Watering Vegetables - Philip Drew ( 2009)
(The information in the text and table below has been taken from 'Know and Grow Vegetables' - PJ Salter, JKA Bleasdale and others. Excellent and relevant from thorough scientific research, though not organic. I'm told this book in now out of print though you may be able to buy it second hand. And perhaps if there has been enough demand, it has been reprinted. M.McC)
Water is one of the essentials to make plants grow and most gardeners assume that keeping vegetables well watered will pay dividends. In fact, this is not always the case and excess water can result in rotting, leaching of nutrients, dilution of taste, poor late growth and poor keeping qualities (in onions).All vegetables need water to start with, either from seed or when planted out. After this establishment phase is over, they usually grow very strongly and push roots wide and deep, 2 feet or more is common. This is usually early season when water is freely available in the soil and extra watering is totally unnecessary and can result in a weak root growth (with a poor subsequent performance) or the production of large amounts of something you don’t want – foliage on peas, for example. When the plant has grown, the onset of flower and seed formation, which is often the product you do want, means that the plant’s emphasis changes to the production of these and root formation stops. It is at this time that many plants need extra water and they respond very well if you apply it. Each vegetable does vary and the above is not a universal rule.
Watering technique is also important. Roots are usually deep and you need impractically large quantities of water to get enough down there. The only way to help the plant is to target the roots – light sprays over the foliage or wetting ground are useless. This targeting is assisted if you build in depressions in the soil around the plant (peas/beans) or bury a bottomless bottle next to the plant roots (tomatoes). Often, though, you are just wasting time and water as the guide below shows. To give an idea of the magnitude of the task of manual watering, putting the equivalent on 1” of rain on a full size plot would require 6,350 litres, comfortably more than 6 tons!
One way of avoiding the time, expense and work of watering is to reduce evaporation by using a mulch around the plants. This should be applied after watering and, if more water is needed, pulled aside temporarily whilst the extra is applied. However, watering on allotments - where it usually has to be carried for some distance from the supply is hard work and it is important to reduce this chore to the minimum when you have many crops to cover.
Crops are divided into 3 categories:
Category A: Responds well to frequent watering
Category B: Water only at sensitive stages shown
Category C: Not very responsive, water only as advice.
Cabbages - all types, as frequently as possible in dry weather
Calabrese - as for cabbages
Cauliflowers - at all times throughout growth but especially when hearting up
Celery - frequently
Chillies and Peppers - frequently especially during the fruit development and ripening stages
Coriander - as frequently as possible to prolong the leaf stage
Curcurbits - Courgettes and Marrows, squash and pumpkin, cucumbers - as frequently as possible throughout growth
Lettuces - as frequently as possible
Potatoes, early - for good yields water frequently, especially at the marble stage
Spinach - as frequently as possible.
Tomatoes - frequently for indoor tomatoes at all stages
Beans - all types, at the start of the flowering stage and throughout the pod-forming and picking stages
Peas - At the start of flowering and throughout the posforming and picking stages
Early Potatoes - water at the 'marble' stage
Maincrop potatoes - as often as is practical once the 'marble' stage has been reached
Sweet-corn - at the tasseling and cob-swelling stages
Tomatoes - outdoors - to get plants established and at flowering and fruiting stages
Beetroot - in very dry conditions, before soil becomes too dry and growth is checked
Winter Broccoli - to get plants established after transplanting and in late summer if the weather is dry
Brussels Sprouts - for a few weeks after transplanting to ensure plants have established
Carrots - to ensure seed germinate and before soil become too dry for plants to develop
Leeks - water well on transplanting to ensure the plants have established. More only in very dry weather
Onion bulbs - water to get plants established
Salad onions - water seeds to ensure good germination
Parsnips - water to ensure germination and if soil becomes too dry
Radishes - water to ensure germination then only as necessary
Shallots - water as necessary to get established