Soil, of course, is the natural growing media for perennial plants. That being said, we don’t use it at all in our nursery. There are several reasons for this; the most important is that it tends to hold a lot of water which promotes root disease. Native soil is also heavy which makes moving large numbers of pots more difficult and more expensive to transport. Finally, there’s the issue with weed seeds. Even a small scoop of soil can contain many weed seeds and when you bring that into the greenhouse they grow like mad. We use a soilless mix which bypasses all the negative aspects of native soil. Our custom blended soilless media is composed of finely ground bark, peat moss and other components. It drains very well and keeps the soil pH within acceptable limits. Through trial and error, our soilless mix has proven to be a terrific growing media for our young plants!
In your home landscape, the soil you have is the soil you have. What we’re trying to help you realize is that even if your soil is relatively poor you can still grow great plants. As we begin the discussion, our goal is to help you understand certain aspects of your soil that may negatively affect the growing environment of plants, especially the roots.
From our years in the nursery business, we have found the following to always be true. The top of the plant, that is the part of the plant that you see growing above the ground level, is a reflection of what is happening to the bottom of the plant, in the root zone. If the plant is growing, has good size and is flowering well, you would not expect it to have a poor root system. Conversely, a plant having a robust root system would not have spindly top growth. Oftentimes, if a plant is not growing well, it’s an issue with the roots. Perhaps the soil is being kept too wet or maybe the soil is too compacted to let the roots grow normally. In cases such as these, your first inclination may be to move the plant to another location which is always a possibility. The other possibility is to manage the soil drainage and nutrition to create the best conditions for your plants.
Soil that drains properly is a blessing to gardeners. The vast majority of perennials we grow and sell need oxygen around their roots in order to remain healthy. Soils saturated by water reduce or eliminate oxygen around roots which can create an environment for a variety of soil-borne diseases if not outright drown the plant. Part of your mission as a gardener is to give the plant only as much moisture as it wants. To make this easier we have included the suitable soil moisture needs on each species page. Fortunately, there is a wide latitude with some plants being successful in 2 or 3 different moisture categories. Only a few species are dry only or wet only. It goes without saying that you would not want to plant wet only plants together with dry only plants. We’ve taken the guesswork out of these planting combinations by providing an advanced search feature that will select all the appropriate plants for a specific soil moisture level. Selecting Medium-Dry in the Native Species Search feature will list all the plants we have that fit that soil moisture category. Selecting plants with similar growing conditions will make their care easier for you.
Soil compaction can create drainage problems because water movement through tightly packed soil is more difficult. In your home landscape this can be a problem near the foundation of your home and may even extend out into your yard. When your home was built, heavy equipment was brought in to dig the foundation and to move dirt around. This machinery is very heavy and after repeated passes can compact your soil a great deal. The other, related problem is this: where did all that dirt go that was excavated from your foundation? The subsoil excavated from your foundation is not good topsoil. Instead, it is often a very low-grade, clay-based, subsoil that is of poor quality for growing plants. Its chemistry could very well be wrong for growing plants as well. The final grading of your yard pushed some of this subsoil against your foundation to contour the grade and this is where you’re attempting to plant perennials, shrubs and trees. Any remaining subsoil is often just spread around your yard with that same heavy equipment further compacting the soil. This forms a cap of poor-quality on top of the good quality, original topsoil that is now beneath it. Depending on how thick the cap is your plants may not be able to penetrate through to the topsoil layer. Planting in this clay-based subsoil results in a number of problems because it has few nutrients, no organic material and it holds a lot of water. Fortunately, there are solutions!
Clay is a sticky form of soil material with individual particles measured in millionths of a meter. It is characterized as being a poorly draining soil and is the bane of homeowners everywhere. If we’ve heard it once we’ve heard it a thousand times “we have clay”. The truth of the matter is that many plants are at home in clay and others can tolerate it well. You need to know if the soil you have drains well or needs extra work. An easy way to analyze this is to perform a simple percolation test to see if your ground drains adequately. A perc test involves digging an appropriately sized hole for the plant and filling it with water. Come back 24 hours later and see if the hole has drained. If so, then you’re free to plant. If not, then continue to dig deeper and re-test until you get through this clay cap layer. The idea here is to dig through the clay layer until you get to the topsoil beneath it. The topsoil layer will be a much darker brown color than the yellowish/grayish color of the excavated subsoil. Dig until you see the color change; it’s easy to see. Once you’re there dig a little deeper and break up that topsoil to improve its drainage (remember it may be compacted by the machinery). Perform another perc test just to be sure. Assuming it drains adequately, you probably have a hole that is too deep to properly situate your plants so get a few shovelfuls of topsoil from an undisturbed area in your yard, fill the hole and properly plant your perennial. If you plant in this manner, you’ve created a channel from the surface through the clay and into the topsoil below. This passage allows for water drainage and for root growth into good native soil. Generally, a hole that is twice the size and twice the depth of the pot is a good benchmark for how large and deep the planting hole needs to be.
