Plant Food & Fertilizer Explained

By Andy McIndoe

What Should I Feed My Plants?

This must be one of the most frequently asked questions. Some of us tend to think of some of our plants like our pets: they are fed regularly, in the belief that they will use all those nutrients we supply them with.

In other cases some of our plants are totally neglected; we completely forget that they haven’t had any sustenance for ages. Feeding them seems wasteful and unnecessary. Plants growing in the natural environment are adapted to the soil conditions.

A garden situation is different. Cultivation is more intensive and we introduce different plants with different nutritional requirements. Therefore, to get the best results we need to consider feeding more carefully.

I dealt with the basics of plant feeding in a previous post: (click here) so I thought this time I would give my top recommendations for the best fertilisers to use for certain plants and situations.

2 Young plants may need some feeding

Seedlings and young plants

If young plants are raised from seed in a seed and cutting potting medium there is very little nutrient available. The reason is that higher levels of feed in the soil can cause damage to young roots and inhibit germination.

If you are going to plant them out straight way no feeding is required. However if they are to remain in the seed mix for a few weeks then it is best to apply a dilute general liquid fertiliser to keep them growing and avoid starvation.

Mix the fertiliser at half the strength recommended for mature plants and apply weekly until they are planted out.

3 Adding controlled release fertiliser

Plants in pots

Most potting mixes contain sufficient nutrients for 4 – 6 weeks; after that supplementary feeding is necessary. Incorporating a controlled release fertiliser at the time of potting, or adding it to the surface of the growing medium of established plants is the simple way to add a season’s supply of feed.

Controlled release fertilisers are little round pellets that release nutrients when it is warm enough and the soil is moist enough.

Alternatively you can use a liquid or soluble general-purpose fertiliser which is diluted in water and watered on to the plants at regular intervals. This delivers the feed to the plants in readily available form, but it is more laborious.

Personally I would do this two or three times during the growing season to give plants, especially seasonal bedding plants, a boost and I would do this in addition to adding the controlled release fertiliser.

I would use tomato fertiliser for this as it contains plenty of nitrogen for growth, in addition to loads of potash for flowers.

4 Roses, shrubs and perennials need slow release feed

Plants in the ground

An application of a general slow release NPK, fertiliser around established shrubs and perennials in spring should supply all the plants need for the coming season.

This is in addition to garden compost or well-rotted manure which are really soil conditioners that also supply some nitrogen. It is always best to use a specific rose fertiliser around your roses: these are greedy feeders that need loads of nitrogen, potash and various other trace elements which can be lacking in many soils.

You could also use that rose fertiliser around your flowering and foliage shrubs. If you want an organic alternative choose fish, blood and bone. Bone meal only supplies phosphate and some nitrogen; that’s why it is used to encourage root development when planting.

Don’t forget that mature shrubs and hedges are in the same position for a long time. They often miss out on fertiliser application. Feeding with a slow release fertiliser of an organic concentrate will give them a real health boost and you will have better looking plants.

5 Using a hose-end dilutor

For a general tonic and to give the whole garden a boost in the growing season you can apply a liquid or soluble fertiliser through a hose end dilutor.

This delivers nutrients through the leaves as well as through the roots. This is not the most economical way of feeding, but at least you are watering at the same time.

6 Applying liquid tomato fertiliser

Tomatoes and fruiting crops

These require a fertiliser that is high in potash, the nutrient used by the plant to produce flowers and fruit. They also require plenty of nitrogen to stimulate growth.

For tomatoes, aubergines, bell peppers and chillies I would always recommend a liquid tomato fertiliser.

This is normally applied after the first flowers have set, in other words been pollinated. However if plants are growing slowly and are clearly lacking food a weak application of liquid fertiliser prior to that will keep things growing.

7 Fruiting hedge needs potash

Fruit bushes and fruit trees can be fed with a general slow release fertiliser that is high in potash.

If soil is very well drained and generally poor a light application of sulphate of potash in spring and again in summer helps to harden growth and stimulate fruit bud production.

Potash is very soluble and is easily washed from the soil so this is particularly beneficial in wet seasons and where regular irrigation is necessary.

Sulphate of potash can also be applied to ornamental shrubs and climbers that are reluctant to flower. This is done in mid-summer as the following year’s growth is starting to develop.

8 Rhododendrons need an ericaceous fertiliser

Rhododendrons, camellias and ericaceous plants

These need a fertiliser that is specifically formulated for lime-hating plants. The granular types are the easiest to apply once a year, but don’t forget to water if weather is dry.

Sulphate of iron or sequestered iron is often applied in the belief that it is a good fertiliser for ericaceous subjects. It only supplies iron which can help to correct a deficiency. It does not supply the other basic plant nutrients.

Chicken manure pellets applied after flowering as new growth commences give established rhododendrons and camellias a boost.

9 Growmore fertiliser

Can I use “Growmore” as a general fertiliser?

This chemical fertiliser is well known in the UK, and versions exist elsewhere in the world. Growmore is a fast release NPK feed which is best used as a general fertiliser on the vegetable patch which it was originally developed for.

A slow release fertiliser is a better choice for most permanent garden plants. Organic fertilisers are generally slow release and even if the amount of nutrients they contain is less, they release them over a longer period.

If you have questions about specific plants or fertilisers do post them below:

Andy McIndoe

... Read more

Stay inspired

Get FREE Gardening tips and ideas from our experts in your inbox.

You can unsubscribe at any time


Related posts

Our best selling courses

Trusted by our partners