Sponsored by Osmocote

How do you keep your plants supplied with nutrients throughout their life? Easy! Slow-release fertilizers are designed to feed houseplants, garden veggies, and lawns over time to provide them with nutrients throughout the growing season. New fertilizer prills are encased in a protective coating that controls the release of nutrients into the soil and feeds plants at regular intervals rather than all at once.

NPK Ratio

three essential plant nutrients

Before committing to a particular plant food type, be sure to check the NPK (nitrogen, phosphorus, and potassium) ratio printed on its label. These three numbers represent the percentage of each essential nutrient in the fertilizer. Nitrogen promotes plant growth and healthy leaf coloring, while phosphorus assists in the development of new roots and the production of seeds, flowers, and fruit. Potassium keeps plant stems nice and strong. You'll ultimately want to buy a fertilizer with the best NPK ratio for your greenery. Running a soil test is an easy way to determine what nutrients your garden is lacking.


To apply slow-release fertilizer, simply mix the prescribed amount a couple of inches down into the soil. Since the fertilizer's nutrients are literally "released slowly," you won't have to feed your plants again for several months. In warmer seasons, however, the prills' nutrients are released at a higher rate to keep everything healthy and growing. During these hot spells, you may find yourself having to apply fertilizer just a little more frequently. Note, however, that herbs grow better with less fertilizer and should only be fed half the recommended amount.

As long as the ground in your yard isn't frozen, you'll want to start mixing fertilizer into your soil during the spring. Plants awakening from their winter dormancy are eager to begin growing, and a hearty dose of nutrients is just what the garden doctor ordered. Melting snow, spring rains, or (in the case of houseplants) regular watering should create enough moisture for the nutrients to be released.

When transferring annuals from flats or pots to your garden, put a small amount of plant food in the bottom of each planting hole to help them get established. Follow up with a second feeding in four to six months for optimal flower production. Perennials, on the other hand, should be fed in the fall to promote strong root growth before the onset of winter.


Different types of slow-release fertilizer will benefit different parts of your garden. For instance, Osmocote's Flower & Vegetable formula boasts a balanced NPK ratio of 14-14-14 and can be used to feed trees, shrubs, perennials, and heavy fruit producers like tomatoes, melons, and berries. This fertilizer contains twice the amount of slow-release nitrogen than other forumlas and is sure to net you a bountiful harvest. If you need a product for indoor plants, annuals, container gardens, or raised beds, you're going to want a fertilizer that has more nitrogen and less phosphorus, like Osmocote's Outdoor and Indoor Formula.

If your needs are more general than this, you might consider buying a multipurpose formula, which not only has an NPK ratio of 15-9-12, but also includes nine other beneficial nutrients. This formula works well with a variety of plants, from ground covers and trees to flowers and acid-loving plants. The fertilizer is so densely packed with nutrients that it only needs to be applied once every six months.

safely handling plant food

You might be wondering how a one-time application can sustain your plants for so long. The answer is in the coating, which is made from a semi-permeable oil resin that naturally decomposes over time. So, while all the fertilizer's nutrients are inside of the prills, only a fraction of them will become exposed to the soil at a single time. For this reason, slow-release plant foods can be applied at almost any time of year. The prills' coating also makes this fertilizer safe to handle, though you should always wear gloves and wash your hands when exposing yourself to garden products as a matter of caution. Store plant food in a cool, dry place that is inaccessible to children.

Master gardener, author, and columnist Marianne Binetti provides information and answers questions on Osmocote product usage at plantersplace.com. This site is full of gardening recommendations and is a great place to learn more about slow-release fertilizers and their many benefits. Your garden will thank you later!