Depending on your soil needs, applying a liquid and granular fertilizer is perfectly safe.
Many gardeners regularly apply a variety of liquid and dry fertilizers, soil additives, pesticides, herbicides, and fungicides, so take a miniature to make a common-sense plan and check for compatibility of any products that you are using.
Be sure to check the compatibility of the fertilizers. There are so many soil additives and fertilizers that interact to form water-insoluble compounds that can clog or destroy sprayers or irrigation systems.
How To Apply Liquid and Granular Fertilizer Together
Get all your products together and read any product labels.
Do your products require wet grass for application? Do they need to be watered in? Should they be applied in dry conditions?
Start by applying dry products that need to be watered in, followed by liquid products then wait until they have dried to apply any products that require dry times.
Start with dry products rather than sprays to avoid having to walk through the wet grass and transfer the fertilizer to your spreader and clothes.
Applying granular fertilizer to a slightly wet lawn the granules can stick to and potentially burn grass or other green leaves.
Granular fertilizers are slow-release and will release their nutrients over time while liquid fertilizers will make the nutrients available immediately.
Be sure that you are not over-fertilizing by comparing the NPK ratios of each product and using an appropriate amount of each nutrient for your plants and your needs.
Before mixing any garden products be sure to check their compatibility to avoid any unforeseen interactions.
Commercial landscapers often use motorized spreader sprayers that apply dry and liquid products at the same time, so it is well established that it is not catastrophic to apply them at the same time.
A DIY lawn care routine should be as convenient as possible for the gardener which is why it is recommended that you apply wet with watering days and dry as soon as possible.
Granular fertilizers can be labor-saving because they do not need to be applied as often, but liquid fertilizers can be time-saving as they can be applied during regular watering or in conjunction with irrigation systems.
Which Fertilizers are Compatible?
Some garden products can interact and form insoluble compounds that can clog sprayers or create an impermeable layer on your yard.
For example, Epsom salt and phosphorus (found in complete or 16-16-16 fertilizers) combine to create insoluble ammonium sulfate.
There are many more of these interactions that are possible, too many to list.
The best way to find if your products are compatible is to conduct a jar test with your products at the same rate that you will be applying them in your yard or garden.
To conduct a jar test measure all your ingredients in a glass jar and add some water if you have dry components.
Look for any of these changes:
Two Compounds Do Not Mix
Look to see if the compounds mix in the jar. If the products do not mix, apply them well apart from one another.
Products that create insoluble compounds will make sediment at the bottom of the jar when the products are mixed.
Make sure you give the jar time to settle so you can observe this kind of change.
Be sure to use the same concentrations you will be using when you apply the products to the lawn or garden.
If you have two chemicals that react when they are mixed they should not be applied at the same time.
You may see foaming like with baking soda and vinegar, or an unexpected color change. This is an adverse reaction and the products should be applied well apart.
If you do not observe any of these changes you are safe to apply the garden products together. You can apply them in the order that makes the most sense to you in your situation.
Just because two products can be applied together doesn’t mean that they should be. A soil test is the best way to choose what products would support your lawn and garden goals.
Which Is Better, Liquid or Granular Fertilizer?
Choose the best fertilizer for your climate, soil conditions, and plant needs.
Liquid fertilizers absorb more quickly in the soil and they leave the soil more quickly as well. These fertilizers must be applied more often and do not remain in the soil.
Liquid fertilizers are generally recommended to be applied every few weeks while granular, slow-release fertilizers can be applied once or twice a season.
Liquid fertilizer can be faster and easier to apply as it can be applied during regular watering.
Sandy soil is particularly bad at holding the nutrients from liquid fertilizer and gardeners may see better results with a granular formula.
Granular fertilizers are designed to release over the course of a few days to weeks as the grass is watered.
Granular fertilizers are often less expensive and have a longer shelf life than liquid fertilizers making them more accessible for many gardeners.
Fertilizing your lawn or garden can be as complex or simple as you make it. A well-established lawn may not even need regular fertilizing.
How To Tell If I Have Over Fertilized?
When applying multiple fertilizers to a lawn or garden it is easy to over-fertilize.
You may notice the yellowing leaves, browning of leaf tips, or drooping of leaves and grass that has been over-fertilized.
Over-fertilizing can also result in leaf loss in plants or root rot.
If you notice that your fertilizer is crusting on the surface of the soil there is too much there.
A soil test would be a good step to determine if your soil is the cause of your plant problems. A high-quality soil test will give you suggestions for correcting any issues you are seeing.
Some of the symptoms listed above can also result in improperly aerated soil.
How To Correct Over Fertilization
Different compounds stay in the soil for different amounts of time.
Nitrogen only stays in the soil for 4-6 weeks and if your plants have survived the initial burns from too much nitrogen they will likely be ok after the nitrogen leaves the soil.
If you are dealing with a small area of nitrogen burn on a lawn you can remove the dead burned grass, lay topsoil in the area, and replant the area.
Phosphorus (sometimes called potash) stays in the soil for years so it is almost impossible to correct. You will have to dig up and move the plants to a new area.
Overfertilization can only rarely be corrected and almost always requires moving the plants to new soil.
Over fertilization is not only dangerous for the plants, but the water that carries the extra nutrients out of the soil will also enter the water table.
Always read all labels of products that you will be using and do the math to be sure you are applying the correct amounts of each nutrient to your plan.
Consider applying compost to build soil over time. Compost builds soil without the high concentrations that can be damaging to plants and water systems.
If you have plants in a container you can sometimes rinse out the fertilizer without killing the plant.
The repotting will slow the growth of the plant.
Applying Liquid and Granular Fertilizers At the Same Time
There is no harm in using liquid and granular fertilizers as long as the gardener understands the needs of their plants, their soil, and their resources.
Choose fertilizers that will not burn your plants with too much salt or nitrogen.
When selecting products for your lawn use a soil test as a guide as over-fertilizing is expensive and almost impossible to correct.
Be sure to conduct a jar test to be sure there are not any reactions between the compounds that could adversely affect your soil or plants.
When the products are mixed in small quantities they should not react or create any sediment.
Watch closely for signs of over-fertilization like yellowing grass, brown tips on leaves, or a crust on top of the soil.
Be aware of any conditions that are required by the various products you will be using in your garden.
Soil temperature ranges are important to get the best results with each product that you are using.
Many fertilizers designed for lawns also contain herbicides that need to be applied before the weed seeds germinate.
There are a lot of factors to consider when combining products, but it can be done safely!