until you reach the drip line. Then, make sure to water the ground well so that the fertilizer can soak into the soil.
You’ll want to fertilize younger trees at least once yearly since they’re growing rapidly and pulling large amounts of nutrients from the ground. Established, mature trees only need fertilizer every other year to remain healthy.
Fertilize the trees you planted on a slope as part of a regular maintenance routine. Your trees will be much healthier and have fuller branches if you do.
8. Prune the Trees
Pruning can help the trees redirect growth from dying, weak branches to healthier ones, which keeps them looking nice. You’ll need to be more careful when pruning trees on a slope, especially if the hill is steep and there’s little space between the hillside and the trees.
Pruning is essential in keeping trees healthy because it removes branches that were taken over by pests, fungi, and diseases. It also can remove decay, preventing it from spreading to other areas of the tree. Pruning encourages trees to produce more fruit and even keeps them looking nice, so many people prefer to do it.
You must know when and how to prune the trees for the best results. Pruning healthy branches during the tree’s growing periods can have adverse effects that make it harder for the tree to grow well.
Prune Only When the Trees Are Dormant
You’ll want to prune trees during their dormant periods. For many species, that means cutting the branches back in the fall and winter. It’s also better to prune during this time because the trees are less susceptible to pests and diseases, giving them time to heal before it warms outdoors.
Pruning during the winter is also less stressful for trees. When you prune during a growing season, the new growth won’t be strong enough by winter, making it more likely to take damage from the snow and ice.
You’ll want to prune trees during the colder months when they become dormant. It’s much less stressful for your trees and can help them grow well during their active seasons.
How to Prune Trees
If you’re going to prune a tree on a hillside, you’ll need to take extra precautions to keep yourself safe:
- Always secure ladders to the tree if it’s tall.
- Never stand on the top few ladder rungs.
- Have a buddy come with you to help keep you safe when you’re pruning high off the ground.
Next, you’ll want to look for certain branches that jeopardize the tree’s health. You’ll want to cut off branches that:
- Are dry, dead, or decaying
- Are infested with pests
- Have an illness that could spread to other branches
- Cross or rub against one another
- Get too close to utility lines (call the utility company if they touch the lines for safe removal)
- Block too much light
You can also remove healthy branches to shape the tree and enhance its appearance.
To remove the branches, you’ll need high-quality pruning shears to cut through the branches without splintering them.
9. Monitor the Trees’ Health
Regular monitoring allows you to catch any issues that arise early. The sooner you can deal with problems, the healthier your trees will be. Monitoring is especially vital when you first transplant trees into the slope since they’ll be under a lot of stress, leaving them susceptible to diseases.
You can perform the health checks yourself or have a professional landscaper look at your trees from time to time.
There are several different health aspects that you’ll want to check as well:
Check on the Leaves
Keep an eye on the leaves since they hint at the overall health of your trees. Well-cared-for trees have plenty of bright or dark green leaves. You’ll need to closely monitor trees with crunchy, brown leaves, as there’s likely something wrong with them.
Unhealthy leaves are most often a sign of stress in trees. They can be a result of underwatering, transplanting, or injury.
During the spring, slowly growing leaves could also point to a lack of nutrition in the soil. Adding some fertilizer around the trees can help, as long as you know what nutrients the ground’s deficient in.
Lastly, you’ll want to watch for signs of insects. Some make their homes in leaves that can even harm the trees. The following can point to pests harming the leaves of your trees:
- Strange changes in the leaves’ color or shape
- Leaves becoming distorted or forming a cup-like shape
- Leaves becoming sticky
- Leaves looking burnt or dry
- Thinning of the overall foliage
- Leaves having bite marks on them
- White cotton spots appearing on the leaves
Inspect the Branches
Check the branches on the tree reasonably often, preferably at least once a week. You’ll want to remove any loose, hanging branches that aren’t connected to the tree since they can pull down healthy branches too.
It’s also good to check for branches that are missing bark since it’d be easier to start rotting, which can then spread to other areas on the tree.
If you find any damaged branches, you can always prune them.
Look for Damage on Trunks
You’ll also need to watch the tree trunk for signs of damage. Some pests have likely moved in if you see the sudden appearance of tiny holes in the bark.
Trees also produce flux when they’re hurt or dealing with an infection, so keep an eye out for any oozing. Damage or fungal infections can also cause discoloration.
