Some perennials, and herbs

Perennial plants were eaten more commonly in the past than nowadays because they can grow wild, and people foraged more than is common now – most people have little or no access to hedgerows, ponds and other wild areas. Why grow perennial as opposed to annual vegetables?

• They save the effort of resowing or replanting.
• They take less time to look after.
• They have fewer disease problems.
• They can be grown, say, as part of a ‘woodland garden’.
• Many crop early in the year, often before annual vegetables are ready to harvest.

Is it all positive?

• Most perennial plants grow better from replanting or dividing at some point, to maintain harvests.
• Perennial vegetables develop extensive root systems that require plenty of space.
• You need to weed and mulch, for best harvests and easy management.
• You need to spend time on maintenance, such as clearing old asparagus stems.
• In temperate climates there is an imbalance of harvest times, with most in spring, suggesting their role is complementary to, rather than instead of, annual vegetables.

In a no dig, weed-free garden, annual vegetables are not a great deal more work to grow than perennials.

The most time-consuming job in vegetable growing is harvesting, which applies to both annuals and perennials.

This first part of this lesson looks at vegetable perennials, those I consider most likely to give you decent harvests. (There is information on soft fruit in the two videos.)

Alliums

There are many perennial onions and leeks, all easy to grow and multiply. A spacing of 30 cm / 12 in is good, and planting in spring or autumn is easiest.

It’s about types and then subtypes. Colloquial names can mislead, especially ‘elephant garlic’, which is really a swollen leek stem, of mild flavour and stunning appearance.

Onions

Egyptian (‘walking’, ‘tree’) onion (Allium cepa proliferum) sows itself by onions on stem ends falling at random. Some stems have little onions within them.

Welsh onion (Allium cepa fistulosum) offers continual growth of new leaves with only small bulbs. I value it as a ‘perennial spring onion’, with healthy green growth most of the time.

Leeks

Leek (Allium ampeloprasum var. sectivum) makes a spreading clump of small leek stems. If you thin them they can grow bigger. Start by buying a plant, which may be called Babbington leek. Then, once or twice a year, divide off and replant a few side roots with a stem.

Asparagus (asparagus officinalis)

Like seakale, this is native to the seashore. Plants will always benefit from a mulch of seaweed, and be more nutritious for it.

Great positives of asparagus are the wonderful flavour and continuous harvests all through spring’s hungry gap. You can expect 25 or more spears per plant, say 1.3 kg / 3 lb.

I am writing about green asparagus, not the blanched white stems which are common in some countries. Green ones grow on level ground, are easy to manage and quick to harvest.

Plants of all male hybrids give a high yield, such as Gijnlim, Guelph Millennium and Mondeo.

Non-hybrid varieties have female plants that flower and set red berries by autumn. These are liked by flower arrangers, but they drop seed and become a nuisance weed. It’s worth cutting out stems with berries in September, to avoid growing a profusion of mini asparagus spears.

Propagating and transplanting

Either sow seeds under cover in spring, for eventual plants in 7–10 cm / 3–4 in pots; set them out in the ground early in the following spring.

Or buy crowns, the roots of one-year-old plants, to place 7–8 cm / 3 in below surface level, preferably in early spring. Space at 60 cm / 24 in, and if growing more than one row, space them at 1 m / 3.3 ft.

Picking

You may take a small harvest in year three, then more in year four. The roots (‘crowns’) need those early years to grow large, before you can keep picking for a whole two months.

The harvest period starts as soon as you see spears, and ends at summer solstice.

If you continue to harvest after the solstice, this results in weaker growth the following spring, because roots have had less time to recharge from photosynthesis by the new leaves.

Maintenance and pests

In late autumn, cut all of the fern stems to ground level (we use a scythe), then compost them after cutting. Or you can lay them on a path nearby, and then trample – they disappear into the soil by late summer, leaving just a pale straw of old stems.

