When it comes to giving your plants and flowers a summer boost, you’re spoilt for choice. Among the vast array of houseplant and garden fertilizers, you’ll also come across some named ‘plant food’ too – but what’s the difference?
Fertilizer enriches the soil with vital macro and micronutrients to aid plant development, whilst commercial plant food has a much lower concentration of nutrients. In its true sense plant food is created during photosynthesis when soil nutrients are combined with atmospherical elements.
Garden center products vaguely labeled ‘plant food’ contain little to no nutrients and won’t provide your plants with the tangible, long-term benefits of fertilizer.
To help clear up the confusion, we’ll explore the differences between genuine plant food and fertilizer, plus our guide for when to apply fertilizer, a look at the contents of common fertilizer, and more.
Plant Food vs. Fertilizer
The main difference between the two is that one is a natural process whilst the other is a prepared mix of plant ‘boosting’ natural and chemical nutrients. Let’s look at what each is and how they work…
What Is Plant Food?
Plant food is essentially the photosynthesis process, whereby plants create sustenance for themselves using a combination of nutrients absorbed from the soil and the help of sunlight, water, and air to convert this into usable energy.
How Do Plants Make Their Own Food?
As carbon dioxide enters a plant’s leaves from the air, it combines with chlorophyll and uses the sun’s energy to form ‘chloroplasts’. These chloroplasts create glucose molecules that connect and travel throughout the plant with the help of water to make starch and cellulose.
These glucose by-products respectively store energy and help build cell walls. All the while, water transports soil nutrients up through the roots, combined with the newly-created sugars to nourish the plant.
Fertilizer is a soil additive that promotes foliage or flower growth and can either be synthetic or organic. Most commercial fertilizer products come in liquid or water-soluble ‘granule’ applications and contain chemical forms of essential nutrients – chiefly Nitrogen, Phosphorus, and Potassium.
These appear on products as a set of 3 NPK numbers aka 10-10-10 or 20-5-5 relating to the ratio of each nutrient, which varies depending on the plant’s needs.
Natural or organic fertilizers, meanwhile, contain plant and animal-derived ingredients such as manure and bone meal which are taken up gradually by the plant’s roots and are less likely to damage plants if used in excess as they don’t contain chemical salts.
These are the 3 main nutrients required for plant growth:
- Nitrogen (N)
- Phosphorus (P)
- Potassium (K)
These 7 nutrients are used in trace amounts:
- Boron (B)
- Zinc (Zn)
- Manganese (Mn)
- Iron (Fe)
- Copper (Cu)
- Chlorine (CI)
- Molybdenum (Mo)
This can make up 50% of commercial fertilizer content and provides no direct value to plants but is there to help disperse the nutrients and increase absorption. Filler material is often derived from things like clay, limestone, and sand.
What Does Fertilizer Do?
The macronutrients respectively encourage leaf and root growth, fruit/flower development, and improve overall plant functions. Whilst the smaller but no less vital micronutrients help bolster plant health by correcting nutrient deficiencies, balancing soil pH, and promoting disease resistance.
Essentially, fertilizer in either synthetic or organic form enriches poor soil that is lacking in the essential nutrients so that plants can grow bigger, and therefore produce more food for themselves!
In chemical fertilizer, different nutrient ratios are manufactured if gardeners wish to specifically target foliage growth e.g. for leafier vegetable greens, flower abundance with ‘bloom boosters’, or improve overall growth with ‘all-purpose’ fertilizers.
In the case of natural fertilizer, plants are given a balanced source of nutrients, feeding the microbes living in the soil like fungi and other bacteria, which in turn helps break down these nutrients to improve plant development.
Why Are Some Fertilizers Labeled as Plant Food?
The terms are used interchangeably because they’re thought to provide plants with similar benefits. According to the Royal Horticultural Society fertilizer products labeled ‘plant food’ are usually soil additives with no specified nutrient content and may describe their product in these terms if the “materials are not covered by fertilizer regulations.”
