Feeding your vegetable plants enough nutrients during the growing season is key for abundant harvests. There are both liquid and granular fertilizers and this article covers when to use both.
Your plants don’t just need water to survive and thrive. They also need plant food. And that comes in the form of various fertilizers.
But you’re likely wondering: what plant fertilizers should I use? And are some types of plant fertilizer better than others to use?
Organic vs. Synthetic fertilizers
You’ve maybe grown up with seeing your parents using the blue powder, mixed in water to fertilize plants.
Or some other synthetic concoction of chemicals that provide the three letters N-P-K (Nitrogen, Phosphorus and Potassium). Often these are sold as 20-20-20 on the package to denote the concentration of all these nutrients.
It’s common however to burn your plants if you use too much or if you apply it at the wrong concentrations.
It gives plants a quick shot of nutrients that doesn’t last very long, so you’re having to apply it regularly.
Instead the trend now is towards organic fertilizers that are made from organic, natural ingredients.
The benefits of an organic fertilizer is that it is hard to burn your plants if you use too much. Most organic fertilizer is slow release and is made available to your plants gradually over several weeks or even months.
And there is less chance of the build-up of salts in the soil, as is common with synthetic fertilizers.
Many organic fertilizers such as compost also help to build your soil, which is healthier for your plants long-term.
The benefits of liquid and granular fertilizers
Liquid and granular fertilizers each have their place in the garden and offer different benefits.
Consult this graphic when deciding which one to use and for what purposes:
What liquid fertilizers can you use
There are many types of liquid organic fertilizers. Local availability may be dependent on your location although you can also buy these online.
Usually liquid fertilizers are an emulsion where some solid organic material has either been blended with water to form a thick liquid or been steeped in water before being strained. The latter is usually called a “tea” not to be confused with tea you can drink!
Common ingredients include fish scraps, seaweed, worm castings, compost and manure.
Some of these, such as fish, have a strong odour, while others such as compost teas have a slight odour.
It is important that you look for the OMRI seal to ensure the materials used come from organic sources. For fish fertilizer you want to avoid any that contains fish from fish farms that were fed antibiotics or other medications.
When to use liquid fertilizer
A liquid fertilizer has the benefit of already being in a form that plants roots and foliage can take up and use.
Just like a smoothie that you make and drink, the nutrients in a liquid fertilizer are available to plants almost immediately.
That’s why I use a liquid fertilizer for young plants to give them a nutrient boost when they most need it.
This is especially key when you transplant seedlings into the garden. Transplant shock can be minimized by feeding your transplants with a liquid fertilizer in the first few days of being in their new environment.
It can also be used to give plants a boost if you see them struggling to grow.
What granular fertilizers can you use
Probably one of the most common granular fertilizers is compost. And you can make it yourself!
Often compost is mixed in with soil but it can also be used as a surface mulch which will slowly get mixed into the soil underneath by soil organisms such as worms. Nutrients in the compost will also leach down into the subsoil when watering or when it rains.
Manures can also be used similar to compost. While animal manures are popular some vegans don’t like using any animal products in their garden.
So mushroom compost/manure has become popular too, although that can contain animal products as well, depending on what was used to grow mushrooms in.
Another common type of granular fertilizer is a mix of various types of organic materials. It can include alfalfa meal, manure, guano (yes, bat poop!), dried blood, bone meal, crushed shells, fish meal, rock phosphate and other types of minerals.
While you can buy small quantities of any of these, bagged, ready to use, if you have a larger vegetable garden, you may want to buy in larger bags at a feed store.
When to use granular fertilizer
A granular fertilizer for plants is a slow release fertilizer, meaning that it takes a while for the components to break down so your plants can use them.
It’s like the full course meal you eat and it keeps you full for a long time.
I use a granular fertilizer when planting transplants to give the plant nutrients through most of its growing period.
It releases nutrients over the course of several weeks or even months, feeding plants gradually.
And as mentioned above the good thing with these organic fertilizers is that it is hard to burn your plants as the fertilizer is a slow-release type.
What is foliar feeding?
Another way to use a liquid fertilizer is to spray plant foliage (leaves and stems).
This is called foliar feeding and works as plants can absorb nutrients through their leaves.
Often used on greens like lettuce and mustards, it’s an even quicker way for plants to get their nutrients.
It is applied using a liquid fertilizer sprayer or can also simply be watered on with a watering can with a fine rose or spray attachment.
Can I use both liquid and granular fertilizer at the same time
I often will mix in my granular fertilizer into the planting hole and then plant my transplant.
That’s followed with a good drenching of the soil and the transplant’s leaves with a liquid fertilizer, usually fish and seaweed mixed.
This technique gives the plant the benefit of the immediate uptake of nutrients from the liquid fertilizer but then also the benefit of the slow release nature of the granular fertilizer.
Can I use these fertilizers indoors?
Growing vegetables indoors works well, if you can give them enough light and also fertilizer since usually you’ll use sterile potting or container soil.
You can use most organic fertilizers indoors. However keep in mind that some can have strong smells such as fish emulsion.
Stick to the less odorous fertilizers such as seaweed, worm casting and compost teas if using liquid fertilizers.
Most granular fertilizers are okay as you lightly rake them into the soil. However be careful as some could introduce mold in the closed confines of indoors.
These fertilizers are great to get plants growing well. However over the long haul, doing what you can to build your soil and have healthy soil is your ultimate goal.
In fact many no-dig vegetable gardeners don’t use any fertilizers. All they do is once a year, add a thick layer of compost to all of their beds. This helps to build the soil and acts as a living mulch for plants.
Watch my video for more info on what I’ve experienced with no-dig:
And check out Charles Dowding for more information. His YouTube channel is full of videos showing the results he gets from this simple technique.
So armed with this info, you can now feed your plants the right fertilizer at the right time, knowing you’re only putting on organic materials.
If you enjoyed this article, have something to add or have any questions, please leave a comment below.
Wishing you all the best!
Tranquil Urban Homestead, Victoria, BC