You need to maintain soil in a weed-free state, so keep pulling the few annual weeds you see, when they are small. This is easy when you grow  asparagus on the flat, not on ridges. If there are perennial weeds amongst the crowns, remove them carefully and weekly until they disappear. We have used this method to eliminate bindweed (Convolvulus arvensis).

The asparagus beetle (Crioceris asparagi) can be a problem, causing deformation of spears in spring; they also eat the fern-like leaves in summer. It’s best to squash them regularly when seen. Make soil healthy with a compost and seaweed mulch to improve plant strength. Organic gardens may also have tiny parasitic wasps (Tetrastichus asparagi) which parasitise the Crioceris eggs. This is probably why at Homeacres we notice very few asparagus beetles during the summer, once the wasps have arrived. I’ve actually never seen the wasps!

Rabbits and slugs sometimes eat young spears.

Perennial kale (brassica oleracea var. acephala)

These plants give large harvests, and you may need only one. Leaves are a little less tender than those of the common biennial kales. You can look forward to picking leaves during many months each year, and for several years.

Varieties

• Taunton Deane, 2 m / 6.6 ft, whose height means it’s inclined to suffer wind damage and is difficult to net against birds. It can also take space by leaning over as it grows older.
• Daubentons, 1 m / 3.3 ft, has leaves that are more tender than those of Taunton, but its stems may snap off or recline on the surface.
• Asparagus kale, 75 cm / 2.5 ft, can grow from seed or stem and is low and sprawling. It offers leaves through the growing season then, in spring, tasty shoots like mini broccoli, after which it’s good to prune it back.

Propagating and transplanting

To make more plants, you use the plant’s habit of making new stems and sideshoots. Push down on the small stem of any shoot that is about 12 cm / 5 in long, to detach it from the larger stem.

Place the stem in a small pot of compost or in a garden bed, with one half of it below compost or soil level, and just the few leaves poking upwards. They then wilt, while the stem makes new roots within three to five weeks, depending on the season.

Or put stems in a glass of water on the windowsill, then transfer to pots of compost once you see the first shiny roots, after about two weeks.

Within about eight weeks, transplant your rooted cuttings outside, at any time from spring to early autumn – space them at 60 cm / 24 in.

Picking

First harvests are two to three months after planting. The stalks are fibrous; the leafy part is best for eating.

The harvest period is from early spring and through the hungry gap to late autumn, then some leaves in mild winters. Plants live for five years or longer, during which time they multiply stems and can grow to a substantial size. It’s worth cutting back the stems to a manageable height.

Occasionally plants die for no obvious reason, so it’s good to always have a spare or two.

Maintenance and pests

Occasionally remove sideshoots and yellowing leaves, for easier picking of larger leaves on remaining stems. Maintain a surface mulch, and stake plants if you do not have space for them to recline.

Pests are mainly summer caterpillars, but plants should survive their ravages.

These kale also suffer brassica pests such as pigeons and rabbits. Take your usual precautions, although plants are strong enough to regrow in autumn after being deleafed by caterpillars in summer.

Rhubarb (Rheum rharbarbarum)

Best growth is in a temperate climate, where winters are not too frosty and summer is not too hot or dry. The plants like having moisture around their roots for most of the year.

Rhubarb stalks have a strong flavour, and taste better sweetened because of their high acidity. They come in different colours and some crop earlier, some later. Timperley Early gives harvests from early spring, and The Sutton offers an extra level of flavour.

Growth can be forced in the spring, under pots to keep any new growth in darkness. This makes the stalks paler and sweeter while also weakening the plant roots a little, from leaves being deprived of light. Remove the pots after about a month.

Propagating and transplanting

Plant pieces of root, or potted plants with a rootball, in autumn to early spring, at 90 cm / 35 in. You can cut the edge off any expanding crown of rhubarb roots, to have some for transplanting. You can also sow seeds in spring, for a plant to set out in summer.

Picking

First harvests are in the year after planting, and the harvest period is from early spring to early summer (depending on the variety). Then stop picking so that new growth can feed the roots. I recommend not forcing because it weakens plants, although blanched stems are sweeter.

