Fertilizer for Improved Plant Root Growth

Written by amanda gaddis
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Fertilizer for Improved Plant Root Growth
Some fertilisers encourage root growth. (Martin Poole/Photodisc/Getty Images)

When starting seeds or establishing plants in the garden, gardeners need to use fertilisers that will improve root growth. These types of fertilisers may be known as starter, pop-up, planting or root fertilisers, and they are usually high in phosphorus (P) and potassium (K) to encourage root growth in seedlings. Improved root growth in young plants lets plants take in more nutrients to grow faster and produce more fruits, vegetables or flowers once mature.

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A well-developed root system will lead to a thicker, fuller lawn, so root fertilisers can be very important for grass. The root systems of turf grasses generally grow more vigorously during cooler weather in spring and fall, so gardeners should apply granulated root growth fertilisers in these months. Lawn care experts recommend fertilising in April with a solid root growth fertiliser that also contains a weed control product to prepare lawns for summer, then fertilise again in late October with a 13-25-12 fertiliser, which is high in phosphorus, to encourage root growth over the winter.


Annual and perennial flowers can be heavy feeders, needing regular fertilisation to maintain high yields of flowers. Fertilisers that are high in phosphorus and potassium will encourage root growth in flowering shrubs and plants. Gardeners can mix solid fertilisers in with soil before planting or transplanting, but liquid fertilisers can be easier to apply and are often more easily absorbed by root systems. Many gardeners recommend applying liquid fertiliser when starting seeds, and it can be especially important when transplanting flowers into a garden bed or container.


Like grass and flowers, trees need fertilisers high in phosphorus and potassium to stimulate root growth. Gardeners should apply fertilisers as close to the roots of trees as possible, so granulated fertilisers spread on top of the soil are less effective than liquid fertilisers. Granulated root growth fertilisers can be applied directly into soil when trees are being transplanted. Like grass, trees do most of their root growth in fall and winter when soil temperatures are between -1.11 and 18.3 degrees Celsius, so gardeners should apply high P-K liquid fertiliser in the fall to stimulate growth over the winter months.

Rooting Hormone Fertilizers

Some fertilisers contain what are called "rooting hormones" that are said to stimulate root growth in seedlings and cuttings. The most common root hormone is indole butyric acid, and it is often used in conjunction with B vitamins like thiamine. Most rooting hormones sold in gardening stores have been developed by fertiliser companies and contain proprietary mixes of ingredients. In powdered, gel or liquid form, rooting hormones are available alone or as part of starter fertiliser products.

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