Shedding bark can also be due to stress, although it’s normal for some trees to shed occasionally.
You’ll also need to watch for fungi growth along the trunk. It can mean there’s decay in the tree’s base, which could lead to it falling soon.
Check for Healthy Roots
You’ll need to ensure the tree’s roots are healthy, too. The small portion you see above ground should be thick and strong, not soft.
The following are some critical symptoms to watch out for:
- The appearance of holes among the roots and base of the tree can mean that the roots aren’t doing well.
- Fungi growing on the bottom of the tree trunk can also mean the roots are decaying.
- Raised soil on only one side of the tree means it’s starting to lean to one side.
These issues can be dangerous since the tree could fall over. You’ll want a professional to check out your tree and decide whether it needs to be removed.
Trees growing on slopes can sometimes burrow their roots too far into the hill, where they become crushed under the soil. There’s not much you can do about this, so prevention is critical. Giving your tree a large enough planting shelf can deter it from sending roots too deeply into the hillside.
Trees can also dig their roots out of the ground on the shallow side of the slope, exposing themselves to the elements. Usually, these issues are signs of erosion or poor drainage in the soil, causing the roots to seek oxygen above ground. You’ll want to inspect the soil and increase aeration and porosity to encourage the roots to remain underground.
Check Your Trees Regularly
You’ll want to check on newly transplanted trees often, at least a few times per week. However, it’s essential to have professionals evaluate established trees every two years. They’ll check for signs of damage, pests, and disease, then give you steps to correct those health problems.
Since trees planted on a slope are more likely to fall over, you’ll need to monitor their health and do your best to care for them. It’s essential to get professionals’ opinions, so you know the trees’ exact health status. Arborists and landscape experts are generally who you’d turn to for help in this situation.
You should also check the trees before planning any landscaping or construction work around them. That way, you know your projects won’t harm the tree and that it’s safe to proceed.
10. Maintain the Landscape Around the Trees
Maintaining a healthy landscape around the trees on your planting shelf will keep them in their best condition. You want to keep the planting shelf flat since it will likely erode with time. Adding more soil on the sloped side every few years should help.
You can also build a tree ring around trees on a slope, and it’ll look outstanding. Many landscapers use either stones or bricks for this project. You’ll also need some spray paint or string, plus a square shovel.
Follow these steps to construct a simple tree ring:
- Use the spray paint or string to create a circle around the tree to create a guide. It should be around the perimeter of the tree’s canopy so that you won’t dig up the roots.
- Dig up the ground along the outside of your guide in an even thickness. You want it to be 8 inches (20 cm) deep, even if the ground slopes.
- Add the first layer of stone or brick to the trench you made.
- Starting on the lower side of the slope, add the following block layer on top of the previous one. It’s important to stagger the blogs to make the ring more stable. That means the gaps between the blocks don’t line up.
- Tap on the blocks with a rubber mallet to secure them.
- Add another layer of blocks and continue tapping them into place. Always make sure to start on the lower side of the slope.
- Stop when you have a height that you want. Your ring will be lower on one side, but the top of the tree ring should still turn out even due to the slope. You can add fertilizer and mulch inside the circle to keep the tree healthy.
Building a tree ring comes with a few good benefits, especially for trees on a slope:
- It can help prevent the soil from eroding and exposing the tree’s roots.
- It creates a space for you to place fertilizer and mulch without running down the hillside next time it rains.
- The ring can prevent grass and weeds from growing around the tree’s trunk.
Tree rings work great as flower beds too, but you must choose plants that can grow in the shade under a tree. Plus, you’ll need to consider that they’ll probably get even less sunlight due to being on the hillside. Some begonias do wonderfully in the shade and can thrive on minimal sunshine.
You also don’t have to use stone blocks or bricks to make the ring; large rocks or cement blocks can work well, too. You’ll want to consider what material will work best for you.
Overall, you’ll need to do your best to maintain the landscape around the tree. You wouldn’t want the roots to become exposed, as this can cause severe harm to your tree.
Conclusion
You can plant and care for trees on a slope by creating a planting shelf. The shelf creates a flat, stable environment for your trees to grow. By regularly watering, mulching, and fertilizing the trees, you can help them thrive.
Pruning and monitoring the trees are also essential. You want to catch any signs of disease or damage early, so you can efficiently deal with them. Trees can look beautiful on a slope as long as you care for them!