Yields can be high in moist weather, for three or four months after the first shoots appear. However spring frosts slow early growth and may damage new stalks, though plants then regrow quickly.

Maintenance and pests

Usually there is only a small amount of weeding. Give a mulch in early winter after the leaves die down, preferably of decomposed material such as old animal manure or garden compost.

Rhubarb is one of the easiest plants to care for, with no pests. It grows, you pick some, then after mid-autumn it dies back. Watering is worthwhile in dry spring weather when you want tender stalks.

Seakale (Crambe maritima)

Harvests are of best quality and most welcome during spring, though low yields are an issue. On the other hand, you can forage it for free by the seashore.

It’s a myth that leaves need to be forced before you can eat them – they are delicious green.

Then, after some early leaf harvests, the flowering shoots are tasty too, arriving in late spring.

• With each passing year you should have a larger plant, and it may crop for decades.

Propagating and transplanting

You can grow plants from seed, but most seed that I have purchased has poor germination, probably from being old. A better method is to buy a piece of root in late winter to early spring. Also you can cut outer roots from your own plants, to transplant in early spring.

Space at 40 cm / 16 in, although I suggest you grow just one plant to start with, to learn how it likes your soil and climate.

Picking

New leaves appear during any small increase of temperature after winter. They have a dense texture and super flavour. Pick just a few, because the plants are not prolific.

By late spring you see flowering shoots appear – you can pick most of these. Allow a couple to flower and you’ll be amazed at the scent of honey.

Maintenance and pests

Remove yellowing leaves in late summer to autumn, and then you have a dormant plant through winter, protruding above ground. Cover with straw if temperatures are often below –8°C / 18°F, and mulch with a little compost, or best of all seaweed.

Leaves may need protection from pigeons, while rabbits eat young shoots.

Sorrel (Rumex)

Sorrel is easy to grow and tolerates shade. Its leaves are acid in taste, with hints of lemon flavour. Plants live a long time – at Homeacres I have a nine-year-old clump of Buckler-leaved sorrel that grows as healthily as ever.

Two garden types are Broad-leaved (Rumex acetosa) for large leaves, and Buckler-leaved (Rumex scutatus) for small, round leaves, which are wonderful in salads and omelettes.

There is also Profusion (Rumex acetosa TM683), a large-leaved cultivar that does not flower at all – it has a strong flavour.

Propagating and transplanting

Sow at any time to plant in any season, though best in spring. Plants grown from seed have more genetic variation than if you grow them from root division. The leaves vary in colour from light green to dark green, and in shape from pointed to quite round. Also some plants will flower earlier than others.

Plant root trimmings or divisions at any time, preferably in early spring or autumn, then water well if planting in dry conditions

Space at around 30 cm / 12 in. Each plant will easily fill that space with roots and leaves, for several years.

Picking

Harvests are possible from early spring to autumn, while spring is the most prolific harvest period – you could pick a few leaves every day.

In cooler autumn weather, leaves are thinner and may develop brown spots – this is normal for the season and not a disease.

Maintenance and pests

Cut any flowering stems to the ground, whenever they appear. In late autumn you can spread 2.5 cm / 1 in of compost around plants of Broad-leaved sorrel. Or you can cut all growth to just above the ground in late spring when it’s flowering, then spread the compost on top. It will easily grow through, and with fewer flowering shoots.

Buckler-leaved sorrel flowers from June, and in July we either run a lawnmower over it at the highest setting, or cut it with a scythe. This results in new growth from August and until October. Then, in November, cut all old stems to ground level and spread 2.5 cm / 1 in of compost on top of the whole clump. New leaves then appear by early spring.

Apart from slugs, the most difficult pest is green dock beetle (Gastrophysa viridula), whose lava eats dock and sorrel leaves. If you notice many small round holes in the leaves, it’s probably them. You may also see their clusters of small yellow eggs on the underside of leaves. We control their numbers by regular removal of damaged leaves, so that most larvae and eggs go into the compost heap.