Best Time To Fertilize Plants
When applying fertilizer, bear high temperatures and heavy rainfalls in mind. Heat-sensitive plants, for example, will require less fertilizer during heatwaves.
Fertilizer is also best when watered in, so doing so after heavy rain causes the product to ‘sit’ on the soil surface or risk damage by sticking to foliage.
Time of Year
Plants are best fertilized monthly within their active growing season throughout spring and summer.
In warm climates, fertilizer can be applied in early spring but as many regions are still at risk of frost at this time it’s normally wise to wait until early summer.
Time of Day
Morning is ideal before plants become stressed by the midday sun and you can apply the product in low winds. Try to time their watering schedule straight after fertilizing for maximum uptake.
Phases of Growth
Plants in their young seedling stage can benefit from balanced all-purpose fertilizer to encourage green, leafy development and once the mature foliage is well underway, high-phosphorus or bloom booster fertilizers can be applied to promote fruiting and flowering.
Best Time To Fertilize Lawn
Timing your lawn fertilizer application appropriately allows the grass’ roots to sufficiently absorb the nutrients. Doing so in overly rainy or hot weather can mean it going to waste or risking fertilizer burn.
Time of Year
Editor of Homes & Gardens Lucy Searle recommends fertilizing your lawn 3 times in spring, summer, and fall “this is to help with healthy growth after the last frost passes; to help it beat the heat and restore color, and finally to help it withstand the onslaught of winter.”
Time of Day
According to Scotts Lawn Care, late afternoon or early evening is best to prevent the sun’s rays burning your grass, “as ‘lush green’ won’t be achievable with burnt grass blades.”
Phases of Growth
As with plants, lawns will respond best to fertilizer when the grass is starting to actively grow and turn green. If you have grown your lawn from grass seed, you can apply an organic lawn fertilizer to aid growth shortly after germination.
How Often To Fertilize Indoor Plants
Houseplants can be fertilized once a month during their active growing season (normally between March and September). Don’t fertilize during the colder months as plants enter dormancy in winter and won’t be able to absorb the nutrients, leading to soil and foliage damage.
Iowa State University urges indoor gardeners to follow the application instructions on unique fertilizer products as advice can range from every 2 weeks to every 3-4 months.
How To Prevent Fertilizer Burn
1. Only use the recommended amount stated on the package
2. Make sure you apply fertilizer at soil level only as foliage will burn when salts settle on it. Wash any residual product off leaves with a hose.
3. In the case of lawn fertilizing, use a spreader to distribute the product evenly to prevent concentration in one area. You can use push-along spreaders for long, large lawns or handheld spreaders for small/irregular-shaped areas.
4. Top dress your lawn with compost or go for organic over synthetic lawn care when you can.
5. Opt for slow-release fertilizer as these provide a steady release of nutrients overtime, reducing your application frequency.
How Do You Fertilize Houseplants Naturally?
Organic household waste is a popular choice for natural houseplant fertilizer as these materials are packed with beneficial nutrients and have gone through minimal processing. Items like pulverized eggshells, banana peel, and coffee grounds can be turned into compost at home.
What Does Fertilizer Burn Look Like?
Excess fertilizer salts dehydrate plants and foliage, resulting in yellowing leaves, brown leaf tips, dropping foliage, stunted growth, and a white chalky build-up of mineral salts on the soil surface. You should also check plant roots for limpness and discoloration (from tan to brown/black).
To sum up, plant food is, as the term suggests nature’s fertilizer and refers only to the food plants create themselves via photosynthesis whilst fertilizer is a soil additive containing the most vital plant-growing nutrients.
Plants grown in healthy, fertile soil – whether garden plants or houseplants – won’t always require fertilizer.
But if you do need to give your veg or flower patch a boost, just be sure to read the label carefully to prevent damage and try checking out organic alternatives where possible to give your greenery a gentler balance of nutes!