Soil that does not have adequate drainage creates a difficult environment for plants. It invites a number of root diseases if not outright death due to oxygen deprivation. Repeated compaction causes these problems as it destroys the natural channels in soil that carry water. Simply adding worms to you soil can help recreate those water channels. Adding additional organic composts and wood chips helps to increase microbial activity which promotes healthier soils and provides pathways for excess water to recede. If at all possible, the original soil structure needs to be preserved for best drainage. Compaction does not only come in the form of backhoes and bulldozers. Lawn tractors repeatedly cutting in the same pattern have the potential to damage soil structure.
Soil that drains too well or is too dry can be remedied to create a healthy environment for plant root growth. Incorporating organic material into the soil creates spaces which hold water. The organic material itself acts as a sponge to further retain water. Organic material, in the form of composted leaf mold, wood chips, pine bark chips and sphagnum peat moss (as long as it doesn’t change the soil pH too much) all will improve water retention, and some will add nutrition to you soil. Adding 3-4″of composted mulch or bark chips and tilling that into your soil to a depth of 8-12″ will significantly help. Several authors we’ve researched advise adding enough organic matter to bring the ratio of compost in soil to 1/3 compost and 2/3 soil. This would equate to adding a 4″ layer of composted mulch if you’re tilling to a depth of 12″.
On the irrigation water page, we spend a lot of time talking about water quality because it can directly affect soil quality over time. If you have hard water and have applied it to your gardens for a long period of time it can increase the soil pH to a point where plants are not able to take up nutrition. There are methods available to change the pH of your soil that aren’t difficult to manage. If you decide to apply chemicals or add soil amendments, please note that this is not an overnight fix. It takes time for these changes to take hold and for you to see the desired results. First and foremost, have your soil tested by a reputable lab that specializes in soil and/or water testing so you know what you’re up against. Contact a lab, your county extension office, or your county soil and water people and ask them for recommendations for reputable testing labs. The lab should provide sampling instructions which must be followed carefully in order to get accurate results. Your results will only be as good as the quality of the sample you supply.
One of the easiest ways to lower the pH of your soil is with the incorporation of sphagnum or peat moss. A 1″-2″ layer of peat moss is applied on top of the soil, and it worked in with a rototiller to depth of 6-12″. This method also increases the organic content of your soil which improves its water holding capacity. One of the drawbacks is that it’s an expensive so it works best on smaller beds. Also, this method works best in gardens and flowerbeds prior to planting. Tilling around plants is difficult and usually results in damaged roots.
Nearly everyone has heard of using coffee grounds to lower soil pH. Research indicates that used coffee grounds have a pH that is just slightly acidic, so its usefulness is extemely limited. Coffee grounds would actually work better before they were brewed but that’s just a waste of good coffee.
Adding elemental sulfur is a very safe way to lower soil pH. Elemental sulfur is available at your local garden center in 5 lb bags and is relatively inexpensive. The drawback using this method is that it takes a while for it to work, so don’t expect overnight results. Bacteria in the soil over time convert the sulfur to sulfuric acid which is a strong acid thus lowering soil pH. This conversion only happens during the warm growing season so applying it in the fall and hoping pH will be fixed by spring is not realistic. Apply elemental sulfur in the spring, allow soil bacteria to work during the summer and reassess in the fall. Also, elemental sulfur powder works more quickly than granular forms. The smaller powder particles offer greater surface area for the bacteria to do their job. There are charts available online showing how much to apply in order to make the pH change you want.
Vinegar is another option for lowering soil pH. Vinegar is a weak acid so it’s easy to work with. Adding a cup of vinegar to a gallon of water and irrigating with that can be helpful to acid loving plants like rhododendrons and azaleas.