Herbs

Most perennial herbs are tough and pest free. As for all plants, a mulch of organic matter around their roots helps to keep them in robust health, and able to resist most problems. Annuals need more care, and bring their wonderful flavours at specific seasons.

Types

An easy herb garden would have mostly perennials, including some in pots. Add to their harvests by growing the biennials and annuals you like.

• Perennials include chives, garlic chives, fennel, mint, rosemary, sage, tarragon, thyme and lemon verbena; the latter is less hardy to frost than the others. The harvests are all fibrous or slightly woody, compared to the other two categories.
• Biennials are usually grown as annuals and include chervil, parsley, coriander and dill; they are all from the same umbellifer (carrot) family.
• Annuals are basil of all kinds, not hardy to frost and with tender leaves.

Seasonality

There are herbs that you can harvest at most times of the year. Grow a mix of perennials and annuals to increase your harvest choices and flavours.

In winter and early spring, perennials give decent harvests until they flower in late spring and early summer, after which you cut off the old flowering stems and some wood too.

Meanwhile, in spring, you have new shoots to pick on overwintered biennials such as parsley and coriander. Then, in early summer, spring sowings of annual and biennial herbs start to give leaves and stems, which continues through summer and autumn.

Perennial and annual / biennial examples

This is my selection for a range of flavours and harvest months:

• French tarragon (Artemisia dracunculus) is perennial, but does not survive winters in wet soil and is ideal for growing in containers. For example, I have one plant in a pot and move it into the greenhouse from February to April, to have some early harvests of new shoots. The flavour of mild anise and liquorice is far superior to Russian tarragon (Artemisia dracunculoides) which also grows more vigorously. The best harvests are in spring to midsummer – pick, and also thin new stems, at any time. During summer the stems grow small flowers and become tougher. After flowering, cut them back to a little above the original height.
• Lemon verbena (Aloysia citrodora), in a large pot, can live for several years. Move it under cover to avoid extreme cold through winter, though it does tolerate slight freezing in spring. New shoots appear prolifically all through the growing season and make a wonderful tea. In late winter, cut off new growth from the previous year and a few branches of older plants; for a while, it looks dead.
• Chives grow in three types: common chives (Allium schoenoprasum), Siberian chives (Allium nutans), and garlic chives (Allium tuberosum). They give repeat harvests almost all year and for many years. Keep removing flower stems, because unless you want new plants, their seeds can become a ‘weed problem’.
• Mints (Mentha, many types) are easy to grow in a pot or contained space to prevent them from spreading. Towards the end of summer, cut old and flowering stems back to 10 cm / 4 in – at this point they are often covered in mildew which is normal at that time, and not a problem.
• Parsley (Petroselinum crispum) is flat-leaved or curled, and seeds take two to three weeks to germinate. To pick parsley all year, sow in early spring and again in midsummer. It’s frost hardy to –7°C / 20°F and rich in vitamin C. Aphids often gather on new spring leaves of parsley, sometimes bringing a virus that turns leaves bright yellow. Jetting water onto leaves reduces damage, until predators arrive.
• Dill (Anethum graviolens) has two seasons of harvest: spring and autumn. For these harvest dates, sow in spring as early as you can (in February under cover, for example) then sow again in late summer from mid- to end of July. In summer, dill flowers and sets seed if you leave it, while in winter it’s damaged by frostslower than about –2°C / 28°F .

Fennel peculiarity

There are two completely different types of fennel:

• One is perennial and vigorous, a self-seeding herb (Foeniculum vulgare) which is either green or bronze. It’s best to cut it back before, or immediately after flowering, to prevent seeds falling; otherwise it can become a weed, and plants have strong taproots.
• The other is a bulb-type vegetable, Florence fennel, which is annual or biennial (Foeniculum vulgare var. dulce).

