We all know that an adequate supply of phosphorus is essential for healthy root growth but, during hot, dry months, we can further assist some of our vegetables to produce extra roots.
Pumpkins produce a huge amount of foliage – too much for the original root system to supply adequate water to the entire vine. Consequently, these plants and some other members of the squash family have evolved to produce roots at nodes (stem joints) along their runners. (See photo below.)
We can assist this auxiliary root formation by carefully lifting the runner and scratching the surface of the soil beneath where roots buds appear. Then cover this with a shovelful of compost and settle the runner back onto the compost. Encouraging extra roots to form will increase your crop.
These sections may be hidden by foliage but it will help to identify them if you place a soft drink bottle or large juice bottle (with the base removed) neck down beside this area. When watering, water not only around the base of the plant, but also into the bottles to supply water directly to the extra roots without wetting the foliage.
Tomatoes in their natural state, grow along the ground and will also form auxiliary roots along their stems, but our method of growing tomatoes tied to stakes prevents this. However, you can give them a helping hand to produce extra roots before planting out by lying potted seedlings on their side when they are 10-12 cm tall. Leave them like this for a week or so, depending on the growth rate, and remember to stand them upright for watering. As you can see in the photo, the main stem with make a 90-degree turn, and root buds will form on the horizontal part of the stem. Plant them out with the growth tip vertical and the horizontal stem just below the soil surface.
You can also hill up soil around tomato plants (a little at a time), and sweet corn plants to encourage extra roots to grow on the lower parts of the main stem.