How to Feed Established Plants – DIY Comfrey & Nettle Feeds
Feeding established plants
If borders and potting composts are well prepared, then additional feeding will be kept to a minimum. Ideally, annual plants in borders should not need any extra nutrients, but fruiting plants in pots and perennials will need feeding after a time.
There are no simple rules to tell you how much and when to feed, but, as a rough guide, annual fruiting plants such asand are most likely to need feeding from the time that they start to flower and form fruit up until their growth slows down at the end of the season. Perennial plants are most likely to need feeding when they are making most growth, ie. in spring (unless they have been repotted) and in summer. You can supply additional plant foods by the following methods.
- Adding organic fertilizers A mixture of equal parts of bone meal, seaweed meal, and hoof and horn gives a good balance of nutrients. A rate of 30g per plant per week will feed in 10-litre pots, whereas half the amount every couple of months is more suitable for a bay tree in a similar pot. Sprinkle the fertilizer mixture on to the surface of the compost or into holes made with a cane.
- Top-dressing with compost or well-rotted manure On borders, apply them at the same rate as you would for digging in. The richness and fine texture of worm compost makes it most suitable for top-dressing pots and other containers — use about a 1cm layer.
- Mulching with comfrey leaves A 5cm layer on borders will slowly rot down and release nutrients.
- Liquid feeding You can buy organic liquid feeds or make them yourself. They are useful for giving plants a boost, eg. when they are growing quickly, cropping heavily, or are recovering from pest attack. However, you should rely on them as little as possible. Proprietary organic liquid feeds are usually based on animal manures, and DIY ones on manure, comfrey, or nettles.
A traditional way of making a liquid feed is to soak manure in water. Quantities are rarely given and are difficult to specify since manures vary so much in composition. For well-rotted manure, try a 10-litre bucketful in 200 litres of water. The resulting liquid should be the colour of weak tea and can be used directly on cropping plants. Instructions for making comfrey and nettle liquids are detailed below.
Pure seaweed liquids contain only very small amounts of the major plant nutrients, which are not sufficient to feed plants in the same way as the other liquid feeds described here. However, they do contain essential trace elements and also natural growth promoters. Therefore, they can help plant growth, particularly root development, and in some cases can help increase the resistance of plants to pests, diseases, and frost. Use them at the recommended dilution either as adrench or a foliar spray.
DIY comfrey and nettle feeds
The leaves of the vigorous hybrid plant Russian comfrey, Symphytum x uplandicum, are rich in nutrients. They contain little fibre and, once cut, decompose rapidly into a thick dark liquid. This is relatively odourless compared to most DIY liquid feeds and stores well. It is an excellent source of potassium and contains smaller amounts of nitrogen and phosphorus. Dilute it ten to twenty times with water before use, depending upon the strength of feed required; eg. fruiting vegetables in pots benefit from about a 15:1 dilution (15ml water for every 1ml comfrey liquid) fed to them three times weekly when they start to form fruit. For pot plants use a 20:1 dilution once a week when they are growing strongly.
The liquid resulting from soaking nettles (Urtica dioica) in water is also a valuable plant food. It has a high nitrogen content and contains smaller amounts of potassium, phosphorus, and other minerals and trace elements, although its exact composition will vary with the year, the season, and the place where the nettles are growing. Young nettles picked in spring have the highest nutrient value. The liquid is best made in a sealed barrel (it is very smelly) and drawn off through a tap. Use approximately 1kg nettles per 100 litres of water. Use the liquid directly on fruiting plants such as tomatoes; dilute it with an equal amount of water for pot plants. Nettle liquid can also cause a rise in pH.
Decomposing comfrey leaves and comfrey liquid are alkaline and if used regularly at a high concentration they could cause a detrimentally high pH, especially on soils that are already alkaline. Do not use on acid-loving plants such as azaleas.