Propagating, planting and interplanting

PERENNIALS

These are easy to propagate, by cutting 7–10 cm / 3–4 in of new stem from mid-spring to early summer, to put in a small pot or module of moist compost. Push half of each stem into the compost, without any ‘rooting powder’, and within a month you should have rooted plants.

• The compost wants to be free draining, such as with three-quarters vermiculite or coir. I had a lesson in this from Jekka McVickar, whose herb nursery is worth a visit and whose books are well worth a read. Few people know or love herbs as much as Jekka.

Thyme and sage grow easily from seeds, mint and French tarragon from a fragment of root.

ANNUALS FROM SEED

Coriander (Coriandrum sativum) and dill (Anethum graveolens)

Make a first sowing from mid-February under cover, or plant outside with fleece over by the end of March. Spring plantings soon flower, so are not in the ground for long. They make an ideal interplant between onions and early potatoes.

Sow again in late summer, up to the middle of August. Coriander is especially strong in cool conditions. You can eat the green seeds too – in the US these are called coriander, while leaves and stems are called cilantro.

• The variety Cruiser, sown in late July to early August, often survives winter here without protection; temperatures sometimes fall to –7°C / 19°F, though not often.
• There are always a few plants that rise to flower in autumn. It’s best to twist them out, then the remaining plants grow larger.

Chervil (Anthriscus cerefolium)

This is sometimes called French parsley, except the leaves are way more tender and have a sweet taste of aniseed.

In the 1980s, it took me a few years to stop following the seed packets’ sowing dates. Most of what I grew from their recommendations to sow in spring were white flowers, because late spring is chervil’s flowering season.

Chervil’s best sowing time is late summer, with the reward of plentiful leaves throughout autumn and sometimes into spring. Chervil survives to –6°C / 21°F and lower, plus it tolerates wind from being so low to the ground.

INTERPLANTING EXAMPLES

A top time to transplant coriander, chervil and dill is late summer to early autumn. In our climate that is the first week of September for autumn harvests, and the last week for the highest chance of surviving winter.

However, most beds are full of vegetables in this season. Therefore you need to find spaces between plants that will finish growing within about a month, and that are not too dominant during that time.

Possible vegetables to plant herbs between include leaf lettuce and endive, cordon tomatoes, ridge cucumbers and some brassicas.

Longevity and pruning – perennials

Perennial herbs can live for ten or more years, therefore they’re worth pruning to maintain a compact shape, and not too large a size. Otherwise they grow long and bare wood stems.

It’s the same principle that one employs with lavender and flowering shrubs – cutting off most new growth immediately after the end of flowering. Usually it’s in mid- to late summer, and you just need to watch the plants to prune hard as soon as their flowers die.

This applies to:

• Sage (Salvia officinalis)
• Rosemary (Rosmarinus officinalis)
• Thyme (Thymus vulgaris, of the mint family)
• Mint (Mentha, many types)
• Oregano / marjoram (Origanum vulgare, of the mint family)
• French tarragon (Artemisia dracunculus)
• Lemon verbena (Aloysia citrodora)
• Fennel (Foeniculum vulgare)

Cut back harder than may feel right, at least 90% of new wood or stems and sometimes into old wood, especially if you can see small green shoots emerging from the wood. Plants look bare and denuded for a while, then suddenly grow new shoots on compact plants.

Herbs in containers

For perennials in pots, top up with a little fresh compost every year, or move them to a slightly larger pot. They stay smaller than the same plants growing in soil, and with little difference in flavour.

I especially recommend growing these three herbs in pots, for different reasons:

• French tarragon, so that its roots stay reasonably dry, in winter especially.
• Mint, so that it does not spread everywhere – it’s invasive. Even from a pot, suckers can nip out and root into soil or cracks in walls etc. You may not mind, but it’s good to know in advance.
• Lemon verbena, which, in climates with frosty winters, you can then move to a sheltered and less cold building during the coldest weather outside, when temperatures fall below –4°C / 25°F.

All herbs grow well in containers, of smaller volume than for vegetables because they grow more slowly, and tolerate dry roots to some extent.