Aluminum sulfate and iron sulfate also work to reduce pH. Both of these offer a quicker fix, but you have to apply more of it. Read and follow label instructions carefully. Some authors suggest using the iron sulfate in preference to the aluminum sulfate so as not to overload soil with aluminum which could lead to aluminum toxicity.
Fertilizers also offer remediation for lowering and increasing pH. Based on the fertilizer formulation, some react to acidify, or lower soil pH and some react to increase soil pH or increase basicity. It goes beyond the scope of this website to make recommendations about types of fertilizer, application rates and the like but some fertilizers formulations can effectively drive down the pH of your soil rather quickly. Consult with your local soil and water department to see if this can work for you. Have your most recent soil and water tests ready to share with them. Here in the nursery, we were up against some of the hardest, most alkaline, well water known to man. During our initial research for starting the nursery we had a well-known professor from a midwest university tell us we should not move ahead with the business because our water was so poor. Another professor from THE Ohio State University said, “we can beat this”. His solution, after looking at our water tests, was to use the most acidic fertilizer blend available to neutralize the hardness and alkalinity in our water and it worked great! The point here is that our water was exceptionally bad, and we mitigated it. Your water probably isn’t as bad so there’s hope for you!
The above scenario is based on a nursery situation where we water every day, and we fertilize every time we water during the growing season through a drip irrigation system. Your situation at home is similar but not exactly the same. At our home the flowerbeds, potted plants and window box irrigation and fertilization are entirely automated. The expense of such a system is minimal. It is based on the same drip irrigation system we offer here. This system is easy to use, easy to set up and we will offer an online way to customize this to your application.
At the risk of bringing back bad memories from high school chemistry class remember that a change (either positive or negative) in pH of just 1 point is a 10x change in acidity, which is a lot. A reduction in pH of 2 points is a 100x change in acidity. Gradual changes are better tolerated by plants. Please note that the above methods are suggestions. No instructions are provided here because every garden is different, and you should do your own research to find a solution that works best for you. Your final solution may involve several methods.
In certain circumstances it may be necessary to increase the pH of your soil. Earlier it was noted that if soil pH was too high plants would not be able to take up applied fertilizers because these nutrients are bound too tightly to the soil particles. The same is true for low pH. If your pH is too low nutrients are again bound tightly to soil particles and plants cannot use them. Soils naturally become more acidic over time. This is due to a number of factors including leaching by rain. Elements that tend to keep the soil more basic are washed out of the soil profile by rain or irrigation and more acidic components of the soil remain.
Perhaps the easiest way to remedy acidic soils is to lime them. Application of lime serves to increase the pH thus freeing up the bound nutrients plants need. Lime is inexpensive and easy to work with provided you keep it dry. Powdered lime works better than pelleted lime, but the latter is easier to apply through a rotary spreader. Whether you have sandy, loamy or clay type soil also impacts how much lime to apply. Similar to the sulfur application above, liming your soil is not a quick fix but it is safe and effective. There are application rate calculators available online. Check several of them just to corroborate their application rates.
Fertilizers can also be used to increase soil pH. The methodology is exactly the same as using a fertilizer to lower pH except a basic (alkaline) fertilizer is applied. Basic fertilizer formulations, like acidic fertilizer formulations, come in a wide variety of strengths. The tricky part is choosing the right formulation so check with your soil and water department or county extension agent. Have your soil and water test data ready to share with them to save time and to give them an accurate assessment of your situation.
Check with your local state university extension office to see if they offer soil testing. In the past many did offer this service but now many are not. Soil testing by independent labs should not be overlooked especially for well water. The numerous tests performed give an accurate and reliable picture of your soil quality. Armed with this information, you can make accurate decisions about how to best amend your soil to provide the best growing conditions for your plants. The type of test you’re looking for is an irrigation water quality test. You’ll want to get at least the following tests:
Soil pH is important too. If you’ve been watering with well water that you now know is high in alkalinity it may still be affecting your plants. Taking a soil sample to a reputable lab to get it tested is an inexpensive option that will allow you to plot strategy to improve the soil pH if it is amiss. The relatively simple but safe ways to increase soil pH or decrease soil pH described here depend on you knowing your baseline pH so that you don’t make the problem worse. Don’t guess! It’s important to follow the instructions for taking a sample that best represents your soil conditions so follow the accompanying directions carefully.