A sudden yellowing of the oldest leaves occurs uniformly from top to bottom. The leaves at the branch tips remain green and healthy. Once the yellowed leaves drop off, no further yellowing and leaf drop occur. Water from the soil enters the plant through the tiny root hairs at the end of the roots. Some drought-resistant plants have extensive root systems with a large active surface area which is capable of rapid growth into the deeper subsoil strata where moisture may be available.
Native grasses are also very deep rooted.
Alternatively, some of these plants have shallow, fibrous roots systems which simply act as a sponge, immediate absorbing any rainfall which might fall on the soil surface. Coarse sand or perlite are excellent soil additions to improve drainage, and organic matter is also beneficial. When preparing a soil for planting or repotting, it is recommended to use about two parts coarse sand or perlite with one part organic matter and one part good garden soil. If the garden soil is fairly sandy, use equal parts of these ingredients. This is the time of year to start your onions so they can produce bulbs that are large enough for harvesting before fall frosts.